National Aeronautics and

Space Administration

IS20

George C. Marshall Space Flight Center

Marshall Space Flight Center, Alabama

35812
The NASA STI Program...in Profile

Since its founding, NASA has been dedicated to the 

advancement of aeronautics and space science. The 

NASA Scientific and Technical Information (STI) 

Program Office plays a key part in helping NASA 

maintain this important role.

The NASA STI Program Office is operated by 

Langley Research Center, the lead center for 

NASA’s scientific and technical information. The 

NASA STI Program Office provides access to 

the NASA STI Database, the largest collection of 

aeronautical and space science STI in the world. 

The Program Office is also NASA’s institutional 

mechanism for disseminating the results of its 

research and development activities. These results 

are published by NASA in the NASA STI Report 

Series, which includes the following report types:

• TECHNICAL PUBLICATION. Reports of 

completed research or a major significant 

phase of research that present the results of 

NASA programs and include extensive data 

or theoretical analysis. Includes compilations 

of significant scientific and technical data 

and information deemed to be of continuing 

reference value. NASA’s counterpart of peerreviewed formal professional papers but has less 

stringent limitations on manuscript length and 

extent of graphic presentations.

• TECHNICAL MEMORANDUM. Scientific 

and technical findings that are preliminary or of 

specialized interest, e.g., quick release reports, 

working papers, and bibliographies that contain 

minimal annotation. Does not contain extensive 

analysis.

• CONTRACTOR REPORT. Scientific and 

technical findings by NASA-sponsored 

contractors and grantees.

• CONFERENCE PUBLICATION. Collected 

papers from scientific and technical conferences, 

symposia, seminars, or other meetings sponsored 

or cosponsored by NASA.

• SPECIAL PUBLICATION. Scientific, technical, 

or historical information from NASA programs, 

projects, and mission, often concerned with 

subjects having substantial public interest.

• TECHNICAL TRANSLATION. 

English-language translations of foreign 

scientific and technical material pertinent to 

NASA’s mission.

Specialized services that complement the STI 

Program Office’s diverse offerings include creating 

custom thesauri, building customized databases, 

organizing and publishing research results...even 

providing videos.

For more information about the NASA STI Program 

Office, see the following:

• Access the NASA STI program home page at 

<http://www.sti.nasa.gov>

• E-mail your question via the Internet to 

<help@sti.nasa.gov>

• Fax your question to the NASA STI Help Desk 

at 443 –757–5803

• Phone the NASA STI Help Desk at 

443 –757–5802

• Write to:

NASA STI Help Desk

NASA Center for AeroSpace Information

7115 Standard Drive

Hanover, MD 21076–1320
i

NASA/TP—2010–216432

An Examination of the Hadley 

Sea-Surface Temperature Time Series 

for the Niño 3.4 Region

Robert M. Wilson

Marshall Space Flight Center, Marshall Space Flight Center, Alabama

May 2010

National Aeronautics and

Space Administration

Marshall Space Flight Center • MSFC, Alabama 35812
ii

Available from:

NASA Center for AeroSpace Information

7115 Standard Drive

Hanover, MD 21076 –1320

443–757–5802

This report is also available in electronic form at

<https://www2.sti.nasa.gov>
iii

TABLE OF CONTENTS

1. INTRODUCTION ............................................................................................................. 1

2. RESULTS AND DISCUSSION ......................................................................................... 3

2.1 Annual Averages of HadSST in the Niño 3.4 Region (1871–2008) ............................... 3

2.2 Monthly and 12-mma Values of HadSST in the Niño 3.4 Region (1871–2008) ............ 6

2.3 2-mma Values of Seasonally Adjusted Monthly Means of HadSST (D(m2))

 and SOI (SOI(2)) in the Niño 3.4 Region (1871–2008) ................................................. 27

2.4 The ONI Values in the Niño 3.4 Region (1950–2008) ................................................... 33

2.5. The Duration-Maximum Anomaly Association for ENSO Exteme Events .................. 34

2.6. Recurrence Periods of the ENSO Extremes .................................................................. 35

2.7 Decadal Aspects of ENSO Extremes ........................................................................... 38

3. SUMMARY ........................................................................................................................ 40

APPENDIX ............................................................................................................................. 43

REFERENCES ....................................................................................................................... 81
iv

LIST OF FIGURES

 1. Annual and 10-yma values of (a) mean and (b) high values of HadSST

in the Niño 3.4 region from 1871 to 2008 ................................................................. 4

 2. Annual and 10-yma values of (a) low values and (b) differences (high minus low) 

of HadSST in the Niño 3.4 region from 1871 to 2008 .............................................. 5

 3. Annual and 10-yma values of January values of HadSST in the Niño 3.4 region 

from 1871 to 2009 .................................................................................................... 11

 4. Annual and 10-yma values of February values of HadSST in the Niño 3.4 region 

from 1871 to 2009 .................................................................................................... 12

 5. Annual and 10-yma values of March values of HadSST in the Niño 3.4 region 

from 1871 to 2008 .................................................................................................... 13

 6. Annual and 10-yma values of April values of HadSST in the Niño 3.4 region 

from 1871 to 2008 .................................................................................................... 14

 7. Annual and 10-yma values of May values of HadSST in the Niño 3.4 region 

from 1871 to 2008 .................................................................................................... 15

 8. Annual and 10-yma values of June values of HadSST in the Niño 3.4 region 

from 1871 to 2008 .................................................................................................... 16

 9. Annual and 10-yma values of July values of HadSST in the Niño 3.4 region 

from 1871 to 2008 .................................................................................................... 17

10. Annual and 10-yma values of August values of HadSST in the Niño 3.4 region 

from 1871 to 2008 .................................................................................................... 18

11. Annual and 10-yma values of September values of HadSST in the Niño 3.4 region 

from 1871 to 2008 .................................................................................................... 19

12. Annual and 10-yma values of October values of HadSST in the Niño 3.4 region 

from 1871 to 2008 .................................................................................................... 20

13. Annual and 10-yma values of November values of HadSST in the Niño 3.4 region 

from 1871 to 2008 .................................................................................................... 21
v

LIST OF FIGURES (Continued)

14. Annual and 10-yma values of December values of HadSST in the Niño 3.4 region 

from 1871 to 2008 ..................................................................................................... 22

15. Monthly and 12-mma values of nonseasonally adjusted HadSST values 

from January 1871 to January 2010 .......................................................................... 27

16. Monthly and 2-mma values of the seasonally adjusted values of HadSST 

anomaly (D(m2)) from February 1871 to January 2010, where shaded portions 

reflect occurrences of warm EN events (positive anomalies) and cold LN 

events (negative anomalies), respectively ................................................................... 27

17. Presentation of 2-mma values of SOI (SOI(2)) anomaly from January 1871 

to January 2010 ........................................................................................................ 30

18. Results of epoch analysis for EN events, (a) D(m2) and (b) SOI(2) .......................... 31

19. Results of epoch analysis for LN events, (a) D(m2) and (b) SOI(2) .......................... 32

20. The ONI anomalies from January 1950 to January 2010, where shaded portions

reflect occurrences of warm EN events (positive anomalies) and cold LN

	 events (negative anomalies), respectively ................................................................... 33

21. Duration against (a) max ONI for LN and EN events (1950 – 2008) 

and (b) max D(m2) for LN and EN events (1871– 2008) .......................................... 36

22. RP-duration distributions for (a) EN events (1950–2008) based on D(m2), 

(b) LN events (1950–2008) based on D(m2), (c) EN events (2000–2009) based 

on ONI, and (d) LN events (2000–2009) based on ONI ............................................ 37

23. RP-duration distribution for (a) EN events (1871–2008) based on D(m2) 

and (b) LN events (1871–2008) based on D(m2) ....................................................... 37

24. Decadal variation of (a) NENO, (b) NENM, (c) NLNO, and (d) NLNM based 

on D(m2). The 2009 EN event observed in ONI has been included with 

the 2000–2009 decade, even though HadSST values have not yet been published ..... 39
vi

LIST OF TABLES

1. Annual and 10-yma values of SST in the Niño 3.4 region based on HadSST

monthly time series from 1871 to 2008 ....................................................................... 7

2. Frequency of occurrence of monthly high and low values of SST in the Niño 3.4 

region based on HadSST values from 1871 to 2008 ................................................... 10

3. HadSST monthly and 10-yma values for the Niño 3.4 region from 1871 

to April 2009 .............................................................................................................. 23

4. Listing of EN and LN events based on the HadSST dataset from 1871 to 2008 ........ 28

5. Frequency of occurrence of start, peak, and end times for HadSST-determined 

EN and LN events ..................................................................................................... 30

6. Listing of EN and LN events based on ONI (ERSST.v3b) ........................................ 34

7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST 

time series, ONI and SOI values, and the occurrences of EN (warm) and LN (cold) 

events from 1871 to the present .................................................................................. 44
vii

LIST OF ACRONYMS AND ABBREVIATIONS

2-mma 2-month moving average

12-mma 12-month moving average

10-yma 10-year moving average

D(m) difference between Hadley sea-surface temperature and the monthly-adjusted 

average (1871–2008)

D(m2) 2-mma of D(m)

DP double peak

e event end, based on Oceanic Niño Index

EN El Niño 

ENSO El Niño Southern Oscillation

ERSST.v3b Extended Reconstructed Sea-Surface Temperature, version 3b

HadSST Hadley sea-surface temperature

H(M) high (month)

L(M) low (month)

LN La Niña

M moderate

MP multiple peaks

NENM number of EN months

NENO number of EN onsets

NLNM number of La Niña months

NLNO number of La Niña onsets
viii

LIST OF ACRONYMS AND ABBREVIATIONS (Continued)

ONI Oceanic Niño Index

p peak

RP recurrence period 

S strong

s event start, based on the Oceanic Niño Index

SOI Southern Oscillation Index

SOI(2) 2-mma of Southern Oscillation Index

SP single peak

SST sea-surface temperature

VS very strong

W weak
ix

NOMENCLATURE

cl confidence level

CV coefficient of variation

na number above median

nb	 number below median

nra	 number of runs above median

PCS Pearson Coefficient of Skewness 

PI	 prediction interval

r	 coefficient of correlation

r2 coefficient of determination

sd	 standard deviation

se standard error of estimate

x	 independent variable in regression equation

y	 dependent variable in regression equation

z normal deviate for the sample
x
1

TECHNICAL PUBLICATION

AN EXAMINATION OF THE HADLEY SEA-SURFACE TEMPERATURE 

TIME SERIES FOR THE NIÑO 3.4 REGION

1. INTRODUCTION

The El Niño (EN) southern oscillation (ENSO) phenomenon has been described as the strongest oceanic-atmospheric tropical signal measured on interannual timescales.1–3 Although primarily 

perceived as a tropical Pacific event, as evinced by its strongly coupled sea-surface temperature (SST) 

and atmospheric pressure variations, the effects of ENSO impact Earth on a global scale.1,2,4–10

El Niño and La Niña (LN), respectively, refer to the anomalous episodic warm and cold water 

phases of the ENSO variation, when based upon SST, and to the anomalous negative and positive 

atmospheric pressure phases, respectively, when based on the Southern Oscillation Index (SOI).11,12

During an EN event, the westerly trade winds along the Earth’s equator weaken as atmospheric pressure rises in the western Pacific (Darwin, Australia) and falls in the eastern Pacific (Tahiti, French 

Polynesia). As a consequence of this action (called the Bjerknes feedback mechanism13), anomalous 

warming in the central and eastern Pacific occurs due to eastward migrating warm water from the 

western Pacific, which diminishes the strong cold-water upwelling off the South American coast.14,15

The reverse happens during an LN event (i.e., enhanced upwelling, positive SOI, and anomalous 

cooling in the eastern Pacific). When neither an EN nor a LN event is said to be occurring, conditions are more generally described as being ENSO neutral.

While the occurrences of EN events have been traced back hundreds of years, as gleaned 

from reports of anomalous rainfalls and storm events on coastal Peru, ship records, etc.,16–18 more 

recently, the use of SST, in particular those SST readings from the Niño 3.4 region (5° N.–5° S., 

120–170° W.) have provided the most reliable means for documenting the onsets, strengths, and durations of both EN and LN events. In fact, now, published monthly is the Oceanic Niño Index (ONI), 

a 2-month moving average (2-mma; also called the 3-month running mean) of the Extended Reconstructed SST, version 3b (ERSST.v3b) anomalies of the Niño 3.4 region, which provides an easily 

accessible means for monitoring the onsets, strengths, and durations of both EN and LN events, 

particular, from 1950 onwards.19,20

On the basis of the ONI, an EN event is said to be occurring when the index value measures 

0.5 °C or warmer for at least 5 continuous months. An EN event is termed “weak (W)” when the 

peak positive warm anomaly measures 0.5–0.9 °C, “moderate (M)” when the peak positive warm 

anomaly measures 1.0–1.4  °C, and “strong (S)” when the peak positive warm anomaly measures 

1.5 °C or warmer. Similarly, an LN event is said to be occurring when the ONI measures –0.5 °C 

or cooler for at least 5 continuous months. A LN event is termed W when the peak negative cool 
2

anomaly measures –0.5 to –0.9 °C, M when the peak negative cool anomaly measures –1.0 to –1.4 °C, 

and S when the peak negative cool anomaly measures –1.5 °C or cooler.

Previously, the decadal variation of EN events was examined using the ONI-determined listing of EN events (1950–2008) to investigate whether it could possibly be related to global warming or more simply be a manifestation of natural variation.21,22 From that study, it was found that 

the decadal variation of the number of EN onsets was better explained as one expressing normal 

fluctuation rather than one related to global warming. Surprisingly, it was also inferred that, for M 

and S events, a statistically significant linear relationship (at the 2% level of statistical significance) 

was found to exist between the onset of the next EN event (the recurrence period (RP)) and the last 

known duration of an EN event, strongly suggesting that another EN event likely would have its 

onset in 2009, which turned out to be true. Because EN, indeed, recured during 2009, a sharp reduction in the frequency of North Atlantic basin tropical cyclones during the 2009 hurricane season 

should have been expected and, indeed, was seen, with respect to earlier forecasts for the North 

Atlantic basin hurricane season.23–25

In this study, the HadSST dataset for the Niño 3.4 region is examined to determine the onsets, 

strengths, and durations of EN and LN events during the interval 1871–2008.26,27 Also, comparison 

is made against both SOI values for the same time interval and the ONI-determined listing of ENSO 

extremes since 1950 to see what differences might possibly exist,28 if any, especially with regard to 

the identification of the occurrence, strength, and duration of ENSO extremes. Additionally, the 

duration-maximum anomaly association for ENSO extremes and the RP-duration association, previously found for EN events using ONI, are investigated to determine if they also might exist using 

the HadSST dataset. Finally, decadal aspects of the ENSO extremes are examined, anticipating what 

possibly might lie ahead for the current decade (2010–2019).
3

2. RESULTS AND DISCUSSION

2.1 Annual Averages of HadSST in the Niño 3.4 Region (1871–2008)

Figure 1 displays (a) the annual mean and (b) annual high HadSST values in degrees Celsius 

for the interval 1871–2008 (shown as the thin jagged lines) and their 10-yr moving average (10-yma) 

values (shown as the thick smoothed lines). Figure 2 similarly shows (a) the annual low and (b) the 

annual difference (high minus low HadSST values) in degrees Celsius for the same time interval. For 

each temperature, the mean for the entire interval is plotted as the horizontal line: 26.95 °C for the 

annual means, 27.87 °C for the annual highs, 25.92 °C for the annual lows, and 1.97 °C for the annual 

differences. Also, for each panel, given are the standard deviation (sd), the coefficient of variation 

(CV=sd/mean), the median, the Pearson coefficient of skewness (PCS=3(mean–median)/sd), the 

number of annual values above the median (na), the number of annual values below the median (nb), 

the number of runs above the median (nra), the normal deviate for the sample results to determine 

whether the distributions are randomly distributed (z=(nra –na(nb+1)/(na+nb))/((na(nb+1)(na–1)/

(na+nb)2)(nb(na+nb – 1)))1/2), the highest and lowest annual value and their occurrence years, the 

50% prediction interval (50% PI), the inferred regression equation based on linear regression analysis against time (y), the coefficient of correlation (r), the coefficient of determination (r2, a measure 

of the amount of variance explained by the inferred regression), the standard error of estimate (se), 

and the confidence level (cl) of the inferred regression, except for the annual lows since the inferred 

regression and the mean were essentially the same.

For the annual means (fig. 1a), one finds its highest value to have occurred in 1877, measuring 

28.30 °C, and its lowest value to have occurred in 1890, measuring 25.78 °C. Runs testing indicates 

that the distribution of yearly means is nonrandomly distributed (z=–2.38). The inferred regression 

suggests a slight warming with time (about 0.00154 °C per yr), although the inferred regression is 

only of marginal statistical significance (cl>90%), suggesting that the inferred regression probably 

can be disregarded. In fact, the inferred long-term warming disappears if one neglects the earliest 

portion of the data (i.e., that part prior to about 1895). The nonrandom nature of the distribution of 

annual means may simply be a reflection of its decadal variation (represented by the thick smoothed 

line). The decadal variation is strikingly upward from about 1950 to 1995, increasing from 26.68 °C 

in 1951 to 27.28 °C in 1994, with large peaks in 1962 and 1982, a large dip in 1971, and a shallow 

dip in 1985. Since 1994, the trend in decadal values has been downward, falling below the long-term 

mean in 2003. About 25% of the time, the annual mean is found to exceed 27.34 °C, and about 25% 

of the time it falls below 26.56 °C.

For both the annual high (fig. 1b) and low values (fig. 2a), one finds similar episodic behavior 

(i.e., based on the 10-yma values) akin to that of the annual means, although the behavior demonstrated by the lows seems strikingly more pronounced. While the annual highs appear to be randomly 

distributed, the lows, in contrast, appear to be nonrandomly distributed (like the annual means). 

Neither the annual highs nor lows have statistically significant inferred upward linear regressions 

against time. For the highs, the highest high occurred in 1878, measuring 29.19 °C, and the lowest
4

 

1880 1900 1920 1940 1960 1980 2000

27.5

28.0

28.5

29.0

29.5

26.5

27.0

Year

1880 1900 1920 1940 1960 1980 2000

Year

26.5

27.0

27.5

28.0

28.5

26.0

25.5

Annual Mean HadSST Annual High HadSST 

 y = 23.97 + 0.00154x

 r = 0.108, r2 = 0.012

 se = 0.41, cl > 90%

 y = 25.03 + 0.00147x

 r = 0.099, r2 = 0.010

 se = 0.50, cl < 90%

mean = 26.95 

sd = 0.57

CV = 0.021

 median = 26.985

PCS = –0.18

na = 69

nb = 69 ⇒ z = –2.38 ⇒ nonrandom

nra = 28

 High = 28.30 (1877)

 Low = 25.78 (1890)

 50% PI = 26.95 ± 0.39 

 mean = 27.87

sd = 0.58

CV = 0.021

 median = 27.865

PCS = 0.03

na = 69

nb = 69 ⇒ z = –0.68 ⇒ random

nra = 33

 High = 29.19 (1878)

 Low = 26.55 (1893)

 50% PI = 27.87 ± 0.39

y

y

 

(a)

(b)

Figure 1. Annual and 10-yma values of (a) mean and (b) high values

of HadSST in the Niño 3.4 region from 1871 to 2008.
5

 

 y = –1.32 + 0.00169x

 r = 0.118, r2 = 0.014

 se = 0.58, cl<90%

 mean = 1.97

sd = 0.57

CV = 0.289

 median = 1.93

PCS = 0.21

na = 69

nb = 69 ⇒ z = –1.70 ⇒ nonrandom

nra = 30

 High = 3.92 (1998)

 Low = 0.66 (2003)

 50% PI = 1.97 ± 0.39

y

 mean = 25.92

sd = 0.66

CV = 0.025

 median = 25.99

PCS = –0.32

na = 69

nb = 69 ⇒ z = –2.04 ⇒ nonrandom

nra = 29

 High = 27.64 (1987)

 Low = 24.09 (1890)

 50% PI = 25.92 ± 0.45

1880 1900 1920 1940 1960 1980 2000

1.5

2.0

2.5

3.0

3.5

4.0

1.0

0.5

Year

1880 1900 1920 1940 1960 1980 2000

Year

Annual High Value—Annual Low Value

25.0

25.5

26.0

26.5

27.0

27.5

28.0

24.5

24.0

Annual Low HadSST

(a)

(b)

Figure 2. Annual and 10-yma values of (a) low values and (b) differences 

(high minus low) of HadSST in the Niño 3.4 region 

from 1871 to 2008.
6

high occurred in 1893, measuring 26.55 °C. For the lows, the highest low occurred in 1987, measuring 

27.64 °C, and the lowest low occurred in 1890, measuring 24.09 °C. The 10-yma values for both the 

annual highs and lows have recently fallen to values below their respective long-term means.

Figure 2b plots the annual difference between the high minus low values. The annual differences appear to be nonrandomly distributed, with the highest difference occurring in 1998, measuring 3.92 °C, and the lowest difference occurring in 2003, measuring 0.66 °C. The inferred regression 

is not statistically important. The 10-yma values of the differences currently remain above its longterm mean, although they appear to be decreasing with time and may soon fall below its long-term

mean.

For convenience, table 1 is included, which provides a listing of the annual means, highs, lows, 

and differences, as well as their 10-yma values and statistical aspects for each year and each grouping of SST values. Additionally, the listing identifies the month within each year when the extremes 

(lows and highs) occurred. Table 2 gives the frequency distribution of the monthly occurrences of the 

extremes. One finds that more than 80% of the time, the highest yearly value occurs in the months of 

April, May, and June, while, more than 80% of the time, the lowest yearly value occurs in the months 

of November, December, and January. Obviously, a strong seasonal effect exists within the HadSST 

data that must be removed if one seeks to correctly describe the occurrences, strengths, and durations 

of EN and LN events (i.e., any anomalies that might be embedded in the time series).

Figures 3–14 display individually the monthly values, January thru December, for the 138-yr 

history of HadSST measurements (1871–2008). The plots are constructed similar to figures 1 and 

2, giving each year’s monthly value as the thin jagged line and the 10-yma as the thick smoothed 

line, with the statistics identified for each month given to the right. Five months display nonrandom 

variations, including January, March, April, June, and July, with the remainder displaying random 

variations. Table 3 summarizes the mean and 10-yma values for each month, as well as giving various 

statistics for each month.

2.2 Monthly and 12-mma Values of HadSST in the Niño 3.4 Region (1871–2008)

Figure 15 displays the nonseasonally adjusted monthly means of HadSST for 1871–2008.27

The thin jagged line is the monthly mean and the thick smoothed line is the 12-mma value. The 

horizontal line is the mean for the entire interval (1871–2008). Clearly, the variation of the 12-mma 

values of HadSST is episodic, displaying values both lower and higher than the long-term mean. 

Cooler 12-mma values of HadSST suggest the occurrences of LN-like conditions, while warmer 

12-mma values of HadSST suggest the occurrences of EN-like conditions. Since about mid 2007, the 

12-mma values of HadSST have been cooler than the long-term mean, reflecting LN-like conditions, 

although the current trend has been upward towards warmer values (since December 2007). EN-like 

conditions seemed certain to prevail in the latter half of 2009 (HadSST monthly values have been 

published only thru April 2009, meaning that 12-mma values of HadSST can only be computed up 

thru October 2008). In fact, based on ONI, EN-like conditions, indeed, first appeared in June 2009 

and have continued through the end of the year, indicating the occurrence of an EN event, one that 

had been predicted in the earlier study.21 (ONI=1.8 °C in December 2009, a value indicative of an S 

EN event.)
7

Table 1. Annual and 10-yma values of SST in the Niño 3.4 region based on HadSST monthly 

time series from 1871 to 2008.

Year

Mean 

SST 10–yma sd L(M) 10–yma H(M) 10–yma H(M)–L(M) 10–yma Median CV PCS

1871 26.61 – 0.41 26.01(12) – 27.27(04) – 1.26 – 26.525 0.015 0.62

1872 26.35 – 0.61 25.71(12) – 27.25(05) – 1.54 – 26.08 0.023 1.33

1873 26.37 – 0.59 25.75(02) – 27.33(05) – 1.58 – 26.185 0.022 0.94

1874 25.99 – 0.61 25.33(11) – 27.00(05) – 1.67 – 25.76 0.023 1.13

1875 26.29 – 0.43 25.83(12) – 26.90(05) – 1.07 – 26.215 0.016 0.52

1876 26.56 26.74 0.52 25.56(02) 25.81 27.25(06) 27.63 1.69 1.82 26.755 0.020 –1.13

1877 28.30 26.74 0.65 26.93(01) 25.81 29.07(12) 27.71 2.14 1.90 28.56 0.023 –1.20

1878 27.62 26.80 1.30 25.83(12) 25.83 29.19(02) 27.75 3.36 1.92 28.025 0.047 –0.93

1879 26.38 26.89 0.64 25.52(11) 25.91 27.40(04) 27.82 1.88 1.92 26.32 0.024 0.28

1880 26.69 27.01 0.47 25.58(01) 26.01 27.20(04) 27.96 1.62 1.95 26.745 0.018 –0.35

1881 27.02 27.05M 0.74 26.06(11) 26.03M 28.18(04) 28.03M 2.12 2.00M 26.895 0.027 0.51

1882 26.60 26.94 0.73 25.74(11) 25.95 27.88(05) 27.94 2.14 1.99 26.395 0.027 0.84

1883 26.80 26.87m 0.52 26.12(01) 25.94m 27.54(04) 27.83m 1.42 1.89m 26.715 0.019 –0.66

1884 27.23 26.91M 0.52 26.47(01) 25.97M 28.26(05) 27.87 1.79 1.90 27.05 0.019 1.04

1885 27.44 26.89 0.41 26.70(01) 25.89 28.30(05) 27.91M 1.60 2.03 27.415 0.015 0.18

1886 26.29 26.85 0.78 25.15(12) 25.82 27.40(04) 27.89 2.25 2.07M 26.46 0.030 –0.65

1887 26.46 26.83 0.40 25.74(02) 25.79 27.12(06) 27.84 1.38 2.06 26.60 0.015 –1.05

1888 27.88 26.76 0.55 26.73(01) 25.71 28.86(11) 27.75 2.13 2.04 27.935 0.020 –0.30

1889 26.97 26.66 1.31 25.34(12) 25.62 28.56(01) 27.64 3.22 2.01 27.125 0.049 –0.35

1890 25.78 26.59m 0.84 24.09(01) 25.53m 26.87(05) 27.54m 2.78 2.01 25.74 0.033 0.14

1891 27.06 26.66 0.63 26.13(01) 25.57 27.99(05) 27.56 1.86 1.99 26.82 0.023 1.14

1892 26.23 26.73M 0.76 25.03(11) 25.66M 27.14(05) 27.64M 2.11 1.98 26.335 0.029 –0.41

1893 25.81 26.70 0.47 25.35(01)& 25.63 26.55(05) 27.62 1.20 1.98 25.595 0.018 1.37

1894 26.14 26.64m 0.50 25.49(01) 25.61m 26.87(05) 27.52m 1.38 1.91 26.09 0.019 0.30

1895 27.04 26.76 0.54 25.85(01) 25.77 27.83(05) 27.58 1.98 1.81 27.135 0.020 –0.53

1896 27.63 26.85 0.45 26.74(01) 25.91 28.16(11) 27.64 1.42 1.73m 27.775 0.016 –0.97

1897 27.13 26.93 0.75 26.04(11) 25.97 28.07(01) 27.70 2.03 1.73m 27.42 0.028 –1.16

1898 26.50 27.07 0.53 25.80(12) 26.03 27.40(06) 27.86 1.60 1.82 26.435 0.020 0.37

1899 27.27 27.18 0.73 25.83(01) 26.06 28.09(12) 27.99 2.26 1.93 27.47 0.027 –0.82

1900 27.80 27.27 0.57 26.79(11) 26.15 28.45(06) 28.10 1.66 1.95 27.98 0.021 –0.95

1901 26.94 27.28M 0.55 26.24(12) 26.18M 27.68(05) 28.16M 1.44 1.98 26.995 0.020 –0.30

1902 27.80 27.23 0.82 26.08(01) 26.13 28.67(07) 28.13 2.59 2.00M 28.11 0.029 –1.13

1903 27.06 27.21 0.95 25.57(12) 26.11 28.13(04) 28.10 2.56 1.99m 27.215 0.035 –0.49

1904 27.05 27.16 0.71 25.84(01) 26.06 27.98(07) 28.07 2.14 2.01M 27.235 0.026 –0.78

1905 27.95 27.02 0.45 27.26(01) 25.96 28.94(05) 27.95 1.68 2.00 27.985 0.016 –0.23

1906 27.03 26.93 0.88 25.87(10) 25.88 28.22(04) 27.86 2.35 1.98 27.085 0.033 –0.19

1907 26.69 26.90 0.44 26.01(01) 25.87m 27.39(05) 27.83 1.38 1.97 26.585 0.016 0.72

1908 26.55 26.88m 0.62 25.43(12) 25.91 27.47(06) 27.79m 2.04 1.88 26.535 0.023 0.07

1909 26.19 26.90M 0.69 25.15(11) 26.01 27.50(05) 27.79m 2.35 1.78m 26.06 0.026 0.57

1910 26.13 26.90 0.38 25.46(09) 26.02M 26.65(06) 27.80M 1.19 1.79 26.125 0.015 0.04

1911 26.81 26.83 0.47 26.01(01) 25.93 27.55(12) 27.77 1.54 1.84 26.875 0.018 –0.41

1912 27.28 26.78m 0.72 26.10(12) 25.83 28.35(04) 27.75m 2.25 1.92 27.28 0.026 0.00

1913 27.10 26.81 0.38 26.38(01) 25.80m 27.58(05) 27.79 1.20 2.00 27.04 0.014 0.47

1914 27.56 26.91 0.42 26.96(11) 25.87 28.46(04) 27.87 1.50 2.00 27.57 0.015 –0.07

1915 27.42 27.05 0.75 26.36(12) 25.98 28.78(06) 27.99 2.42 2.01 27.35 0.027 0.28

1916 26.13 27.09M 0.94 24.93(11) 26.02M 27.64(05) 28.05M 2.71 2.03 26.14 0.036 –0.13
8

Table 1. Annual and 10-yma values of SST in the Niño 3.4 region based on HadSST monthly 

time series from 1871 to 2008 (Continued). 

Year

Mean 

SST 10–yma sd L(M) 10–yma H(M) 10–yma H(M)–L(M) 10–yma Median CV PCS

1917 26.64 27.06 0.83 25.02(01) 25.99 27.65(06) 28.03 2.63 2.04 26.695 0.031 –0.20

1918 27.14 27.03 0.78 25.74(01) 25.97 28.06(06) 28.02 2.32 2.05 27.185 0.029 –0.17

1919 27.67 26.98 0.71 26.29(11) 25.88 28.49(05) 27.99 2.20 2.11 27.815 0.026 –0.61

1920 27.28 26.93m 0.44 26.57(11)* 25.77m 27.98(06) 27.92m 1.41 2.15M 27.295 0.016 –0.10

1921 26.61 26.99 0.56 25.62(11) 25.80 27.47(06) 27.95 1.85 2.15M 26.68 0.021 –0.38

1922 26.73 27.08 0.63 26.04(01) 25.97 28.09(05) 28.00M 2.05 2.05 26.585 0.024 0.69

1923 27.09 27.09M 0.58 26.00(02) 26.07 27.62(05) 27.99 1.62 1.92 27.31 0.021 –1.14

1924 26.66 27.06 0.74 25.56(11) 26.11 27.75(04) 27.94 2.19 1.83 26.65 0.028 0.04

1925 27.25 27.06m 0.72 25.55(01) 26.14 28.19(12) 27.93m 2.64 1.79m 27.515 0.026 –1.10

1926 27.58 27.13 0.96 26.34(10) 26.19 28.78(04) 28.02 2.44 1.82 27.96 0.035 –1.19

1927 26.99 27.19M 0.32 26.60(09) 26.23M 27.54(06) 28.08 0.94 1.85 26.96 0.012 0.28

1928 27.00 27.17 0.44 26.49(11) 26.21 27.83(05) 28.09M 1.34 1.89 26.99 0.016 0.07

1929 27.15 27.14 0.41 26.43(01) 26.18m 27.81(06) 28.08 1.38 1.90M 27.12 0.015 0.22

1930 27.78 27.11 0.42 26.93(01) 26.22 28.44(11) 28.02 1.51 1.81 27.865 0.015 –0.61

1931 27.51 27.08 0.94 26.31(12) 26.26M 28.73(04) 27.95 2.42 1.69 27.85 0.034 –1.09

1932 27.06 27.06 0.69 26.16(01) 26.26M 28.14(05) 27.94m 1.98 1.68m 26.87 0.025 0.83

1933 26.44 27.04 0.76 25.38(12) 26.21 27.78(04) 27.96 2.40 1.75 26.46 0.029 –0.08

1934 26.57 27.01 0.56 25.64(01) 26.14 27.37(05) 27.96 1.73 1.82 26.51 0.021 0.32

1935 26.89 27.00m 0.36 26.26(01) 26.10m 27.45(04) 27.96 1.19 1.86M 26.935 0.013 –0.38

1936 27.17 27.03 0.46 26.55(08) 26.15 28.06(04) 27.99 1.51 1.84m 27.235 0.017 –0.42

1937 27.07 27.04M 0.47 26.27(01) 26.16M 27.98(04) 28.02 1.71 1.86 26.995 0.017 0.48

1938 26.60 27.02m 0.67 25.79(12) 26.11m 27.86(04) 28.02 2.07 1.92M 26.42 0.025 0.81

1939 26.87 27.05M 0.66 25.81(02) 26.13 27.74(06) 28.04 1.93 1.91m 26.96 0.025 –0.41

1940 27.80 27.05 0.56 26.80(09) 26.14M 28.57(04) 28.07M 1.77 1.93 27.87 0.020 –0.38

1941 28.17 27.01 0.58 27.43(09) 26.10 29.18(05) 28.06 1.75 1.96 27.95 0.021 1.14

1942 26.61 26.98m 1.08 25.15(11) 26.05 28.34(04) 28.04m 3.19 1.99 26.92 0.041 –0.86

1943 26.55 26.99 0.72 25.38(01) 26.04 27.58(06) 28.04m 2.20 2.01 26.405 0.027 0.60

1944 26.96 27.00M 0.65 26.15(01) 26.03 28.00(05) 28.07M 1.85 2.04 26.90 0.024 0.28

1945 26.44 26.90 0.50 25.87(10) 25.92 27.41(05) 27.99 1.54 2.07 26.26 0.019 0.36

1946 26.85 26.76 0.51 26.14(01) 25.75 27.83(06) 27.84 1.69 2.10M 26.67 0.019 1.06

1947 26.80 26.72m 0.70 25.70(09) 25.69m 27.75(06) 27.78m 2.05 2.08 26.80 0.026 0.00

1948 27.14 26.78 0.68 26.06(10) 25.81 28.17(05) 27.82 2.11 2.01 27.045 0.025 0.42

1949 26.57 26.80M 0.83 25.33(11) 25.84M 27.96(04) 27.84M 2.63 2.00m 26.63 0.031 –0.22

1950 26.00 26.74 0.56 25.26(02) 25.75 26.86(04) 27.78 1.60 2.03 26.02 0.022 –0.11

1951 27.19 26.68m 0.78 25.45(01) 25.66 27.88(07) 27.73m 2.43 2.07 27.47 0.029 –1.08

1952 26.88 26.69 0.59 26.04(12) 25.63m 28.28(04) 27.73m 2.24 2.09M 26.835 0.022 0.23

1953 27.38 26.74 0.60 26.74(12) 25.67 28.54(04) 27.76 1.80 2.09M 27.21 0.022 0.85

1954 26.48 26.79 0.74 25.49(11) 25.73 27.45(04) 27.77 1.96 2.04 26.54 0.028 –0.24

1955 25.88 26.86 0.67 24.75(11) 25.83 26.82(04) 27.82 2.07 2.00 25.94 0.026 –0.27

1956 26.20 26.89M 0.58 25.35(01) 25.91 27.28(05) 27.88M 1.93 1.97 26.05 0.022 0.78

1957 27.55 26.87 0.65 26.02(01) 25.94M 28.31(05) 27.84 2.29 1.90 27.70 0.024 –0.69

1958 27.49 26.86m 0.70 26.44(09) 25.92 28.25(03) 27.77 1.81 1.85 27.625 0.025 –0.58

1959 27.05 26.87 0.58 26.22(09) 25.89m 28.04(04) 27.73m 1.82 1.84m 26.98 0.021 0.36

1960 26.97 26.96 0.52 26.27(11) 25.96 27.92(05) 27.80 1.65 1.85 26.83 0.019 0.81

1961 26.87 27.10 0.66 26.02(10) 26.07 27.90(04) 27.93 1.88 1.86M 26.71 0.025 0.73

1962 26.73 27.11M 0.51 26.09(12) 26.11M 27.47(06) 27.95M 1.38 1.84 26.67 0.019 0.35
9

Table 1. Annual and 10-yma values of SST in the Niño 3.4 region based on HadSST monthly 

time series from 1871 to 2008 (Continued). 

Year

Mean 

SST 10–yma sd L(M) 10–yma H(M) 10–yma H(M)–L(M) 10–yma Median CV PCS

1963 27.42 27.05m 0.53 26.26(01) 26.09m 27.95(07) 27.90 1.69 1.81 27.60 0.019 –1.02

1964 26.52 27.05 0.73 25.52(12) 26.12 27.33(01) 27.89m 1.81 1.77m 26.695 0.028 –0.72

1965 27.66 27.07M 0.77 26.01(01) 26.13M 28.34(10) 27.90M 2.33 1.77m 28.035 0.028 –1.46

1966 27.29 27.02m 0.70 26.28(11) 26.04 28.31(04) 27.86m 2.03 1.82 27.52 0.026 –0.99

1967 26.68 27.04 0.57 26.02(01) 25.99 27.63(05) 27.88 1.61 1.89 26.46 0.021 1.16

1968 27.04 27.04M 0.60 25.98(01) 25.89 27.87(06) 27.96M 1.89 2.06 27.25 0.022 –1.05

1969 27.62 26.97 0.35 27.22(09) 25.75 28.25(05) 27.96M 1.03 2.20 27.44 0.013 1.54

1970 26.71 26.87 0.88 25.47(12) 25.65 27.95(04) 27.88 2.48 2.23 26.685 0.033 0.09

1971 26.13 26.77m 0.60 25.11(01) 25.53 27.04(05) 27.80 1.93 2.27 25.98 0.023 0.75

1972 27.84 26.80 0.86 26.00(01) 25.51m 28.78(12) 27.79 2.78 2.28M 28.12 0.031 –0.98

1973 26.41 26.83M 1.37 24.41(12) 25.57M 28.18(01) 27.78 3.77 2.21 26.455 0.052 –0.10

1974 26.12 26.81m 0.75 24.56(01) 25.55m 27.07(05) 27.74 2.51 2.20 26.19 0.029 –0.28

1975 26.02 26.81 0.73 24.95(12) 25.58 27.18(04) 27.73m 2.23 2.16 26.10 0.028 –0.33

1976 26.98 26.88 0.88 24.78(01) 25.69 27.69(06) 27.77 2.91 2.09 27.335 0.033 –1.21

1977 27.56 26.92 0.27 27.13(08) 25.76 28.05(06) 27.82 0.92 2.05 27.635 0.010 –0.83

1978 26.88 26.98 0.48 26.15(09) 25.85 27.40(04) 27.87 1.25 2.02 26.99 0.018 –0.69

1979 27.25 27.05M 0.39 26.63(01) 25.93 27.94(04) 27.91M 1.31 1.99 27.16 0.014 0.69

1980 27.20 27.07m 0.54 26.63(09)* 25.99 28.05(06) 27.91M 1.42 1.92 27.11 0.020 0.50

1981 26.87 27.10 0.54 26.12(01) 26.07 27.76(05) 27.90m 1.64 1.83 26.70 0.020 0.94

1982 27.98 27.15M 0.81 26.54(01) 26.15M 28.92(12) 27.95 2.38 1.80m 28.075 0.029 –0.35

1983 27.51 27.14 1.48 25.52(11) 26.09 29.01(01) 28.00M 3.49 1.90 27.71 0.054 –0.41

1984 26.34 27.05 0.68 25.05(12) 25.91 27.22(05) 27.96 2.17 2.05 26.435 0.026 –0.42

1985 26.35 27.00m 0.41 25.69(01) 25.81m 26.97(05) 27.92m 1.28 2.11 26.26 0.016 0.66

1986 27.15 27.04 0.62 25.79(01) 25.85 27.70(11) 27.96 1.91 2.11 27.37 0.023 –1.06

1987 28.29 27.07M 0.41 27.64(12) 25.88 28.92(06) 28.00 1.28 2.12M 28.32 0.014 –0.22

1988 26.04 27.05m 1.14 24.48(11) 25.94 27.54(03) 28.00 3.06 2.06 25.96 0.044 0.21

1989 26.27 27.11 0.69 24.63(01) 26.08 27.06(05) 28.03 2.43 1.95m 26.365 0.026 –0.41

1990 27.24 27.20 0.51 26.60(01) 26.17 28.19(05) 28.12 1.59 1.96 27.085 0.019 0.91

1991 27.66 27.21M 0.49 26.98(09) 26.18M 28.34(06) 28.17 1.36 1.99 27.715 0.018 –0.34

1992 27.69 27.18m 1.08 26.39(10) 26.11 29.18(04) 28.17 2.79 2.06 27.845 0.039 –0.43

1993 27.50 27.24 0.72 26.77(12) 26.07m 28.79(05) 28.25 2.02 2.18 27.135 0.026 1.52

1994 27.44 27.28M 0.48 26.60(02) 26.12M 28.00(05) 28.32M 1.40 2.20 27.515 0.017 –0.47

1995 27.04 27.21 0.88 25.86(12) 26.05 28.04(04) 28.26 2.18 2.21 27.45 0.033 –1.40

1996 26.69 27.11 0.57 25.93(01) 25.90 27.57(06) 28.17 1.64 2.27M 26.52 0.021 0.89

1997 28.25 27.06 1.04 26.15(01) 25.83m 29.08(11) 28.09 2.93 2.26 28.835 0.037 –1.69

1998 27.14 27.05 1.54 25.08(12) 25.84 29.00(01) 27.99 3.92 2.15 26.895 0.057 0.48

1999 25.97 27.04m 0.72 25.04(12) 25.86 26.99(05) 27.92m 1.95 2.06m 25.90 0.028 0.29

2000 26.19 27.04 0.71 24.79(01) 25.87M 27.07(05) 27.93 2.28 2.06m 26.27 0.027 –0.34

2001 26.73 27.07M 0.62 25.70(01) 25.85 27.58(06) 27.94M 1.88 2.09 26.625 0.023 0.51

2002 27.65 27.00 0.56 26.44(01) 25.78 28.37(06) 27.88 1.93 2.10M 27.845 0.020 –1.04

2003 27.30 26.88 0.31 26.90(09) 25.71 27.56(01) 27.72 0.66 2.01 27.355 0.011 –0.53

2004 27.43 – 0.35 26.84(01) – 27.96(05) – 1.12 – 27.44 0.013 –0.09

2005 27.10 – 0.73 25.83(12) – 28.16(05) – 2.33 – 27.08 0.027 0.08

2006 27.16 – 0.71 25.60(01) – 27.78(06) – 2.18 – 27.425 0.026 –1.12

2007 26.50 – 0.99 24.98(12) – 27.61(04) – 2.63 – 26.87 0.037 –1.12
10

Table 1. Annual and 10-yma values of SST in the Niño 3.4 region based on HadSST monthly 

time series from 1871 to 2008 (Continued). 

Year

Mean 

SST 10–yma sd L(M) 10–yma H(M) 10–yma H(M)–L(M) 10–yma Median CV PCS

2008 26.35 – 0.82 24.79(01) – 27.24(06) – 2.45 – 26.45 0.031 –0.37

2009 – – – – – – – – – – – –

Statistics (Based on 1871–2008)

Mean SST L(M) H(M) H(M)–L(M)

mean

sd

low

high

H–L

median

na

nb

nra

z

random?

±50% PI

CV

PCS

26.95

0.57

25.78(1890)

28.30(1877)

2.52

26.985

69

69

28

–2.38

no

0.39

0.021

–0.18

25.92

0.66

24.09(1890)

27.64(1987)

3.55

25.99

69

69

29

–2.04

no

0.45

0.025

–0.32

27.87

0.58

26.55(1893)

29.19(1878)

2.64

27.865

69

69

33

–0.68

yes

0.39

0.021

0.03

1.97

0.57

0.66(2003)

3.92(1998)

3.26

1.93

69

69

30

–1.70

yes

0.39

0.289

0.21

Notes: Mean SST = monthly mean sea surface temperature in the year, based on the Hadley dataset and measured in degrees Celsius.

sd = standard deviation.

L(M) = lowest monthly value in the year and the month it occurs.

H(M) = highest monthly value in the year and the month it occurs.

H–L = range.

na = number of yearly values above the median.

nb = number of yearly values below the median.

nra = number of runs above the median value.

z = normal deviate calculated from nra, na and nb; when z <–1.96 or >1.96, hypothesis testing suggests that the distribution is nonrandom.

PI = prediction interval.

CV = coefficient of variation, equal to sd/Mean SST.

PCS = Pearson coefficient of skewness, equal to 3(Mean SST – Median)/sd.

* = also following month.

& = also seen in November 1893.

M refers to local maximum values within a string of yearly values.

m refers to local minimum values within a string of yearly values.

Table 2. Frequency of occurrence of monthly high and low values of SST in the Niño 3.4 region

based on HadSST values from 1871 to 2008.

Monthly High Value 

Occurrence

Monthly Low Value 

Occurrence

Month f Percent f Percent

01

02

03

04

05

06

07

08

09

10

11

12

Total

7

1

2

36

47

29

4

0

0

1

5

6

138

0.051

0.007

0.014

0.261

0.341

0.210

0.029

0.000

0.000

0.007

0.036

0.043

100.000

58

7

0

0

0

0

0

2

12

6

23

30

138

0.420

0.051

0.000

0.000

0.000

0.000

0.000

0.014

0.087

0.043

0.167

0.217

1.000
11

 mean = 26.54

sd = 0.95

CV = 0.036

 median = 26.365

PCS = 0.55

na = 69

nb = 69 ⇒ z = 2.04 ⇒ nonrandom

nra = 29

 High = 29.01 (1983)

 Low = 24.09 (1890)

 50% PI = 26.54 ± 0.64

1880 1900 1920 1940 1960 1980 2000

24.5

25.0

25.5

26.0

26.5

27.0

27.5

28.0

28.5

29.0

29.5

24.0

Year

HadSST

Figure 3. Annual and 10-yma values of January values of HadSST 

in the Niño 3.4 region from 1871 to 2009.
12

 mean = 26.72

sd = 0.83

CV = 0.031

 median = 26.655

PCS = 0.23

na = 69

nb = 69 ⇒ z = –0.34 ⇒ random

nra = 34

 High = 29.19 (1878)

 Low = 24.65 (1890)

 50% PI = 26.72 ± 0.56

1880 1900 1920 1940 1960 1980 2000

24.5

25.0

25.5

26.0

26.5

27.0

27.5

28.0

28.5

29.0

29.5

24.0

Year

HadSST

Figure 4. Annual and 10-yma values of February values of HadSST 

in the Niño 3.4 region from 1871 to 2009.
13

 mean = 27.13

sd = 0.70

CV = 0.026

 median = 27.155

PCS = –0.11

na = 69

nb = 69 ⇒ z = –2.04 ⇒ nonrandom

nra = 29

 High = 28.95 (1983)

 Low = 25.75 (1874)

 50% PI = 27.13 ± 0.47

1880 1900 1920 1940 1960 1980 2000

24.5

25.0

25.5

26.0

26.5

27.0

27.5

28.0

28.5

29.0

29.5

24.0

Year

HadSST

Figure 5. Annual and 10-yma values of March values of HadSST 

in the Niño 3.4 region from 1871 to 2008.
14

 mean = 27.64

sd = 0.58

CV = 0.021

 median = 27.61

PCS = 0.16

na = 70

nb = 68 ⇒ z = –1.70 ⇒ nonrandom

nra = 30

 High = 29.18 (1992)

 Low = 26.47 (1893)

 50% PI = 27.64 ± 0.39

1880 1900 1920 1940 1960 1980 2000

24.5

25.0

25.5

26.0

26.5

27.0

27.5

28.0

28.5

29.0

29.5

24.0

Year

HadSST

Figure 6. Annual and 10-yma values of April values of HadSST 

in the Niño 3.4 region from 1871 to 2008.
15

 mean = 27.69

sd = 0.57

CV = 0.021

median = 27.685

PCS = 0.03

na = 69

nb = 69 ⇒ z = –0.68 ⇒ random

nra = 33

 High = 29.18 (1941)

 Low = 26.46 (1910)

 50% PI = 27.69 ± 0.39

1880 1900 1920 1940 1960 1980 2000

24.5

25.0

25.5

26.0

26.5

27.0

27.5

28.0

28.5

29.0

29.5

24.0

Year

HadSST

Figure 7. Annual and 10-yma values of May values of HadSST 

in the Niño 3.4 region from 1871 to 2008.
16

 mean = 27.56

sd = 0.55

CV = 0.020

 median = 27.54

PCS = 0.11

na = 70

nb = 68 ⇒ z = –2.04 ⇒ nonrandom

nra = 29

 High = 29.92 (1987)

 Low = 26.23 (1988)

 50% PI = 27.56 ± 0.37

1880 1900 1920 1940 1960 1980 2000

24.5

25.0

25.5

26.0

26.5

27.0

27.5

28.0

28.5

29.0

29.5

24.0

Year

HadSST

Figure 8. Annual and 10-yma values of June values of HadSST 

in the Niño 3.4 region from 1871 to 2008.
17

 mean = 27.07

sd = 0.60

CV = 0.022

median = 27.08

PCS = –0.05

na = 70

nb = 68 ⇒ z = –1.70 ⇒ nonrandom

nra = 30

 High = 28.83 (1997)

 Low = 25.69 (1988)

 50% PI = 27.07 ± 0.41

1880 1900 1920 1940 1960 1980 2000

24.5

25.0

25.5

26.0

26.5

27.0

27.5

28.0

28.5

29.0

29.5

24.0

Year

HadSST

Figure 9. Annual and 10-yma values of July values of HadSST 

in the Niño 3.4 region from 1871 to 2008.
18

 mean = 26.76

sd = 0.66

CV = 0.025

median = 26.72

PCS = 0.18

na = 69

nb = 69 ⇒ z = –0.68 ⇒ random

nra = 33

 High = 28.81 (1997)

 Low = 25.39 (1916)

 50% PI = 26.76 ± 0.45

1880 1900 1920 1940 1960 1980 2000

24.5

25.0

25.5

26.0

26.5

27.0

27.5

28.0

28.5

29.0

29.5

24.0

Year

HadSST

Figure 10. Annual and 10-yma values of August values of HadSST 

in the Niño 3.4 region from 1871 to 2008.
19

 mean = 26.62

sd = 0.72

CV = 0.027

 median = 26.58

PCS = 0.17

na = 70

nb = 68 ⇒ z = –1.02 ⇒ random

nra = 32

 High = 28.85 (1997)

 Low = 25.31 (1975)

 50% PI = 26.62 ± 0.49

1880 1900 1920 1940 1960 1980 2000

24.5

25.0

25.5

26.0

26.5

27.0

27.5

28.0

28.5

29.0

29.5

24.0

Year

HadSST

Figure 11. Annual and 10-yma values of September values of HadSST 

in the Niño 3.4 region from 1871 to 2008.
20

 mean = 26.63

sd = 0.84

CV = 0.032

 median = 26.51

PCS = 0.14

na = 70

nb = 68 ⇒ z = –0.68 ⇒ random

nra = 33

 High = 29.02 (1997)

 Low = 24.65 (1988)

 50% PI = 26.63 ± 0.57

1880 1900 1920 1940 1960 1980 2000

24.5

25.0

25.5

26.0

26.5

27.0

27.5

28.0

28.5

29.0

29.5

24.0

Year

HadSST

Figure 12. Annual and 10-yma values of October values of HadSST 

in the Niño 3.4 region from 1871 to 2008.
21

 mean = 26.53

sd = 0.95

CV = 0.036

 median = 26.385

PCS = 0.46

na = 69

nb = 69 ⇒ z = –0.34 ⇒ random

nra = 34

 High = 29.08 (1997)

 Low = 24.48 (1988)

 50% PI = 26.53 ± 0.64

1880 1900 1920 1940 1960 1980 2000

24.5

25.0

25.5

26.0

26.5

27.0

27.5

28.0

28.5

29.0

29.5

24.0

Year

HadSST

Figure 13. Annual and 10-yma values of November values of HadSST 

in the Niño 3.4 region from 1871 to 2008.
22

 mean = 26.54

sd = 0.97

CV = 0.037

 median = 26.40

PCS = 0.43

na = 69

nb = 69 ⇒ z = –1.02 ⇒ random

nra = 32

 High = 29.07 (1877)

 Low = 24.41 (1973)

 50% PI = 26.54 ± 0.66

1880 1900 1920 1940 1960 1980 2000

24.5

25.0

25.5

26.0

26.5

27.0

27.5

28.0

28.5

29.0

29.5

24.0

Year

HadSST

Figure 14. Annual and 10-yma values of December values of HadSST 

in the Niño 3.4 region from 1871 to 2008.
23

Table 3. HadSST monthly and 10-yma values for the Niño 3.4 region from 1871 to April 2009.

Year

January February March April May June July August September October November December

Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma

1871 26.33 – 26.18 – 26.83 – 27.27 – 27.16 – 27.16 – 26.62 – 26.54 – 26.51 – 26.40 – 26.35 – 26.01 –1872 25.86 – 26.14 – 26.76 – 27.00 – 27.25 – 27.16 – 26.91 – 26.02 – 25.73 – 25.79 – 25.86 – 25.71 –1873 25.79 – 25.75 – 25.95 – 27.10 – 27.33 – 27.21 – 26.65 – 26.48 – 26.41 – 25.96 – 25.88 – 25.89 –1874 25.64 – 25.70 – 25.85 – 26.83 – 27.00 – 26.96 – 26.22 – 25.82 – 25.62 – 25.49 – 25.33 – 25.45 –1875 25.87 – 26.39 – 26.66 – 26.90 – 26.77 – 26.92 – 26.37 – 26.06 – 25.84 – 25.90 – 26.01 – 25.83 –1876 25.63 26.29 25.56 26.51 26.13 26.86 26.59 27.37 26.78 27.42 27.25 27.44 26.88 26.91 26.71 26.57 26.73 26.44 26.85 26.39 26.80 26.32 26.81 26.301877 26.93 26.33 27.22 26.56 27.78 26.89 28.27 27.46 28.62 27.50 28.67 27.49 28.64 26.91 28.42 26.61 28.50 26.46 28.68 26.40 28.74 26.30 29.07 26.321878 28.99 26.36 29.19 26.59 28.57 26.94 28.69 27.53 28.69 27.54 28.61 27.51 27.48 26.93 26.76 26.65 26.43 26.49 26.20 26.44 25.95 26.32 25.83 26.351879 26.03 26.42 26.58 26.67 27.02 27.05 27.40 27.61 27.03 27.61 27.02 27.55 26.46 27.02 26.18 26.73 25.93 26.57 25.80 26.53 25.52 26.46 25.56 26.461880 25.58 26.50 26.03 26.75 26.63 27.16 27.20 27.71 27.15 27.75 27.08 27.63 26.70 27.13 26.63 26.85 26.72 26.70 26.90 26.68 26.90 26.58 26.77 26.621881 26.87 26.60 26.99 26.84 27.58 27.25 28.18 27.79 28.03 27.84 27.92 27.65 26.96 27.15 26.71 26.87 26.42 26.72 26.31 26.70 26.06 26.58 26.22 26.621882 26.13 26.61 26.21 26.82 26.73 27.21 27.87 27.75 27.88 27.75 27.29 27.55 26.65 27.02 26.55 26.72 26.24 26.55 26.08 26.53 25.74 26.40 25.83 26.421883 26.12 26.44 26.27 26.66 26.86 27.08 27.54 27.63 27.49 27.64 27.48 27.45 27.21 26.94 26.85 26.66 26.58 26.49 26.32 26.53 26.43 26.45 26.44 26.431884 26.47 26.45 26.75 26.65 27.26 27.09 28.03 27.64 28.26 27.68 27.55 27.46 27.51 26.95 27.08 26.70 26.94 26.53 27.02 26.61 26.95 26.59 26.93 26.541885 26.70 26.51 27.03 26.67 27.38 27.12 27.75 27.66 28.30 27.72 27.85 27.48 27.30 26.93 27.21 26.62 27.27 26.47 27.45 26.51 27.46 26.53 27.61 26.491886 26.75 26.40 26.67 26.57 27.15 27.07 27.40 27.62 27.02 27.71 26.79 27.47 26.25 26.93 25.85 26.58 25.54 26.41 25.59 26.46 25.31 26.50 25.15 26.461887 25.90 26.36 25.74 26.56 26.08 27.05 26.59 27.57 26.72 27.67 27.12 27.47 26.68 26.95 26.25 26.58 26.41 26.40 26.61 26.44 26.69 26.49 26.74 26.461888 26.73 26.31 27.42 26.54 27.66 27.00 28.07 27.47 28.34 27.59 28.09 27.41 27.78 26.88 27.80 26.50 27.33 26.32 28.16 26.35 28.86 26.41 28.26 26.401889 28.56 26.23 28.24 26.45 28.09 26.91 28.23 27.36 28.19 27.47 27.78 27.32 26.47 26.76 25.88 26.38 25.83 26.20 25.42 26.24 25.57 26.29 25.34 26.311890 24.09 26.14 24.65 26.35 26.11 26.83 26.63 27.30 26.87 27.38 26.82 27.27 26.30 26.68 25.50 26.33 25.46 26.13 25.47 26.17 25.58 26.21 25.90 26.241891 26.13 26.09 26.51 26.33 27.19 26.82 27.92 27.31 27.99 27.39 27.97 27.29 27.34 26.73 26.93 26.44 26.67 26.23 26.70 26.26 26.71 26.34 26.60 26.371892 26.08 26.20 26.42 26.44 26.68 26.92 27.12 27.37 27.14 27.48 27.12 27.35 26.60 26.83 26.25 26.57 25.68 26.35 25.19 26.35 25.03 26.45 25.41 26.491893 25.35 26.28 25.60 26.49 26.02 26.94 26.47 27.37 26.55 27.48 26.50 27.34 25.91 26.81 25.58 26.50 25.48 26.32 25.37 26.24 25.35 26.27 25.59 26.341894 25.49 26.11 25.63 26.32 26.20 26.81 26.85 27.29 26.87 27.41 26.85 27.31 26.34 26.78 26.07 26.50 25.65 26.35 25.91 26.26 25.73 26.25 26.11 26.351895 25.85 26.17 26.28 26.38 26.86 26.85 27.60 27.34 27.83 27.47 27.47 27.39 26.96 26.90 27.23 26.69 27.17 26.51 27.05 26.46 27.10 26.42 27.07 26.551896 26.74 26.42 26.85 26.58 27.41 26.96 27.76 27.42 27.82 27.53 27.48 27.44 27.66 26.97 27.92 26.78 27.79 26.59 27.83 26.53 28.16 26.46 28.14 26.601897 28.07 26.49 27.90 26.61 27.80 26.98 27.55 27.44 27.69 27.58 27.66 27.48 27.29 27.05 26.73 26.85 26.51 26.70 26.17 26.66 26.04 26.60 26.19 26.711898 26.07 26.62 26.19 26.72 26.47 27.10 27.16 27.57 27.28 27.70 27.40 27.62 26.59 27.24 26.11 26.99 26.56 26.86 26.40 26.86 26.00 26.78 25.80 26.841899 25.83 26.76 26.05 26.84 26.69 27.21 27.43 27.66 27.90 27.79 27.78 27.74 27.20 27.32 27.51 27.10 27.18 26.95 27.66 26.99 27.94 26.86 28.09 26.901900 27.99 26.85 28.06 26.92 28.25 27.29 28.43 27.70 28.40 27.87 28.45 27.83 27.97 27.45 27.65 27.21 27.31 27.06 27.15 27.12 26.79 26.94 27.19 27.011901 27.40 26.96 27.06 27.00 27.30 27.39 27.64 27.74 27.68 27.93 27.43 27.89 26.93 27.46 26.50 27.17 26.45 27.02 26.42 27.06 26.26 26.86 26.24 26.941902 26.08 26.89 26.50 26.96 26.99 27.37 27.97 27.75 28.34 27.92 28.45 27.89 28.67 27.38 28.09 27.07 28.19 26.94 28.13 26.98 28.19 26.79 27.98 26.851903 27.91 26.80 27.69 26.91 28.05 27.33 28.13 27.73 27.77 27.91 27.98 27.87 26.74 27.35 26.55 27.07 26.15 26.94 26.31 26.98 25.89 26.80 25.57 26.841904 25.84 26.83 25.97 26.94 26.40 27.34 27.05 27.76 27.47 27.90 27.83 27.82 27.98 27.31 27.42 27.00 26.76 26.86 27.65 26.87 26.81 26.65 27.44 26.701905 27.26 26.74 27.48 26.83 28.18 27.25 28.06 27.61 28.94 27.78 28.28 27.67 28.05 27.18 27.92 26.84 28.18 26.71 27.85 26.69 27.48 26.48 27.76 26.511906 27.47 26.55 27.44 26.69 28.06 27.12 28.22 27.47 27.88 27.64 27.83 27.56 26.73 27.10 26.51 26.76 25.94 26.64 25.87 26.65 26.33 26.50 26.07 26.511907 26.01 26.58 26.36 26.70 26.83 27.12 27.21 27.44 27.39 27.57 27.28 27.49 26.68 27.02 26.22 26.69 26.88 26.60 26.48 26.60 26.40 26.50 26.49 26.481908 26.30 26.61 26.83 26.72 26.63 27.14 27.22 27.40 27.41 27.54 27.47 27.42 26.59 26.96 26.48 26.62 26.23 26.56 26.23 26.54 25.78 26.51 25.43 26.481909 26.29 26.61 25.88 26.76 26.72 27.17 27.09 27.42 27.50 27.55 26.59 27.39 26.22 26.97 25.90 26.65 25.90 26.63 25.49 26.53 25.15 26.59 25.51 26.561910 25.65 26.69 26.12 26.83 26.46 27.21 26.59 27.50 26.46 27.54 26.65 27.41 26.35 26.92 25.98 26.62 25.46 26.60 25.80 26.46 26.13 26.55 25.95 26.49
24Table 3. HadSST monthly and 10-yma values for the Niño 3.4 region from 1871 to April 2009 (Continued).

Year

January February March April May June July August September October November December

Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma

1911 26.01 26.65 26.18 26.77 26.44 27.12 26.66 27.45 26.82 27.50 27.05 27.41 27.01 26.85 26.59 26.51 26.97 26.51 26.93 26.39 27.50 26.43 27.55 26.36

1912 28.13 26.55 27.59 26.66 27.95 27.04 28.35 27.41 27.87 27.50 27.44 27.41 27.12 26.85 26.48 26.50 26.85 26.48 26.60 26.38 26.82 26.35 26.10 26.271913 26.38 26.47 26.94 26.58 27.42 27.01 27.00 27.42 27.58 27.52 27.53 27.45 27.08 26.90 26.79 26.56 26.80 26.51 26.76 26.46 27.45 26.45 27.43 26.371914 27.28 26.54 27.56 26.64 27.58 27.07 28.46 27.49 27.87 27.59 27.77 27.57 27.75 27.00 27.80 26.67 27.43 26.63 26.99 26.60 26.96 26.61 27.27 26.561915 27.46 26.71 27.41 26.81 27.75 27.21 28.24 27.61 28.38 27.70 28.78 27.72 27.29 27.12 26.93 26.80 26.92 26.78 26.97 26.74 26.51 26.69 26.36 26.661916 26.46 26.84 26.16 26.87 26.72 27.24 27.14 27.69 27.64 27.76 27.32 27.81 26.12 27.17 25.39 26.85 25.39 26.83 25.37 26.81 24.93 26.62 24.95 26.621917 25.02 26.78 25.56 26.83 26.62 27.18 27.48 27.66 27.57 27.78 27.65 27.82 27.18 27.15 27.03 26.83 26.73 26.79 26.77 26.79 26.23 26.50 25.87 26.541918 25.74 26.67 25.94 26.74 26.30 27.10 27.21 27.62 27.70 27.79 28.06 27.81 27.15 27.13 27.00 26.83 27.16 26.80 27.66 26.82 27.89 26.48 27.89 26.551919 28.18 26.65 28.00 26.69 28.16 27.05 28.46 27.59 28.49 27.75 28.29 27.77 27.63 27.05 27.50 26.76 27.26 26.75 26.87 26.83 26.29 26.42 26.93 26.491920 27.22 26.54 27.37 26.62 27.79 27.01 27.61 27.51 27.66 27.67 27.98 27.67 27.37 27.00 27.01 26.70 27.02 26.70 27.22 26.82 26.57 26.40 26.57 26.521921 27.01 26.53 26.25 26.66 25.84 27.04 27.22 27.54 26.94 27.67 27.47 27.66 26.95 27.11 26.59 26.81 26.58 26.80 26.77 26.90 25.62 26.53 26.09 26.681922 26.04 26.69 26.69 26.83 27.33 27.15 27.23 27.62 28.09 27.71 27.25 27.70 26.78 27.18 26.09 26.88 26.38 26.86 26.48 26.96 26.34 26.63 26.06 26.801923 26.17 26.84 26.00 26.95 26.41 27.21 27.22 27.64 27.62 27.70 27.54 27.66 27.03 27.17 27.07 26.85 27.40 26.82 27.52 26.92 27.52 26.57 27.60 26.781924 27.04 26.82 27.39 26.94 27.65 27.19 27.75 27.62 27.02 27.67 27.02 27.61 26.25 27.16 26.09 26.80 25.89 26.78 26.28 26.88 25.56 26.53 25.93 26.731925 25.55 26.71 26.29 26.86 26.73 27.13 27.25 27.60 27.47 27.64 27.51 27.58 27.73 27.16 27.55 26.81 27.52 26.83 27.58 26.93 27.66 26.65 28.19 26.811926 28.10 26.75 28.06 26.94 28.44 27.25 28.78 27.71 28.69 27.72 28.29 27.62 27.86 27.22 27.03 26.85 26.68 26.86 26.34 26.95 26.38 26.78 26.36 26.901927 26.68 26.81 27.00 27.03 27.08 27.38 27.50 27.82 27.28 27.80 27.54 27.68 26.92 27.27 26.78 26.92 26.60 26.87 27.00 26.95 26.61 26.84 26.84 26.911928 27.05 26.83 26.97 27.06 27.01 27.43 27.55 27.89 27.83 27.80 27.43 27.68 27.25 27.26 26.59 26.91 26.62 26.82 26.61 26.86 26.49 26.75 26.56 26.811929 26.43 26.77 26.69 27.02 27.11 27.39 27.62 27.90 27.70 27.81 27.81 27.66 27.21 27.27 26.98 26.87 27.05 26.73 27.13 26.78 26.84 26.71 27.22 26.721930 26.93 26.73 27.15 26.95 27.55 27.34 28.18 27.89 27.83 27.82 27.95 27.66 27.86 27.24 27.56 26.87 28.04 26.75 27.87 26.76 28.44 26.72 28.00 26.661931 28.07 26.73 28.10 26.93 28.44 27.29 28.73 27.86 28.49 27.77 28.16 27.60 27.63 27.13 27.02 26.81 26.33 26.71 26.51 26.77 26.38 26.69 26.31 26.621932 26.16 26.67 26.57 26.89 27.51 27.25 28.02 27.85 28.14 27.73 27.87 27.55 27.11 27.10 26.97 26.78 26.77 26.73 26.75 26.79 26.61 26.72 26.18 26.661933 26.36 26.62 26.68 26.89 27.05 27.28 27.78 27.89 27.46 27.72 26.83 27.51 26.56 27.07 25.93 26.75 25.98 26.74 25.63 26.74 25.59 26.70 25.38 26.621934 25.64 26.56 25.89 26.85 26.31 27.26 27.35 27.90 27.37 27.70 27.35 27.47 26.80 27.03 26.55 26.72 26.23 26.74 26.48 26.67 26.54 26.68 26.34 26.551935 26.26 26.57 26.57 26.86 26.98 27.27 27.45 27.91 27.32 27.72 27.28 27.48 26.58 27.02 26.93 26.72 26.83 26.68 27.01 26.58 26.94 26.64 26.55 26.521936 27.32 26.61 27.25 26.91 27.26 27.32 28.06 27.95 27.80 27.77 27.33 27.52 26.88 27.02 26.55 26.76 26.65 26.67 27.12 26.60 26.62 26.65 27.22 26.601937 26.27 26.65 27.06 26.94 27.51 27.39 27.98 27.99 27.44 27.79 27.39 27.51 27.32 27.01 26.67 26.74 26.93 26.67 26.63 26.60 26.87 26.65 26.80 26.631938 26.37 26.65 26.99 26.92 27.20 27.29 27.86 27.97 27.53 27.77 26.80 27.51 26.24 27.02 26.07 26.74 26.47 26.64 25.98 26.56 25.93 26.61 25.79 26.631939 25.91 26.63 25.81 26.92 26.41 27.28 27.50 27.97 27.61 27.80 27.74 27.56 27.48 27.07 26.94 26.80 27.19 26.67 26.27 26.60 26.98 26.63 26.64 26.671940 27.76 26.65 28.14 26.96 28.44 27.29 28.57 27.97 28.21 27.84 28.24 27.57 27.43 27.10 27.63 26.77 26.80 26.64 27.06 26.54 27.35 26.58 27.98 26.641941 27.95 26.69 28.11 26.91 28.67 27.25 29.13 27.91 29.18 27.83 28.57 27.59 27.95 27.12 27.66 26.72 27.43 26.59 27.72 26.47 27.83 26.54 27.86 26.591942 27.19 26.57 27.29 26.85 27.51 27.23 28.34 27.86 27.76 27.81 27.17 27.63 26.67 27.12 25.92 26.70 25.58 26.52 25.41 26.41 25.15 26.48 25.35 26.561943 25.38 26.62 25.58 26.84 26.16 27.27 27.17 27.85 27.51 27.83 27.58 27.70 27.13 27.14 26.93 26.73 26.52 26.48 26.29 26.38 26.16 26.46 26.17 26.611944 26.15 26.64 26.92 26.90 27.05 27.32 27.88 27.88 28.00 27.87 27.72 27.71 27.30 27.15 26.88 26.75 26.44 26.43 26.51 26.37 26.31 26.39 26.33 26.611945 26.22 26.54 26.29 26.82 26.47 27.22 27.01 27.82 27.41 27.80 27.09 27.60 26.62 27.05 26.03 26.66 25.93 26.32 25.87 26.30 26.23 26.21 26.05 26.431946 26.14 26.30 26.53 26.57 26.90 27.00 27.29 27.66 27.47 27.65 27.83 27.48 27.26 26.99 26.36 26.60 26.56 26.26 26.73 26.23 26.47 26.08 26.61 26.281947 26.97 26.17 26.63 26.45 27.54 26.88 27.70 27.58 27.32 27.56 27.75 27.42 26.83 26.98 26.51 26.63 25.70 26.30 25.92 26.29 25.93 26.12 26.77 26.281948 26.63 26.23 27.13 26.51 27.89 26.93 28.02 27.64 28.17 27.58 27.75 27.44 27.16 26.99 26.85 26.66 26.73 26.39 26.06 26.38 26.35 26.22 26.96 26.351949 26.12 26.35 27.02 26.58 26.70 27.01 27.96 27.68 27.79 27.59 26.97 27.47 26.84 26.95 26.56 26.60 26.10 26.40 26.01 26.37 25.33 26.22 25.39 26.351950 25.53 26.38 25.26 26.57 26.18 27.02 26.86 27.65 26.56 27.51 26.82 27.35 26.14 26.86 26.24 26.54 25.65 26.34 25.90 26.30 25.27 26.11 25.55 26.27
25

Table 3. HadSST monthly and 10-yma values for the Niño 3.4 region from 1871 to April 2009 (Continued).

Year

January February March April May June July August September October November December

Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma

1951 25.45 26.32 26.02 26.52 26.48 26.99 27.60 27.63 27.77 27.47 27.60 27.27 27.88 26.78 27.77 26.53 27.42 26.28 27.52 26.23 27.44 25.99 27.30 26.191952 26.97 26.24 27.00 26.48 27.30 26.95 28.18 27.64 27.48 27.51 27.03 27.25 26.63 26.78 26.45 26.57 26.40 26.32 26.70 26.27 26.33 26.04 26.04 26.211953 26.94 26.26 27.00 26.52 27.48 26.96 28.54 27.66 28.21 27.56 28.10 27.28 27.42 26.84 26.91 26.64 27.42 26.38 26.84 26.38 26.96 26.15 26.74 26.261954 26.97 26.38 26.98 26.59 27.27 27.02 27.45 27.67 27.34 27.56 26.88 27.31 26.20 26.85 25.80 26.65 25.72 26.38 25.82 26.46 25.49 26.22 25.79 26.311955 25.92 26.48 25.98 26.66 26.46 27.11 26.82 27.72 26.64 27.63 26.49 27.37 25.91 26.90 25.96 26.68 25.42 26.44 25.14 26.54 24.75 26.33 25.07 26.421956 25.35 26.58 25.79 26.76 26.32 27.19 26.99 27.78 27.28 27.70 26.85 27.41 26.28 26.89 26.06 26.65 25.84 26.44 26.04 26.50 25.64 26.33 26.01 26.421957 26.02 26.60 26.52 26.78 27.34 27.20 28.19 27.76 28.31 27.71 28.22 27.44 27.91 26.86 27.66 26.61 27.28 26.37 27.48 26.41 27.74 26.28 27.76 26.381958 28.12 26.54 28.16 26.74 28.25 27.17 28.08 27.68 28.19 27.69 27.99 27.45 27.26 26.90 27.12 26.66 26.44 26.35 26.70 26.43 26.71 26.29 26.89 26.421959 27.01 26.52 27.26 26.73 27.52 27.15 28.04 27.63 27.85 27.66 27.36 27.43 26.95 26.95 26.47 26.72 26.22 26.36 26.84 26.46 26.48 26.32 26.54 26.451960 26.60 26.54 26.52 26.77 27.17 27.16 27.78 27.66 27.92 27.72 27.48 27.51 26.98 27.07 26.87 26.85 26.79 26.49 26.67 26.62 26.27 26.49 26.60 26.591961 26.43 26.66 26.80 26.88 27.16 27.27 27.90 27.77 27.86 27.82 27.79 27.64 26.90 27.23 26.62 26.99 26.23 26.67 26.02 26.81 26.46 26.70 26.30 26.751962 26.33 26.78 26.60 26.95 26.85 27.33 27.45 27.79 27.45 27.81 27.47 27.66 26.92 27.25 26.74 26.97 26.19 26.65 26.41 26.79 26.22 26.66 26.09 26.691963 26.26 26.68 26.50 26.85 27.20 27.22 27.71 27.70 27.86 27.74 27.81 27.62 27.95 27.23 27.78 26.92 27.40 26.62 27.57 26.75 27.40 26.62 27.63 26.641964 27.33 26.59 27.31 26.75 27.10 27.15 27.24 27.67 27.13 27.72 26.81 27.64 26.58 27.26 26.11 26.97 25.82 26.68 25.73 26.79 25.55 26.71 25.52 26.701965 26.01 26.64 26.41 26.80 26.92 27.18 27.68 27.68 28.05 27.74 28.14 27.67 28.03 27.24 28.12 26.97 28.01 26.69 28.34 26.79 28.20 26.73 28.04 26.681966 27.71 26.60 27.59 26.77 28.08 27.14 28.31 27.63 27.81 27.69 27.82 27.62 27.45 27.19 26.77 26.90 26.70 26.64 26.69 26.76 26.28 26.67 26.32 26.591967 26.02 26.52 26.20 26.70 26.79 27.09 27.24 27.60 27.63 27.69 27.56 27.62 27.12 27.23 26.57 26.95 26.17 26.72 26.35 26.86 26.32 26.76 26.24 26.701968 25.98 26.60 26.02 26.76 26.50 27.12 27.30 27.63 27.43 27.70 27.87 27.61 27.54 27.20 27.20 26.92 26.80 26.70 27.05 26.84 27.42 26.73 27.35 26.671969 27.48 26.56 27.79 26.73 27.86 27.09 28.10 27.61 28.25 27.67 27.95 27.57 27.32 27.10 27.39 26.84 27.22 26.63 27.39 26.74 27.40 26.60 27.27 26.521970 27.13 26.43 27.12 26.63 27.52 27.02 27.95 27.56 27.87 27.61 27.38 27.49 26.25 27.00 25.92 26.74 25.97 26.52 26.08 26.59 25.81 26.45 25.47 26.381971 25.11 26.29 25.48 26.53 25.96 26.93 26.80 27.49 27.04 27.52 26.91 27.40 26.59 26.89 26.22 26.64 26.00 26.42 25.95 26.49 25.80 26.37 25.69 26.271972 26.00 26.22 26.55 26.50 27.00 26.90 27.98 27.45 28.19 27.51 28.35 27.42 28.06 26.92 28.18 26.69 27.94 26.50 28.50 26.59 28.53 26.50 28.78 26.381973 28.18 26.35 27.84 26.61 27.83 26.98 27.70 27.47 27.30 27.52 26.83 27.41 26.08 26.91 25.66 26.67 25.35 26.52 25.15 26.62 24.58 26.52 24.41 26.421974 24.56 26.37 25.26 26.63 25.82 27.00 26.77 27.47 27.07 27.49 26.99 27.37 26.58 26.85 26.56 26.61 26.40 26.49 25.98 26.57 25.70 26.45 25.73 26.391975 26.21 26.33 26.43 26.58 26.66 26.96 27.18 27.46 26.87 27.48 26.43 27.39 25.99 26.89 25.72 26.63 25.31 26.52 25.26 26.58 25.19 26.48 24.95 26.461976 24.78 26.38 25.71 26.62 26.58 27.02 27.35 27.50 27.37 27.52 27.69 27.46 27.38 26.95 27.18 26.69 27.32 26.59 27.59 26.65 27.54 26.56 27.23 26.581977 27.42 26.46 27.31 26.67 27.65 27.10 27.52 27.54 27.84 27.57 28.05 27.50 27.67 26.95 27.13 26.69 27.19 26.63 27.62 26.70 27.69 26.60 27.67 26.641978 27.30 26.53 27.27 26.73 27.32 27.16 27.40 27.60 27.37 27.67 27.23 27.59 26.75 26.99 26.26 26.73 26.15 26.69 26.39 26.74 26.50 26.65 26.66 26.711979 26.63 26.63 26.86 26.83 27.38 27.27 27.94 27.68 27.77 27.76 27.72 27.65 27.02 27.05 27.09 26.78 27.23 26.73 27.05 26.76 27.00 26.69 27.28 26.731980 27.13 26.67 27.09 26.85 27.35 27.30 27.97 27.68 28.00 27.78 28.05 27.67 27.25 27.10 26.65 26.81 26.63 26.77 26.63 26.80 26.75 26.73 26.94 26.761981 26.12 26.69 26.31 26.85 27.24 27.29 27.60 27.66 27.76 27.78 27.54 27.69 26.79 27.13 26.70 26.84 26.68 26.82 26.70 26.84 26.39 26.79 26.65 26.841982 26.54 26.76 26.64 26.90 27.24 27.34 28.01 27.72 28.51 27.83 28.61 27.73 27.86 27.17 27.80 26.90 28.14 26.87 28.73 26.87 28.72 26.81 28.92 26.851983 29.01 26.77 28.98 26.92 28.95 27.39 28.89 27.77 28.99 27.85 28.31 27.72 27.11 27.16 26.75 26.92 26.26 26.89 25.70 26.81 25.52 26.72 25.64 26.751984 25.78 26.67 26.23 26.84 26.78 27.33 27.17 27.70 27.22 27.78 26.79 27.64 26.82 27.10 26.47 26.83 26.40 26.81 25.90 26.68 25.48 26.59 25.05 26.611985 25.69 26.55 25.85 26.77 26.30 27.26 26.79 27.64 26.97 27.76 26.93 27.59 26.62 27.09 26.38 26.81 26.18 26.78 26.09 26.66 26.22 26.56 26.19 26.561986 25.79 26.57 26.12 26.81 26.75 27.28 27.36 27.66 27.39 27.80 27.61 27.61 27.38 27.15 27.11 26.86 27.34 26.81 27.63 26.72 27.70 26.62 27.56 26.641987 27.77 26.70 27.94 26.93 28.50 27.36 28.66 27.74 28.77 27.85 28.92 27.63 28.56 27.18 28.36 26.84 28.28 26.75 28.10 26.65 27.94 26.58 27.64 26.601988 27.27 26.67 27.11 26.93 27.54 27.37 27.28 27.79 26.82 27.87 26.23 27.61 25.69 27.19 25.43 26.80 25.42 26.71 24.65 26.60 24.48 26.54 24.60 26.541989 24.63 26.61 25.39 26.86 25.93 27.33 26.66 27.81 27.06 27.90 27.04 27.67 26.76 27.24 26.29 26.86 26.37 26.78 26.33 26.75 26.36 26.73 26.46 26.741990 26.60 26.75 27.12 26.97 27.46 27.42 28.03 27.90 28.19 27.99 27.69 27.77 27.37 27.30 27.05 26.92 26.87 26.82 26.86 26.84 26.73 26.83 26.90 26.86
26Table 3. HadSST monthly and 10-yma values for the Niño 3.4 region from 1871 to April 2009 (Continued).

Year

January February March April May June July August September October November December

Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma Mon 10-yma

1991 27.09 26.86 27.08 27.06 27.36 27.50 27.98 27.97 28.30 28.04 28.34 27.81 27.84 27.31 27.30 26.89 26.98 26.77 27.64 26.77 27.79 26.74 28.20 26.771992 28.19 26.78 28.39 26.98 28.76 27.43 29.18 27.95 29.13 28.04 28.22 27.80 27.50 27.31 26.73 26.89 26.61 26.76 26.39 26.76 26.51 26.73 26.63 26.761993 26.86 26.79 27.18 27.00 27.73 27.43 28.68 27.99 28.79 28.12 28.33 27.85 27.55 27.37 27.04 26.94 27.01 26.81 27.09 26.85 26.94 26.84 26.77 26.851994 26.61 26.90 26.60 27.09 27.19 27.51 27.80 28.07 28.00 28.21 27.96 27.89 27.38 27.39 27.40 26.95 27.15 26.81 27.63 26.87 27.79 26.83 27.80 26.801995 27.68 26.83 27.64 26.99 27.75 27.46 28.04 28.04 27.89 28.15 27.77 27.84 27.26 27.33 26.50 26.91 26.18 26.76 26.01 26.80 25.87 26.73 25.86 26.671996 25.93 26.67 26.10 26.85 26.78 27.36 27.43 27.96 27.46 28.06 27.57 27.76 27.08 27.27 26.58 26.86 26.41 26.71 26.46 26.71 26.35 26.62 26.16 26.511997 26.15 26.51 26.53 26.72 27.19 27.26 28.11 27.87 28.74 27.97 28.84 27.73 28.83 27.25 28.81 26.87 28.85 26.74 29.02 26.72 29.08 26.63 28.89 26.471998 29.00 26.46 28.84 26.65 28.75 27.19 28.67 27.76 28.55 27.84 27.30 27.70 26.49 27.26 26.04 26.91 25.93 26.78 25.54 26.80 25.43 26.71 25.08 26.551999 25.05 26.50 25.35 26.67 26.34 27.19 26.96 27.71 26.99 27.77 26.74 27.65 26.39 27.26 25.89 26.91 25.91 26.79 25.70 26.80 25.24 26.69 25.04 26.532000 24.79 26.49 25.23 26.66 26.00 27.17 26.97 27.71 27.07 27.78 26.93 27.65 26.65 27.27 26.52 26.93 26.36 26.82 26.18 26.82 25.91 26.68 25.67 26.502001 25.70 26.44 26.13 26.63 26.78 27.15 27.47 27.72 27.57 27.81 27.58 27.67 27.24 27.28 26.80 26.98 26.47 26.90 26.47 26.90 26.37 26.76 26.13 26.582002 26.44 26.48 26.76 26.64 27.36 27.14 27.91 27.69 28.07 27.76 28.37 27.61 27.80 27.19 27.57 26.89 27.57 26.79 27.89 26.77 28.06 26.63 28.00 26.462003 27.56 26.32 27.40 26.47 27.74 27.00 27.74 27.58 27.34 27.63 27.50 27.54 27.37 27.13 26.92 26.81 26.90 26.66 27.19 26.63 27.05 26.47 26.91 26.292004 26.84 26.32 26.93 26.32 27.16 26.88 27.83 27.52 27.96 – 27.82 – 27.64 – 27.54 – 27.42 – 27.46 – 27.27 – 27.30 –2005 27.14 – 27.02 – 27.54 – 28.05 – 28.16 – 27.91 – 27.22 – 26.83 – 26.67 – 26.59 – 26.21 – 25.83 –2006 25.60 – 26.05 – 26.53 – 27.47 – 27.76 – 27.78 – 27.25 – 27.25 – 27.38 – 27.49 – 27.64 – 27.69 –2007 27.17 – 26.88 – 27.11 – 27.61 – 27.47 – 27.52 – 26.86 – 26.31 – 25.71 – 25.33 – 25.07 – 24.98 –2008 24.79 – 25.07 – 26.09 – 26.88 – 27.22 – 27.24 – 27.19 – 26.83 – 26.47 – 26.43 – 26.29 – 25.69 –2009 25.58 – 26.05 – 26.54 – 27.52 – – – – – – – – – – – – – – – – –

1871–2008 Statistics:

Mean 26.54 – 26.72 – 27.13 – 27.64 – 27.69 – 27.56 – 27.07 – 26.76 – 26.62 – 26.63 – 26.53 – 26.54 –

sd 0.95 – 0.83 – 0.70 – 0.58 – 0.57 – 0.55 – 0.60 – 0.66 – 0.72 – 0.84 – 0.95 – 0.97 –

High 29.01 – 29.19 – 28.95 – 29.18 – 29.18 – 28.92 – 28.83 – 28.81 – 28.85 – 29.02 – 29.08 – 29.07 –

Low 24.09 – 24.65 – 25.82 – 26.47 – 26.46 – 26.23 – 25.69 – 25.39 – 25.31 – 24.65 – 24.48 – 24.41 –

medium 26.365 – 26.655 – 27.155 – 27.61 – 27.685 – 27.54 – 27.08 – 26.72 – 26.58 – 26.51 – 26.385 – 26.40 –

CV 0.036 – 0.031 – 0.026 – 0.021 – 0.021 – 0.020 – 0.022 – 0.025 – 0.027 – 0.032 – 0.036 – 0.037 –

PCS 0.55 – 0.23 – –0.11 – 0.16 – 0.03 – 0.11 – –0.05 – 0.18 – 0.17 – 0.14 – 0.46 – 0.43 –

na 69 – 69 – 69 – 70 – 69 – 70 – 70 – 69 – 70 – 70 – 69 – 69 –nb 69 – 69 – 69 – 68 – 69 – 68 – 68 – 69 – 68 – 68 – 69 – 69 –

nra 29 – 34 – 29 – 30 – 33 – 29 – 30 – 33 – 32 – 33 – 34 – 32 –

z –2.04 – –0.34 – –2.04 – –1.70 – –0.68 – –2.04 – –1.70 – –0.68 – –1.02 – –0.68 – –0.34 – –1.02 –

random no – yes – no – no – yes – no – no – yes – yes – yes – yes – yes –

±50% 0.64 – 0.56 – 0.47 – 0.39 – 0.39 – 0.37 – 0.41 – 0.45 – 0.49 – 0.57 – 0.64 – 0.66 –
27

1870 1875 1880 1885

24.5

25.0

25.5

26.0

26.5

27.0

27.5

28.0

28.5

29.0

29.5

24.0

Calendar Date

HadSST

1890 1895 1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Figure 15. Monthly and 12-mma values of nonseasonally adjusted HadSST values 

from January 1871 to January 2010.

2.3 2-mma Values of Seasonally Adjusted Monthly Means of HadSST (D(m2)) 

and SOI (SOI(2)) in the Niño 3.4 Region (1871–2008)

Figure 16 depicts the 2-mma values of the seasonally adjusted monthly means of HadSST 

(D(m2)), where the shaded portions represent anomalous ENSO extreme events. The seasonally 

adjusted values were determined by subtracting the long-term monthly averages from the observed 

HadSST monthly values, then performing a 2-mma of the differences, with determination of anomalous HadSST ENSO extremes (based on D(m2) values) following that used in the determination of 

ONI anomalous ENSO extreme events (see section 1).

From figure 16, some 33 EN and 27 LN events are identified. For convenience, the listing of 

EN and LN events is given in table 4, identifying the start, peak, and end dates (by year-month); 

the duration of each event (in months); the event type (EN or LN); the strength of each event, both 

in terms of class strength (i.e., W, M, and S) and peak anomalous temperature in degrees Celsius; 

and comments, where SP means single peak, DP means double peak, and MP means multiple peaks 

(three or more).

1870 1875 1880 1885 1890 1895 1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

–2.0

–1.5

–1.0

–0.5

0.0

0.5

1.0

1.5

2.0

2.5

–2.5

Calendar Date

HadSST Anomaly

Figure 16. Monthly and 2-mma values of the seasonally adjusted values of HadSST 

anomaly (D(m2)) from February 1871 to January 2010, where shaded 

portions reflect occurrences of warm EN events (positive anomalies) 

and cold LN events (negative anomalies), respectively.
28

Table 4. Listing of EN and LN events based on the 

HadSST dataset from 1871 to 2008.

Start Peak End

Duration

(mo) Type

Strength

(degrees) Comment

1872-08 1873-02 1873-04 9 LN W(–0.97) SP

1873-10 1874-11 1875-01 16 LN M(–1.16) SP

1875-03 1876-02 1876-05 15 LN M(–1.06) MP

1877-02 1878-01 1878-06 17 EN VS(+2.48)* SP

1879-05 1879-12 1880-03 11 LN W(–0.98) SP

1886-05 1887-03/04 1887-06 14 LN M(–1.03) DP

1888-02 1888-11 1889-04 15 EN S(+1.98) DP

1889-08 1890-01 1890-12 17 LN VS(–2.04)* DP

1892-08 1892-11 1895-01 30 LN M(–1.39) MP

1896-07 1896-12 1897-03 9 EN S(+1.59) SP

1899-08 1899-12 1900-10 15 EN M(+1.49) DP

1902-05 1902-11 1903-04 12 EN S(+1.57) SP

1903-11 1903-12 1904-04 6 LN W(–0.82) SP

1904-10 1905-09 1906-04 19 EN M(+1.38) DP

1908-11 1908-12 1909-03 5 LN W(–0.81) SP

1909-06 1909-11 1911-05 24 LN M(–1.23) MP

1911-11 1912-01 1912-04 6 EN M(+1.27) SP

1913-11 1913-12 1914-04 6 EN W(+0.86) SP

1914-12 1915-06 1915-06 7 EN W(+0.84) DP

1916-07 1916-12 1917-03 9 LN S(–1.58) SP

1918-09 1919-01 1919-09 13 EN M(+1.48) DP

1923-09 1923-11 1924-02 6 EN W(+0.98) SP

1924-06 1924-12 1925-02 9 LN W(–0.80) DP

1925-07 1926-01 1926-07 13 EN S(+1.53) SP

1930-07 1930-11 1931-07 13 EN S(+1.63) SP

1933-06 1933-12 1934-03 10 LN M(–1.04) SP

1938-10 1939-02 1939-03 6 LN W(–0.79) SP

1940-01 1940-02 1940-08 8 EN M(+1.34) DP

1940-11 1941-04 1942-03 17 EN S(+1.50) DP

1942-07 1942-11 1943-04 10 LN M(–1.29) SP

1949-10 1950-02 1951-03 18 LN M(–1.22) MP

1951-07 1951-08 1951-12 6 EN W(+0.91) SP

1954-06 1955-11 1956-12 31 LN S(–1.56) MP

1957-05 1958-01 1958-04 12 EN M(+1.46) DP

1963-07 1963-12 1964-01 7 EN W(+0.96) DP

1964-05 1964-11 1965-01 9 LN W(–0.97) DP

1965-06 1965-11 1966-04 11 EN S(+1.64) SP

1968-11 1969-02 1969-04 6 EN W(+0.95) SP

1969-08 1969-11 1970-01 6 EN W(+0.81) SP

1970-07 1971-01 1972-01 19 LN M(–1.29) MP

1972-05 1972-11/12 1973-03 11 EN VS(+2.03)* SP

1973-06 1973-12 1974-06 13 LN VS(–2.05)* SP

1975-04 1975-12 1976-03 12 LN S(–1.57) SP

1976-09 1976-11 1977-02 6 EN W(+0.92) SP

1977-09 1977-11 1978-01 6 EN M(+1.11) SP

1982-05 1983-01 1983-06 14 EN VS(+2.40)* DP
29

Table 4. Listing of EN and LN events based on the 

HadSST dataset from 1871 to 2008 (Continued).

Start Peak End

Duration

(mo) Type

Strength

(degrees) Comment

1983-10 1983-11 1984-02 5 LN W(–0.96) SP

1984-10 1984-12 1985-06 9 LN M(–1.22) SP

1986-09 1987-09 1988-01 17 EN S(+1.60) DP

1988-05 1988-11 1989-06 14 LN VS(–2.01)* DP

1991-05 1992-01/02 1992-06 14 EN S(+1.66) DP

1993-03 1993-05 1993-07 5 EN M(+1.00) SP

1994-08 1994-12 1995-03 8 EN M(+1.23) SP

1995-10 1995-11/12 1996-02 5 LN W(–0.66) SP

1997-04 1997-11 1998-05 14 EN VS(+2.46)* SP

1998-07 2000-01 2000-06 24 LN S(–1.62) DP

2002-06 2002-11 2003-03 10 EN M(+1.45) SP

2004-07 2004-09/10 2005-01 7 EN W(+0.80) SP

2006-09 2006-11 2007-01 5 EN M(+1.06) SP

2007-08 2008-01 2008-05 10 LN S(–1.68) SP

Notes * VS = very strong events are those where the anomaly exceeds the ±2 degree 

 threshold.

SP = single peak.

DP = double peak.

MP = multiple peaks (three or more).

Of the 33 EN events, 9 are considered W, 11 are M, and 13 are S or very strong (VS) in 

strength. The greatest positive anomalies (EN events classified as VS) occurred in January 1877 

(+2.48 °C), November/December 1972 (+2.03 °C), January 1983 (+2.40 °C), and November 1997 

(+2.46 °C). The longest duration EN event was 19 months in length, occurring between October 

1904 and April 1906. The average duration (±1 sd) of EN events is 10.3±4.2 months. Twenty-one of 

33 EN events were single peaked, 12 were double peaked, and none had 3 or more peaks.

Of the 27 LN events, 9 are considered W, 10 are M, and 8 are S or VS. The greatest negative 

anomalies (LNs classified as VS) occurred in January 1890 (–2.04 °C), December 1973 (–2.05 °C), 

and November 1988 (–2.01 °C). The longest duration LN event was 31 months in length, occurring 

between June 1954 and December 1956. The average duration of LN events is 13.3±7.2 months. 

Fifteen of 27 LN events were single peaked, 6 were double peaked, and 6 had multiple peaks.

Table 5 shows the frequency of occurrence of EN and LN event starts, peaks, and ends for 

selected monthly intervals. Hence, half (30 of 60 events) of all EN and LN events have onset during 

the interval July to October, nearly all peak (52 of 60 events) during the interval November to February, and slightly more than half (36 of 60 events) end during the interval of March to June.
30

Table 5. Frequency of occurrence of start, peak, and end times 

for HadSST-determined EN and LN events.

Monthly Interval

EN(33) LN(27)

Start Peak End Start Peak End

November–February

March–June

July–October

8

9

16

26

3

4

9

18

6

2

11

14

26

1

0

9

18

0

Figure 17 displays the 2-mma values of the SOI (SOI(2)) for the interval 1871–present. Recall 

that extended intervals of positive SOI reflect LN-like conditions while extended intervals of negative SOI reflect EN-like conditions. Comparison of the 2-mma of SOI(2) (fig. 17) against D(m2) 

(fig.16) reveals a strong negative correlation between the two parameters, having r=–0.84, based on 

the interval 1971–2000 (the base period used in determination of the ONI), although, plainly, SOI(2) 

sometimes leads and sometimes lags D(m2). The overall negative correlation weakens if one uses the 

entire interval 1871–2008, suggesting, perhaps, that the early occurring values, in particular, of D(m2) 

(and hence, HadSST) might not be as reliable as compared to later occurring values. The strongest 

negative anomalies (usually associated with EN events) occurred in August 1882 (–21.8), May/June 

1896 (–31.0), April 1905 (–38.2), February 1983 (–31.3), May 1987 (–21.9), and March 1998 (–25.2). 

The strongest positive anomalies (usually associated with LN events) occurred in December 1872 

(27.9), August 1879 (21.5), December 1889 (22.0), April 1904 (20.5), August 1917 (31.9), June 1950 

(20.6), November 1973 (22.5), and August 1975 (21.3).

1870 1875 1880 1885

–40.0

–35.0

–30.0

–25.0

–20.0

–15.0

–10.0

–5.0

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

SOI (2)

1870 1875 1880 1885 1890 1895 1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965

Calendar Date

1970 1975 1980 1985 1990 1995 2000 2005

Figure 17. Presentation of 2-mma values of SOI (SOI(2)) anomaly from January 1871 

to January 2010.

Figures 18 and 19, respectively, depict the results of epoch analyses for the 33 EN and 27 

LN events catalogued in table 4 in terms of D(m2) (upper panels) and SOI(2) (lower panels) and 

strength, where 1 represents W events, 2 M events, and 3 S and VS events. As expected, S events are 

more likely to have a later-occurring peak and a longer duration than events of lesser strength (true 

using D(m2) or SOI(2)).
31

–6 0 6 12

–15.0

–10.0

–5.0

0

5.0

10.0

–0.5

0

0.5

1.0

1.5

2.0

2.5

–20.0

Elasped Time in Months From Event Start

–6 0 6 12

1 1

2

2

3

3

1

1

2

2

3

3

Elasped Time in Months From Event Start

D (m2) SOI (2)

 EN Events (33) Duration Rise

 1 W (9) 6.3 (0.5) 2.7 (1.6)

 2 M (11) 9.7 (4.6) 4.1 (3.0)

 3 S+VS (13) 13.6 (2.5) 7.1 (2.4)

All (33) 10.3 (4.2) 4.9 (3.0)

(a)

(b)

Figure 18. Results of epoch analysis for EN events, (a) D(m2) and (b) SOI(2).
32

–6 0 6 12

–5.0

0

5.0

10.0

15.0

20.0

–2.0

–1.5

–1.0

–0.5

0

0.5

1.0

–10.0

Elasped Time in Months From Event Start

–6 0 6 12

1

2

3

1

2

3

1

2

3

1

2

3

Elasped Time in Months From Event Start

D (m2) SOI (2)

LN Events (27) Duration Rise

 1 W (9) 7.2 (2.3) 3.7 (2.6)

 2 M (10) 16.5 (6.6) 6.0 (3.5)

 3 S+VS (8) 16.3 (7.6) 5.8 (1.0)

All (27) 13.3 (7.2) 5.1 (2.8)

(a)

(b)

Figure 19. Results of epoch analysis for LN events, (a) D(m2) and (b) SOI(2).
33

2.4 The ONI Values in the Niño 3.4 Region (1950–2008)

Figure 20 displays the ONI values for the interval 1950–present, plotted akin to that employed 

in figure 16 for D(m2). Again, the shaded portions of the figure denote the occurrences of the extremes 

of the ENSO cycle, where positive anomalies represent EN events and negative anomalies represent 

LN events. From figure 20, one can identify 31 extreme events, consisting of 18 EN and 13 LN events 

(since 1950). Recall from figure 16 that, for the same time interval (i.e., since January 1950), one can 

identify 30 extreme events using D(m2), as well, consisting of 18 EN events and 12 LN events, with 

the most recent 2009 EN event not included in figure 16. Hence, there appears generally good agreement in identifying the occurrences and strengths of the extremes using the two datasets. While true, 

some subtle differences are found. For example, in figure 16, the D(m2) LN event of 1973 began 

in June 1973 and ended in June 1974 with another separate LN event following in April 1975 that 

ended in March 1976. In figure 20, the ONI records the 1973 LN event as starting in May 1973 and 

being one long continuous event that ended in May 1976. Another difference is the inclusion of an 

LN event in 1983 in figure 16 but not included in figure 20, the inclusion of an EN event in 1993 in 

figure 16 but not included in figure 20, and the inclusion of a LN event in 2000 in figure 20 but not 

in figure 16. For the ONI-identified extremes, LN and EN events are found to average, respectively, 

about 15.0 and 10.1 months in duration, while for the same interval, the D(m2)-identified extremes 

of LN and EN events are found to average, respectively, about 13.7 and 9.2 months in duration. It 

appears then that extremes identified using the ONI values tend to be slightly longer in duration 

than when identified using D(m2). For convenience, table 6 is included, giving the event start, peak, 

and end times; duration; type; strength; and comments for the ONI-determined EN and LN events, 

constructed similar to that of table 4, which identified extremes using D(m2).

–3.0

–2.5

–2.0

–1.5

–1.0

–0.5

0

0.5

1.0

1.5

2.0

2.5

3.0

1950 1955 1960 1965

ONI

1970 1975 1980 1985

Calendar Date

1990 1995 2000 2005

ONI Anomaly

January 1950–January 2010

Figure 20. The ONI anomalies from January 1950 to January 2010, where shaded portions reflect

occurrences of warm EN events (positive anomalies) and cold LN events (negative 

anomalies), respectively.
34

Table 6. Listing of EN and LN events based on ONI (ERSST.v3b).

Start Peak End

Duration

(mo) Type

Strength

(degrees) Comments

B01-1950

08-1951

04-1954

04-1957

09-1962

07-1963

04-1964

06-1965

12-1967

11-1968

09-1969

07-1970

05-1972

05-1973

09-1976

09-1977

05-1982

10-1984

08-1986

05-1988

05-1991

05-1994

09-1995

05-1997

07-1998

10-2000

05-2002

06-2004

08-2006

09-2007

06-2009

01-1950(?)

10-1951

11-1955

01-1958

11-1962

11-1963

10-1964

11-1965

02-1968

01-1969

11-1969

01-1971

12-1972

12-1973

11-1976

11-1977

12-1982

12-1984

08-1987

11-1988

01-1992

12-1994

11-1995

11-1997

12-1999

12-2000

11-2002

09-2004

11-2006

01-2008

12-2009

03-1951

12-1951

01-1957

06-1958

01-1963

01-1964

01-1965

04-1966

04-1968

06-1969

01-1970

01-1972

03-1973

05-1976

02-1977

01-1978

06-1983

09-1985

02-1988

05-1989

07-1992

03-1995

03-1996

05-1998

06-2000

02-2001

03-2003

02-2005

01-2007

05-2008

–

>15(?)

5

34

15

5

7

10

11

5

8

5

19

11

37

6

5

14

12

19

13

15

11

7

13

24

5

11

9

6

9

>8

LN

EN

LN

EN

LN

EN

LN

EN

LN

EN

EN

LN

EN

LN

EN

EN

EN

LN

EN

LN

EN

EN

LN

EN

LN

LN

EN

EN

EN

LN

EN

S(–1.7)?

W(+0.8)

S(–2.0)

S(+1.7)

W(–0.7)

M(+1.0)

M(–1.2)

S(+1.6)

W(–0.9)

M(+1.0)

W(+0.8)

M(–1.3)

S(+2.1)

S(–2.1)

W(+0.8)

W(+0.7)

S(+2.3)

M(–1.1)

S(+1.6)

S(–1.9)

S(+1.8)

M(+1.3)

W(–0.7)

S(+2.5)

S(–1.6)

W(–0.7)

S(+1.5)

W(+0.5)

M(+1.1)

M(–1.4)

S(+1.8)

MP

SP

MP

SP

SP

SP

SP

SP

SP

SP

SP

MP

SP

MP

SP

SP

SP

SP

DP 

DP

DP

SP

SP

SP

DP

SP

SP

SP

SP

SP

SP(?)

Averages: EN

LN

 10.1#

15.0@

Notes: B means before.

? means uncertain.

# means excluding the 2009 EN event.

@ means excluding the 1950 LN event.

Correlation analysis of ONI and D(m2) during the ONI base period of 1971–2000 shows that 

the two parameters are highly correlated, having r = 0.99. The inferred regression equation between 

ONI and D(m2) using ONI as the independent variable is D(m2)=–0.047+0.991ONI (se=0.130 °C) 

and the inferred regression equation between ONI and D(m2) using D(m2) as the independent variable is ONI=0.048+0.989D(m2) (se=0.130 °C).

2.5. The Duration-Maximum Anomaly Association for ENSO Exteme Events

Figure 21 shows the scatter plots of (a) the duration of EN and LN events against their 

maximum anomalous excursion temperature using ONI (max ONI) for the interval 1950–2008 and 

(b) the duration of EN and LN events against their maximum anomalous excursion temperatures 
35

using D(m2) (max D(m2)) for the interval 1871–2008. In both panels, the larger filled circles represent two events, both having the same duration and maximum anomaly excursion temperature. In 

figure 21, one finds the association between the duration of an ENSO extreme event (i.e., EN and 

LN events) and the maximum anomalous excursion to be statistically important. Hence, knowing 

the maximum value of the anomaly, one can estimate the duration of the event (at least its minimum 

length). For example, an EN event having max ONI ≥1.3 °C has always had a duration ≥ 11 months; 

whereas, an EN event having max ONI<1.3 °C has always had a duration <11 months. The 2009 EN 

event, having had a max ONI=1.8 °C, therefore is not expected to end until May 2010 or later, based 

on the inferred preferential association. Based on D(m2), an EN event having max D(m2) ≥1.45 °C 

has always had a duration ≥ 9 months; whereas, an EN event having max D(m2)<1.45 °C almost 

always has had duration <9 months. For a LN event having max ONI (max D(m2)) equal to 

–1.25 °C (–1.23 °C) or cooler, one expects a duration of 13 months (11 months) or longer; whereas, 

for a LN event having max ONI (max D(m2)) equal to –1.2 °C (–1.22 °C) or warmer, one expects 

a duration of 12 months (10 months) or shorter.

It is apparent from figure 21 that LN events tend to be longer in duration than EN events, 

sometimes extending about 3 years in duration. El Niño events appear to have never extended longer 

than about a year-and-a-half in duration.

2.6. Recurrence Periods of the ENSO Extremes

Figure 22 depicts (a) RP against duration for the EN events (1950–2008) using D(m2), (b) 

RP against duration for the LN events (1950–2008) using D(m2), (c) RP against duration for the EN 

events (1950–2009) using ONI, and (d) RP against duration for the LN events (1950–2009) using 

ONI. For each panel, the thin vertical and horizontal lines represent the medians of the parameters, 

and the symbols refer to S or VS events (filled triangles), M events (filled squares), and W events 

(filled circles). Also, for each panel, the Fisher’s exact test for 2×2 contingency tables is applied. Figure 21c shows that there is a statistically significant association between RP and the duration for EN 

events during the interval 1950–2009 when based on ONI, one having P=1.3%, meaning that the 

probability of obtaining the observed distribution, or one more suggestive of a departure from independence, is computed to be P=1.3%. Using D(m2) (fig. 21a), however, one computes P=23.8%, 

inferring a statistically unimportant association. For LN events (figs. 21b and c), neither descriptor 

appears to be statistically important.

Figure 23 plots RP against duration for (a) EN and (b) LN events for the expanded interval 

1871–2008 using D(m2). For EN events, the distribution of RP against duration now has P=0.1%, 

inferring a highly statistically important association. Also, for EN events, linear regression analysis 

suggests that RP is highly statistically related to duration, having r=0.68 (se=25.1 months). Thus, as 

duration for an EN event increases, there is a strong tendency for the RP to increase such that those 

EN events having duration of 11 months or more usually have an RP≥39 months (true for 13 of 16 

EN events), and those having durations 10 months or less usually have an RP<39 months (true for 

13 of 16 EN events). For LN events, P=50.0%, inferring that the distribution results from chance. 

(In figure 22a, the large filled triangle at duration equal to 13 months and RP equal to 60 months is 

really two EN events, one of S and one of M strength.)
36

–2.5 –2.0 –1.5 –1.0 –0.5 0 0.5 1.0 1.5 2.0 2.5

5

0

10

15

20

25

30

35

Max D(m2)

5

3 10

9 ⇒ P = 3.8% 16

16 0

1 ⇒ P = 1.5×10–6% 

–2.5 –2.0 –1.5 –1.0 –0.5 0 0.5 1.0 1.5 2.0 2.5

(a)

(b)

5

0

10

15

20

25

30

35

40

Max ONI

Duration Duration

0

1 6

5 ⇒ P = 0.8% 9

8 0

0 ⇒ P = 4.1×10–3% 

Figure 21. Duration against (a) max ONI for LN and EN events (1950 – 2008) 

and (b) max D(m2) for LN and EN events (1871– 2008).
37

0 5 10 15 20 25 30 35

(b)

50

25

0

100

75

125

130

(a) (c)

50

25

0

75

50

25

0

75

Duration

Duration Duration

RP (D(m2))

⇒ P = 39.2% 

0 5 10 15 20 0 5 10 15 20

RP(D(m2))

RP(ONI) RP(ONI)

6

5 3

3 8

6 1

2

4

3 2

2 4

3 2

2

⇒ P = 23.8% ⇒ P = 1.3% 

0 5 10 15 20 25 30 35

(d)

50

25

0

100

75

125

130

Duration

⇒ P = 39.2% 

Figure 22. RP-duration distributions for (a) EN events (1950–2008) based on D(m2), 

(b) LN events (1950–2008) based on D(m2), (c) EN events (2000–2009) 

based on ONI, and (d) LN events (2000–2009) based on ONI.

0 5 10 15 20

(a) (b)

y

125

100

75

50

25

0

Duration

RP(D(m2))

 y = –8.741 + 5.46x

 r = 0.68, r2 = 0.463

 se = 25.053, cl >99.9%

13

13 3

3 ⇒ P = 0.1% 

0 5 10 15 20 25 30 35

125

100

75

50

25

0

Duration

RP(D(m2))

6

6 7

7 ⇒ P = 50% 

Figure 23. RP-duration distribution for (a) EN events (1871–2008) based on D(m2) 

and (b) LN events (1871–2008) based on D(m2).
38

2.7 Decadal Aspects of ENSO Extremes

Figure 24 displays (a) the number of EN onsets (NENO), (b) the number of EN months 

(NENM), (c) the number of LN onsets (NLNO), and (d) the number of LN months (NLNM) per 

decade (i.e., 1870–1879, 1880–1889, etc.) based on D(m2). For EN events, there has always been at 

least one EN onset occurring per decade, with two EN onsets per decade occurring about half of 

the time. The most number of EN onsets per decade has been four during the decades of 1900–1909, 

1960–1969, 1990–1999, and 2000–2009. For LN events, there has always been at least one LN onset 

occurring per decade, which also is the most frequently observed rate, having occurred about half of 

the time. Decades of three or more LN onsets per decade include 1870–1879, 1900–1909, 1970–1979, 

and 1980–1989. During the last decade, only one LN event had an onset, the LN event of August 

2007 (10-month duration).

For EN events, the NENM has been strikingly upwards since the decade of 1920–1929, as 

evinced by the inferred regression line. Presuming the validity of the inferred regression, extrapolation to the present decade (2010–2019), one projects NENM to be equal to about 37±3 months 

(using the midpoint of the decade, 2014.5 in the regression), which suggests that one should expect 

about 3–4 EN onsets during the present decade. Based on the 2×2 contingency table, while there 

appears to be a loose association between NENM and decadal time, the probability of obtaining 

the observed distribution, or one more suggestive of independence, is P=14.3%, indicating that the 

overall behavior possibly could be due to chance. The two largest NENM (41 months) occurred during the decades of 1900–1909 and 1990–1999.

For LN events, a strikingly downward progression is inferred for NLNM between the decades 

of 1870–1879 and 1940–1949. Since the decade of 1940–1949, however, NLNM has shown no distinctive pattern, sometimes being above and sometimes being below the median (22.5 months). The 

highest NLNM values occurred in the decades of 1870–1879 (48 months), 1950–1959 (46 months), 

and 1970–1979 (44 months). For the past decade (2000–2009), there were only 10 LN months, as 

previously noted (the August 2007 LN event).
39

1900

–09

(b) (d)

1950

–59

2000

–09

4

4 3

3

y

y

10

0

20

30

40

10

0

20

30

40

50 50

Decades

1900

–09

1950

–59

2000

–09

Decades

NENM

NLNM NLNO

 y = –439.5+0.237x

 r = 0.780, r2 = 0.609

se = 3.1, cl >99.9%

⇒ P = 50.0% 

5

5 2

2 ⇒ P = 14.3% 

 y = 856.2 – 0.436x

 r = –0.768, r2 = 0.589

 se = 10.6, cl >95%

1900

–09

(a) (c)

1950

–59

2000

–09

6

4

2

6

4

2

0 0

Decades

EN Events LN Events

1900

–09

1950

–59

2000

–09

Decades

NENO

Figure 24. Decadal variation of (a) NENO, (b) NENM, (c) NLNO, and (d) NLNM based 

on D(m2). The 2009 EN event observed in ONI has been included with the

2000–2009 decade, even though HadSST values have not yet been published.
40

3. SUMMARY

This study has examined the HadSST dataset for the Niño 3.4 region for the interval 1871–

present,26,27 investigating the onsets, strengths, and durations of EN and LN events. Also, comparison was made against both SOI values for the same time interval and the ONI-determined listing 

of ENSO extremes since 1950 to see what differences might possibly exist, if any, especially with 

regard to the identification of the occurrence, strength, and duration of ENSO extremes. Additionally, the duration-maximum anomaly excursion temperature association for ENSO extremes and the 

RP-duration association, previously found for EN events using ONI, were investigated to determine 

if they also might exist using the HadSST dataset, and the decadal aspects of the ENSO extremes 

were examined, anticipating what possibly might lie ahead for the current decade (2010–2019). 

Finally, table 7 is included in the Appendix, providing the monthly values of HadSST, 2-mma values 

of HadSST, 12-mma values of HadSST, the monthly differences between HadSST and the monthly 

adjusted average for 1871–2008 (D(m)), 2-mma values of D(m) (D(m2)), ONI, SOI, SOI(2), and 

comments. The comments column notes the occurrences of ENSO extremes based on D(m2), giving 

their start, peak, and end dates, as well as the strength of the individual peaks within each ENSO 

extreme event. For 1950–present, the occurrences of ENSO extremes are also shown based on ONI, 

marking their occurrences of start, peak, and end dates for comparison with D(m2). The monthly 

adjusted averages of HadSST appear at the bottom of table 7.

This investigation has shown that the annual mean HadSST temperature for the Niño 3.4 

region has averaged 26.95  °C between January 1871 and April 2009, with annual means varying 

nonrandomly, indicating the presence of a strong decadal signal imbedded within the dataset. Additionally, inferred was a possible rise over time of the annual mean SST temperature, but one of only 

marginal statistical importance (which disappears if one ignores the earliest portion of the data, prior 

to about 1895). Similar features are apparent in the annual highs, lows, and differences (i.e., high 

minus low values). Twelve-month moving averages of the nonseasonally adjusted monthly means of 

HadSST reveal strong episodic behavior, consisting of long intervals of warmer and cooler SST relative to the long-term mean. These episodes suggest the occurrences of long-term anomalous warming and cooling events. Instead, on the basis of 2-mma values of the seasonally adjusted monthly 

means of HadSST (D(m2)), one determines the occurrences of short-term episodes of warming and 

cooling, which are identified as EN and LN events, respectively (intervals of time when the anomalous monthly temperatures exceed specific thresholds continuously for a length of time longer than 

a specific minimum length).

For the interval February 1871–March 2009, the HadSST dataset is found to contain some 

60 ENSO extreme events, consisting of 33 EN and 27 LN events. The duration of an ENSO extreme 

event is found to be associated with the strength of the event such that stronger events (those having 

larger anomalous temperature excursions) tend to persist longer than weaker events.
41

A comparison of D(m2) against SOI(2) and ONI during the ONI base period (1971–2000) 

reveals strong statistical correlation between D(m2) and both SOI(2) and, especially, ONI. The 

inferred correlation between D(m2) and SOI(2) has r=–0.84, meaning that the two descriptors of 

ENSO extreme events behave oppositely, warmer anomalous temperatures being associated with 

negative anomalous pressure differences, and cooler anomalous temperatures being associated with 

positive anomalous pressure differences. The inferred correlation between D(m2) and ONI is even 

stronger, having r=0.99.

Comparison of the identification of EN and LN events using both the D(m2)- and ONIdetermined listings for the interval 1950–2008 reveals subtle differences. For example, the very strong 

June 1973 LN (duration 13 months) and strong April 1975 LN (duration 12 months) events are 

identified as one long continuous strong LN event (with multiple peaks) in the ONI listing instead of 

two separate events. Other differences include the inclusion of a weak LN event of 5-months duration and a moderate EN event of 5-months duration in the D(m2) listing but neither appearing in 

the ONI listing of events, and the inclusion of a weak LN event of 5-months duration in the ONI 

listing but not appearing in the D(m2) listing of events. For the interval 1950–2008, ONI-determined 

extremes tend to be slightly longer in duration (about 1 month) than measured using D(m2).

For both D(m2)- and ONI-determined extremes, strong associations are inferred to exist 

between the duration of the events and their maximum anomalous excursion temperatures. Hence, 

based on D(m2), when max D(m2) was 1.38 °C or warmer, the duration of the EN event was 10 

months or longer (10–19 months, true for 17 of 17 EN events), and, when max D(m2) was –1.22 °C 

or cooler, the duration of the LN event was 9 months or longer (9–31 months, true for 12 of 12 LN 

events). Similar results are found for ENSO extreme events based on ONI.

For both D(m2)- and ONI-determined ENSO extremes, a very strong association is inferred 

to exist between the occurrence of the next EN event and the duration of the last known EN event. 

For the interval 1950–2009, ONI-determined EN events tend to recur within 36 months when the 

duration of the last known EN event is less than 9 months, true for 6 of 8 EN events, while when 

the duration of the last known EN event is 10 months or longer, the recurrence rate tends to be 36 

months or longer, true for 8 of 9 EN events. For the interval 1871–2008, D(m2)-determined EN 

events tend to recur within 37 months when the duration of the last known EN event is 10 months or 

less, true for 13 of 16 EN events, while when the duration of the last known EN event is 11 months 

or longer, the recurrence rate tends to be 41 months or longer, true for 13 of 16 EN events. Because 

the S 2009 EN event (recorded in the ONI-listing but not yet appearing in the HadSST dataset) has 

already persisted for 8 months (thru January 2010) and S EN events tend to persist 11–19 months 

(based on ONI, the shortest D(m2)-determined S EN persisted only 9 months, with 12 of 13 S EN 

events persisting 11–17 months), one should not expect another EN event to recur until June 2012 

or later. (No such preferential association is found for LN events, either in the D(m2)- or ONI-determined listings.)

Finally, this study has shown that, since about the decade 1920–1929 the NENM have 

increased over time (in a saw-tooth pattern) . Extrapolating the fit to the present decade (2010–2019), 

presuming the pattern to continue, one expects NENM=37±3 months, probably ≥ 37 months (from 

the inferred saw-tooth pattern). This seems to indicate that one should expect about 3–4 EN events 
42

during the present decade. For NLNM, the indication is that it decreased over time between the 

decades 1870–1879 and 1940–1949, but no preferential rise has since been seen. Instead, after two 

large increases during the decades 1950–1959 and 1970-1979, NLNM has steadily declined again 

from 44 months in the decade 1970–1979 to only 10 months in the last decade (2000–2009). It is 

unclear what the present decade will experience with regards to LN events. The median value for 

NLNM is 22.5 months per decade.

In conclusion, the D(m2) index, based on seasonally adjusted monthly HadSST values, can 

be used to describe ENSO conditions and identify ENSO extreme events. This study also confirms 

the existence of preferential behavior between the recurrence rate of EN events and the duration of 

the last known EN event, as well as, between the duration of an ENSO extreme event (both EN and 

LN events) and its maximum anomalous excursion temperature.
43

APPENDIX

Table 7 is included to provide monthly values of HadSST, 2-mma values of HadSST, 12-mma 

values of HadSST, the monthly differences between HadSST and the monthly adjusted average for 

1871–2008 (D(m)), 2-mma values of D(m) (D(m2)), ONI, SOI, SOI(2), and comments. The comments column notes the occurrences of ENSO extremes based on D(m2), giving their start, peak, 

and end dates, as well as, the strength of the individual peaks. For 1950–present, the occurrences of 

ENSO extremes are also shown for ONI, marking the occurrences of the start, peak, and end dates, 

for comparison with D(m2). The monthly-adjusted averages of HadSST appear at the bottom of 

table 7.
44

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present.

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1871 01 26.33 – – –0.21 – – –11.3 –9.2

02 26.18 26.38 – –0.54 –0.40 – –1.3 –8.5

03 26.83 26.78 – –0.30 –0.38 – –20.0 –11.5

04 27.27 27.13 – –0.37 –0.39 – –4.6 –8.5

05 27.16 27.19 – –0.53 –0.46 – –4.7 –2.9

06 27.16 27.03 – –0.40 –0.45 – 2.4 0.8

07 26.62 26.74 26.59 –0.45 –0.38 – 3.1 3.1

08 26.54 26.55 26.57 –0.22 –0.25 – 3.8 4.1

09 26.51 26.49 26.57 –0.11 –0.17 – 5.8 3.5

10 26.40 26.42 26.55 –0.23 –0.19 – –1.4 0.7

11 26.35 26.28 26.55 –0.18 –0.28 – –0.2 2.0

12 26.01 26.06 26.55 –0.53 –0.48 – 9.7 11.5

1872 01 25.86 25.97 26.56 –0.68 –0.62 – 26.9 18.7

02 26.14 26.23 26.55 –0.58 –0.55 – 11.2 16.6

03 26.76 26.67 26.50 –0.37 –0.49 – 16.9 9.9

04 27.00 27.00 26.44 –0.64 –0.52 – –5.4 4.9

05 27.25 27.17 26.39 –0.44 –0.48 – 13.5 11.5

06 27.16 27.12 26.36 –0.40 –0.35 – 24.5 21.4

07 26.91 26.75 26.35 –0.16 –0.37 – 23.0 20.1

08 26.02 26.17 26.33 –0.74 –0.63 – 9.9 18.6 LN start

09 25.73 25.82 26.28 –0.89 –0.84 – 31.4 22.7 LN

10 25.79 25.79 26.25 –0.84 –0.81 – 19.0 25.1 LN

11 25.86 25.81 26.26 –0.67 –0.75 – 30.9 27.2 LN

12 25.71 25.77 26.26 –0.83 –0.77 – 28.0 27.9 LN

1873 01 25.79 25.76 26.25 –0.75 –0.83 – 24.7 22.2 LN

02 25.75 25.81 26.26 –0.97 –0.97 – 11.2 15.9 LN peak (W)

03 25.95 26.19 26.31 –1.18 –0.97 – 16.3 16.7 LN

04 27.10 26.87 26.34 –0.54 –0.66 – 22.9 18.5 LN end

05 27.33 27.24 26.35 –0.36 –0.40 – 11.9 4.0

06 27.21 27.10 26.36 –0.35 –0.37 – –30.9 –15.3

07 26.65 26.75 26.36 –0.42 –0.37 – –11.4 –14.9

08 26.48 26.51 26.35 –0.28 –0.30 – –5.9 –11.1

09 26.41 26.32 26.35 –0.21 –0.34 – –21.3 –16.6

10 25.96 26.05 26.33 –0.67 –0.55 – –17.8 –15.1 LN start

11 25.88 25.90 26.31 –0.65 –0.66 – –3.6 –2.9 LN

12 25.89 25.83 26.28 –0.65 –0.71 – 13.3 8.0 LN

1874 01 25.64 25.72 26.25 –0.90 –0.87 – 9.0 7.1 LN

02 25.70 25.72 26.21 –1.02 –1.06 – –2.8 –0.5 LN

03 25.85 26.06 26.15 –1.28 –1.10 – –5.2 –0.9 LN peak 1 (M)

04 26.83 26.63 26.09 –0.81 –0.90 – 9.8 6.8 LN

05 27.00 26.95 26.05 –0.69 –0.70 – 12.9 4.1 LN

06 26.96 26.79 26.01 –0.60 –0.69 – –19.2 –6.7 LN

07 26.22 26.31 26.00 –0.85 –0.81 – –1.4 –3.6 LN

08 25.82 25.87 26.04 –0.94 –0.93 – 7.5 8.5 LN

09 25.62 25.64 26.10 –1.00 –1.02 – 20.3 17.5 LN

10 25.49 25.48 26.14 –1.14 –1.12 – 21.9 17.4 LN

11 25.33 25.40 26.13 –1.20 –1.16 – 5.3 11.3 LN peak 2 (M)

12 25.45 25.53 26.12 –1.09 –1.01 – 12.8 9.4 LN
45

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1875 01 25.87 25.90 26.13 –0.67 –0.69 – 6.5 6.2 LN end

02 26.39 26.33 26.14 –0.33 –0.45 – –1.1 –1.4

03 26.66 26.65 26.16 –0.47 –0.50 – –10.0 –1.8 LN start

04 26.90 26.81 26.19 –0.74 –0.72 – 14.0 6.4 LN

05 26.77 26.84 26.23 –0.92 –0.81 – 7.5 13.7 LN peak 1 (W)

06 26.92 26.75 26.28 –0.64 –0.73 – 25.7 13.5 LN

07 26.37 26.43 26.28 –0.70 –0.69 – –4.9 3.5 LN

08 26.06 26.08 26.24 –0.70 –0.72 – –2.1 –0.2 LN

09 25.84 25.91 26.18 –0.78 –0.75 – 8.3 6.0 LN peak 2 (W)

10 25.90 25.91 26.15 –0.73 –0.69 – 9.3 2.9 LN

11 26.01 25.94 26.13 –0.52 –0.62 – –15.4 –6.7 LN

12 25.83 25.83 26.15 –0.71 –0.71 – –5.4 –3.7 LN

1876 01 25.63 25.66 26.18 –0.91 –0.92 – 11.3 7.1 LN

02 25.56 25.72 26.23 –1.16 –1.06 – 11.0 8.4 LN peak 3 (M)

03 26.13 26.10 26.30 –1.00 –1.05 – 0.2 5.2 LN

04 26.59 26.52 26.37 –1.05 –1.00 – 9.4 6.5 LN

05 26.78 26.85 26.45 –0.91 –0.80 – 6.8 10.1 LN end

06 27.25 27.04 26.52 –0.31 –0.43 – 17.2 8.9

07 26.88 26.93 26.61 –0.19 –0.19 – –5.6 4.6

08 26.71 26.76 26.74 –0.05 –0.05 – 12.3 7.4

09 26.73 26.76 26.88 0.11 0.10 – 10.5 6.3

10 26.85 26.81 27.01 0.22 0.21 – –8.0 –2.1

11 26.80 26.82 27.16 0.27 0.26 – –2.7 –4.1

12 26.81 26.84 27.30 0.27 0.30 – –3.0 –4.6

1877 01 26.93 26.97 27.43 0.39 0.39 – –9.7 –7.2

02 27.22 27.29 27.57 0.50 0.51 – –6.5 –6.9 EN start

03 27.78 27.76 27.72 0.65 0.61 – –4.7 –6.4 EN

04 28.27 28.24 27.87 0.63 0.71 – –9.6 –5.1 EN

05 28.62 28.55 28.03 0.93 0.90 – 3.6 –4.8 EN

06 28.67 28.65 28.20 1.11 1.18 – –16.8 –10.1 EN

07 28.64 28.59 28.38 1.57 1.48 – –10.2 –11.4 EN

08 28.42 28.50 28.55 1.66 1.69 – –8.2 –11.0 EN

09 28.50 28.53 28.66 1.88 1.87 – –17.2 –14.7 EN

10 28.68 28.65 28.71 2.05 2.05 – –16.0 –15.5 EN

11 28.74 28.81 28.73 2.21 2.25 – –12.6 –13.5 EN

12 29.07 28.97 28.74 2.53 2.43 – –12.6 –11.6 EN

1878 01 28.99 29.06 28.68 2.45 2.48 – –8.7 –12.8 EN peak (VS)

02 29.19 28.99 28.57 2.47 2.21 – –21.1 –16.6 EN

03 28.57 28.76 28.41 1.44 1.60 – –15.5 –15.2 EN

04 28.69 28.66 28.22 1.05 1.14 – –8.8 –7.8 EN

05 28.69 28.67 28.00 1.00 1.03 – 2.1 –1.9 EN

06 28.61 28.35 27.75 1.05 0.88 – –3.1 3.0 EN end

07 27.48 27.58 27.49 0.41 0.47 – 15.9 10.4

08 26.76 26.86 27.26 0.00 0.06 – 13.0 14.9

09 26.43 26.46 27.09 –0.19 –0.20 – 17.7 14.8

10 26.20 26.20 26.97 –0.43 –0.41 – 10.9 13.7

11 25.95 25.98 26.85 –0.58 –0.55 – 15.1 14.8

12 25.83 25.91 26.71 –0.71 –0.63 – 17.9 15.9
46

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1879 01 26.03 26.12 26.60 –0.51 –0.47 – 12.7 14.4

02 26.58 26.55 26.54 –0.14 –0.23 – 14.3 13.6

03 27.02 27.01 26.49 –0.11 –0.15 – 13.2 13.4

04 27.40 27.21 26.45 –0.24 –0.31 – 12.7 10.2

05 27.03 27.12 26.42 –0.66 –0.53 – 2.1 8.3 LN start

06 27.02 26.88 26.39 –0.54 –0.59 – 16.4 14.2 LN

07 26.46 26.53 26.36 –0.61 –0.59 – 21.8 20.7 LN

08 26.18 26.19 26.32 –0.58 –0.62 – 22.6 21.5 LN

09 25.93 25.96 26.28 –0.69 –0.70 – 18.9 18.9 LN

10 25.80 25.76 26.25 –0.83 –0.84 – 15.2 14.8 LN

11 25.52 25.60 26.25 –1.01 –0.96 – 9.8 7.3 LN

12 25.56 25.56 26.26 –0.98 –0.98 – –5.5 2.4 LN peak (W)

1880 01 25.58 25.69 26.27 –0.96 –0.90 – 10.8 6.0 LN

02 26.03 26.07 26.30 –0.69 –0.71 – 7.7 10.1 LN

03 26.63 26.62 26.35 –0.50 –0.53 – 14.3 10.4 LN end

04 27.20 27.05 26.43 –0.44 –0.48 – 5.3 9.3

05 27.15 27.17 26.53 –0.54 –0.50 – 12.3 9.8

06 27.08 27.00 26.64 –0.48 –0.47 – 9.1 8.0

07 26.70 26.78 26.74 –0.37 –0.34 – 1.6 6.7

08 26.63 26.67 26.84 –0.13 –0.13 – 14.3 9.6

09 26.72 26.74 26.92 0.10 0.09 – 8.1 8.8

10 26.90 26.86 27.00 0.27 0.25 – 4.8 6.2

11 26.90 26.87 27.08 0.37 0.31 – 7.2 4.3

12 26.77 26.83 27.15 0.23 0.29 – –1.9 –1.0

1881 01 26.87 26.88 27.19 0.33 0.29 – –7.3 –5.5

02 26.99 27.11 27.21 0.27 0.33 – –5.5 –4.1

03 27.58 27.58 27.20 0.45 0.43 – 1.8 –0.4

04 28.18 27.99 27.16 0.54 0.47 – 0.3 –0.5

05 28.03 28.04 27.10 0.34 0.40 – –4.3 –3.3

06 27.92 27.71 27.04 0.36 0.24 – –4.7 –4.8

07 26.96 27.14 26.99 –0.11 0.02 – –5.6 –6.8

08 26.71 26.70 26.93 –0.05 –0.10 – –11.4 –10.5

09 26.42 26.47 26.86 –0.20 –0.19 – –13.6 –15.6

10 26.31 26.28 26.81 –0.32 –0.33 – –23.9 –13.6

11 26.06 26.16 26.79 –0.47 –0.40 – 7.2 0.1

12 26.22 26.16 26.76 –0.32 –0.38 – 9.8 5.0

1882 01 26.13 26.17 26.72 –0.41 –0.41 – –6.8 –1.3

02 26.21 26.32 26.70 –0.51 –0.46 – –1.3 –1.1

03 26.73 26.89 26.69 –0.40 –0.27 – 5.1 2.5

04 27.87 27.59 26.67 0.23 0.06 – 1.2 3.6

05 27.88 27.73 26.65 0.19 0.09 – 6.8 0.7

06 27.29 27.28 26.62 –0.27 –0.19 – –12.0 –9.6

07 26.65 26.79 26.60 –0.42 –0.33 – –21.3 –20.1

08 26.55 26.50 26.60 –0.21 –0.31 – –25.6 –21.8

09 26.24 26.28 26.61 –0.38 –0.38 – –14.8 –14.4

10 26.08 26.04 26.60 –0.55 –0.57 – –2.5 –4.3

11 25.74 25.85 26.57 –0.79 –0.71 – 2.6 3.3

12 25.83 25.88 26.56 –0.71 –0.66 – 10.3 7.3
47

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1883 01 26.12 26.09 26.59 –0.42 –0.50 – 6.0 7.9

02 26.27 26.38 26.63 –0.45 –0.40 – 9.1 –0.3

03 26.86 26.88 26.66 –0.27 –0.27 – –25.3 –6.8

04 27.54 27.36 26.68 –0.10 –0.17 – 14.4 4.4

05 27.49 27.50 26.72 –0.20 –0.15 – 13.9 11.4

06 27.48 27.42 26.77 –0.08 –0.06 – 3.4 2.6

07 27.21 27.19 26.81 0.14 0.07 – –10.2 –3.9

08 26.85 26.87 26.85 0.09 0.07 – 1.4 –3.9

09 26.58 26.58 26.89 –0.04 –0.08 – –8.2 –2.6

10 26.32 26.41 26.92 –0.31 –0.19 – 4.8 1.7

11 26.43 26.41 26.97 –0.10 –0.15 – 5.2 0.0

12 26.44 26.45 27.01 –0.10 –0.09 – –15.2 –9.4

1884 01 26.47 26.53 27.03 –0.07 –0.05 – –12.5 –11.3

02 26.75 26.81 27.05 0.03 0.03 – –5.0 –3.3

03 27.26 27.33 27.07 0.13 0.17 – 9.4 –0.4

04 28.03 27.90 27.12 0.39 0.37 – –15.4 –5.0

05 28.26 28.03 27.17 0.57 0.38 – 1.3 –0.9

06 27.55 27.72 27.21 –0.01 0.25 – 9.1 4.1

07 27.51 27.41 27.24 0.44 0.30 – –3.0 –0.5

08 27.08 27.15 27.26 0.32 0.35 – –5.0 –5.0

09 26.94 27.00 27.28 0.32 0.34 – –7.0 –3.7

10 27.02 26.98 27.27 0.39 0.38 – 4.2 0.0

11 26.95 26.96 27.26 0.42 0.41 – –1.4 –2.8

12 26.93 26.88 27.27 0.39 0.34 – –12.6 –10.7

1885 01 26.70 26.84 27.28 0.16 0.26 – –16.3 –10.9

02 27.03 27.04 27.27 0.31 0.26 – 1.6 –2.0

03 27.38 27.39 27.29 0.25 0.23 – 5.1 2.8

04 27.75 27.80 27.33 0.11 0.27 – –0.5 –0.1

05 28.30 28.05 27.36 0.61 0.41 – –4.3 –5.9

06 27.85 27.83 27.41 0.29 0.36 – –14.4 –9.5

07 27.30 27.42 27.44 0.23 0.30 – –5.0 –8.5

08 27.21 27.25 27.43 0.45 0.45 – –9.5 –7.0

09 27.27 27.30 27.41 0.65 0.64 – –4.0 –8.8

10 27.45 27.41 27.38 0.82 0.81 – –17.8 –13.9

11 27.46 27.50 27.32 0.93 0.94 – –15.9 –11.1

12 27.61 27.36 27.22 1.07 0.82 – 5.2 –1.5

1886 01 26.75 26.95 27.13 0.21 0.36 – –0.6 1.4

02 26.67 26.81 27.03 –0.05 0.03 – 1.6 1.4

03 27.15 27.09 26.90 0.02 –0.06 – 2.9 3.0

04 27.40 27.24 26.75 –0.24 –0.28 – 4.5 4.5

05 27.02 27.06 26.58 –0.67 –0.59 – 6.0 5.4 LN start

06 26.79 26.71 26.39 –0.77 –0.76 – 5.0 5.9 LN

07 26.25 26.29 26.25 –0.82 –0.83 – 7.4 8.4 LN

08 25.85 25.87 26.18 –0.91 –0.93 – 13.6 12.0 LN

09 25.54 25.63 26.10 –1.08 –1.03 – 13.5 13.5 LN

10 25.59 25.51 26.02 –1.04 –1.10 – 13.4 12.7 LN

11 25.31 25.34 25.97 –1.22 –1.22 – 10.5 12.2 LN peak 1 (M)

12 25.15 25.38 25.97 –1.39 –1.16 – 14.4 12.9 LN
48

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1887 01 25.90 25.67 26.00 –0.64 –0.91 – 12.2 12.5 LN

02 25.74 25.87 26.04 –0.98 –0.91 – 11.0 11.1 LN

03 26.08 26.12 26.09 –1.05 –1.03 – 10.0 10.1 LN peak 2 (M)

04 26.59 26.50 26.17 –1.05 –1.03 – 9.4 6.1 LN peak 2 (M)

05 26.72 26.79 26.27 –0.97 –0.86 – –4.3 1.5 LN

06 27.12 26.91 26.39 –0.44 –0.56 – 5.0 2.6 LN end

07 26.68 26.68 26.54 –0.39 –0.43 – 4.8 4.8

08 26.25 26.40 26.60 –0.51 –0.41 – 4.6 4.8

09 26.41 26.42 26.74 –0.21 –0.24 – 5.1 4.9

10 26.61 26.58 26.86 –0.02 –0.02 – 4.8 2.4

11 26.69 26.68 26.99 0.16 0.13 – –5.3 –0.2

12 26.74 26.73 27.10 0.20 0.19 – 5.2 0.5

1888 01 26.73 26.91 27.19 0.19 0.32 – –3.0 –0.8

02 27.42 27.31 27.30 0.70 0.53 – –2.2 –4.8 EN start

03 27.66 27.70 27.40 0.53 0.55 – –11.7 –12.3 EN peak 1 (W)

04 28.07 28.04 27.50 0.43 0.51 – –23.6 –17.2 EN

05 28.34 28.21 27.66 0.65 0.57 – –9.8 –14.8 EN

06 28.09 28.08 27.81 0.53 0.61 – –16.0 –14.6 EN

07 27.78 27.86 27.95 0.71 0.75 – –16.7 –14.6 EN

08 27.80 27.68 28.06 1.04 0.88 – –8.9 –11.0 EN

09 27.33 27.66 28.11 0.71 1.00 – –9.4 –10.6 EN

10 28.16 28.13 28.14 1.53 1.53 – –14.7 –12.9 EN

11 28.86 28.54 28.14 2.33 1.98 – –12.6 –10.6 EN peak 2 (S)

12 28.26 28.49 28.12 1.72 1.95 – –2.4 –10.8 EN

1889 01 28.56 28.41 28.05 2.02 1.82 – –25.9 –14.0 EN

02 28.24 28.28 27.92 1.52 1.51 – –1.7 –14.2 EN

03 28.09 28.16 27.78 0.96 1.01 – –27.5 –14.3 EN

04 28.23 28.19 27.60 0.59 0.66 – –0.5 –7.6 EN end

05 28.19 28.10 27.35 0.50 0.45 – –1.9 4.4

06 27.78 27.56 27.09 0.22 0.09 – 22.0 10.9

07 26.47 26.65 26.78 –0.60 –0.47 – 1.6 6.8

08 25.88 26.02 26.44 –0.88 –0.79 – 2.1 4.2 LN start

09 25.83 25.74 26.21 –0.79 –0.92 – 11.1 7.1 LN

10 25.42 25.56 26.06 –1.21 –1.04 – 4.2 10.6 LN

11 25.57 25.48 25.94 –0.96 –1.08 – 23.0 18.1 LN

12 25.34 25.09 25.85 –1.20 –1.45 – 22.0 22.0 LN

1890 01 24.09 24.54 25.80 –2.45 –2.04 – 20.8 18.7 LN peak 1 (VS)

02 24.65 24.88 25.78 –2.07 –1.90 – 11.0 14.3 LN

03 26.11 25.88 25.75 –1.02 –1.28 – 14.3 11.6 LN

04 26.63 26.56 25.73 –1.01 –0.97 – 6.9 7.9 LN

05 26.87 26.80 25.73 –0.82 –0.85 – 3.6 5.0 LN

06 26.82 26.70 25.76 –0.74 –0.77 – 5.8 3.2 LN

07 26.30 26.23 25.87 –0.77 –0.89 – –2.3 –0.5 LN

08 25.50 25.69 26.03 –1.26 –1.11 – –3.1 0.2 LN

09 25.46 25.47 26.15 –1.16 –1.19 – 9.3 4.8 LN peak 2 (M)

10 25.47 25.50 26.25 –1.16 –1.11 – 3.6 4.8 LN

11 25.58 25.63 26.35 –0.95 –0.93 – 2.6 2.4 LN

12 25.90 25.88 26.45 –0.64 –0.66 – 0.6 4.9 LN end
49

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1891 01 26.13 26.17 26.54 –0.41 –0.42 – 15.6 7.1

02 26.51 26.59 26.64 –0.21 –0.19 – –3.6 –0.3

03 27.19 27.20 26.75 0.06 0.05 – –9.5 –4.5

04 27.92 27.76 26.85 0.28 0.23 – 4.5 –0.2

05 27.99 27.97 26.95 0.30 0.32 – –0.3 0.6

06 27.97 27.82 27.03 0.41 0.35 – –1.5 –2.4

07 27.34 27.40 27.05 0.27 0.28 – –6.3 –5.8

08 26.93 26.97 27.05 0.17 0.17 – –8.9 –8.7

09 26.67 26.74 27.02 0.05 0.09 – –10.6 –7.4

10 26.70 26.70 26.97 0.07 0.09 – 0.6 –3.5

11 26.71 26.68 26.90 0.18 0.12 – –4.7 –3.3

12 26.60 26.50 26.83 0.06 –0.04 – –4.5 –2.8

1892 01 26.08 26.30 26.76 –0.46 –0.29 – 2.7 –2.3

02 26.42 26.40 26.70 –0.30 –0.38 – –10.2 –1.7

03 26.68 26.73 26.63 –0.45 –0.43 – 11.1 4.7

04 27.12 27.02 26.53 –0.52 –0.51 – 6.9 8.7

05 27.14 27.13 26.40 –0.55 –0.52 – 10.0 11.6

06 27.12 27.00 26.28 –0.44 –0.48 – 19.6 14.2

07 26.60 26.64 26.20 –0.47 –0.47 – 7.4 10.1

08 26.25 26.20 26.13 –0.51 –0.61 – 5.9 6.4 LN start

09 25.68 25.70 26.07 –0.94 –0.96 – 6.3 6.8 LN

10 25.19 25.27 26.02 –1.44 –1.33 – 8.5 5.7 LN

11 25.03 25.17 25.96 –1.50 –1.39 – –0.7 2.7 LN peak 1 (M)

12 25.41 25.30 25.91 –1.13 –1.24 – 3.7 4.5 LN

1893 01 25.35 25.43 25.86 –1.19 –1.16 – 11.3 8.5 LN

02 25.60 25.64 25.80 –1.12 –1.14 – 7.7 6.3 LN

03 26.02 26.03 25.77 –1.11 –1.13 – –1.4 1.5 LN

04 26.47 26.38 25.77 –1.17 –1.15 – 1.2 –0.6 LN peak 2 (M)

05 26.55 26.52 25.79 –1.14 –1.13 – –3.5 1.2 LN

06 26.50 26.37 25.81 –1.06 –1.11 – 10.7 8.0 LN

07 25.91 25.98 25.82 –1.16 –1.14 – 14.0 11.6 LN

08 25.58 25.64 25.83 –1.18 –1.17 – 7.8 8.8 LN

09 25.48 25.48 25.84 –1.14 –1.18 – 5.7 6.8 LN

10 25.37 25.39 25.86 –1.26 –1.21 – 7.9 6.0 LN peak 3 (M)

11 25.35 25.42 25.89 –1.18 –1.14 – 2.6 3.7 LN

12 25.59 25.51 25.92 –0.95 –1.03 – 1.6 5.8 LN

1894 01 25.49 25.55 25.95 –1.05 –1.04 – 17.5 11.7 LN peak 4 (M)

02 25.63 25.74 25.99 –1.09 –1.04 – 10.0 10.8 LN peak 4 (M)

03 26.20 26.22 26.01 –0.93 –0.94 – 5.6 4.6 LN

04 26.85 26.69 26.04 –0.79 –0.83 – –3.0 –1.4 LN

05 26.87 26.86 26.08 –0.82 –0.79 – –5.1 –3.7 LN

06 26.85 26.73 26.12 –0.71 –0.74 – –1.5 –2.6 LN

07 26.34 26.40 26.16 –0.73 –0.72 – –2.3 –3.0 LN

08 26.07 26.03 26.20 –0.69 –0.77 – –5.7 –3.8 LN

09 25.65 25.82 26.25 –0.97 –0.84 – –1.6 –1.8 LN peak 5 (W)

10 25.91 25.80 26.31 –0.72 –0.80 – 1.8 2.3 LN

11 25.73 25.87 26.38 –0.80 –0.69 – 7.2 4.1 LN

12 26.11 25.95 26.45 –0.43 –0.59 – 0.1 3.3 LN
50

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1895 01 25.85 26.02 26.50 –0.69 –0.56 – 5.6 3.6 LN end

02 26.28 26.32 26.58 –0.44 –0.46 – 3.0 2.8

03 26.86 26.90 26.69 –0.27 –0.26 – –0.3 –1.2

04 27.60 27.47 26.80 –0.04 –0.05 – –7.1 –5.7

05 27.83 27.68 26.90 0.14 0.04 – –8.2 –7.1

06 27.47 27.43 27.00 –0.09 –0.04 – –4.7 –4.5

07 26.96 27.16 27.08 –0.11 0.04 – –0.4 –3.0

08 27.23 27.15 27.14 –0.47 0.35 – –6.3 –4.3

09 27.17 27.16 27.18 0.55 0.50 – –4.0 –5.0

10 27.05 27.09 27.21 0.42 0.49 – –5.6 –6.0

11 27.10 27.08 27.22 0.57 0.52 – –8.6 –6.6

12 27.07 27.00 27.22 0.53 0.46 – –3.5 –3.6

1896 01 26.74 26.85 27.25 0.20 0.27 – 1.3 1.0

02 26.85 26.96 27.31 0.13 0.19 – 4.9 1.2

03 27.41 27.36 27.36 0.28 0.20 – –6.3 –4.1

04 27.76 27.69 27.42 0.12 0.16 – –8.8 –16.5

05 27.82 27.72 27.50 0.13 0.08 – –42.2 –31.0

06 27.48 27.61 27.59 –0.08 0.14 – –30.6 –31.0

07 27.66 27.68 27.69 0.59 0.57 – –20.6 –23.6 EN start

08 27.92 27.82 27.78 1.16 1.02 – –22.4 –21.1 EN

09 27.79 27.83 27.84 1.17 1.18 – –19.0 –19.9 EN

10 27.83 27.90 27.85 1.20 1.30 – –19.0 –17.2 EN

11 28.16 28.07 27.84 1.63 1.52 – –11.9 –14.3 EN

12 28.14 28.13 27.84 1.60 1.59 – –14.2 –13.2 EN peak (S)

1897 01 28.07 28.05 27.83 1.53 1.46 – –12.5 –11.7 EN

02 27.90 27.92 27.77 1.18 1.14 – –7.4 –11.0 EN

03 27.80 27.76 27.66 0.67 0.61 – –16.6 –14.6 EN end

04 27.55 27.65 27.54 –0.09 0.12 – –17.8 –17.3

05 27.69 27.65 27.38 0.00 0.00 – –16.9 –12.9

06 27.66 27.58 27.21 0.10 0.11 – 0.2 –4.7

07 27.29 27.24 27.05 0.22 0.13 – –2.3 –0.9

08 26.73 26.82 26.90 –0.03 0.01 – 0.8 –0.1

09 26.51 26.48 26.77 –0.11 –0.18 – 0.2 0.8

10 26.17 26.22 26.70 –0.46 –0.38 – 1.8 –1.1

11 26.04 26.11 26.66 –0.49 –0.45 – –8.0 –1.0

12 26.19 26.12 26.64 –0.35 –0.42 – 10.3 4.9

1898 01 26.07 26.13 26.60 –0.47 –0.46 – 7.0 7.7

02 26.19 26.23 26.54 –0.53 –0.55 – 6.3 9.7

03 26.47 26.57 26.52 –0.66 –0.58 – 19.2 14.0

04 27.16 27.02 26.53 –0.48 –0.51 – 11.1 9.9

05 27.28 27.28 26.54 –0.41 –0.37 – –1.9 1.3

06 27.40 27.17 26.52 –0.16 –0.30 – –2.3 –0.1

07 26.59 26.67 26.49 –0.48 –0.44 – 6.1 3.0

08 26.11 26.34 26.48 –0.65 –0.46 – 2.1 3.4

09 26.56 26.41 26.48 –0.06 –0.25 – 3.2 2.0

10 26.40 26.34 26.50 –0.23 –0.26 – –0.7 –0.2

11 26.00 26.05 26.54 –0.53 –0.51 – –2.7 –1.6

12 25.80 25.86 26.58 –0.74 –0.68 – –0.4 2.4
51

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1899 01 25.83 25.88 26.62 –0.71 –0.71 – 13.2 8.8

02 26.05 26.16 26.70 –0.67 –0.62 – 9.1 11.3

03 26.69 26.72 26.79 –0.44 –0.44 – 13.8 10.3

04 27.43 27.25 26.87 –0.21 –0.16 – 4.5 3.9

05 27.90 27.75 27.00 0.21 0.11 – –7.4 –5.2

06 27.78 27.67 27.18 0.22 0.20 – –10.4 –8.5

07 27.20 27.42 27.36 0.13 0.31 – –5.6 –7.9

08 27.51 27.35 27.54 0.75 0.55 – –10.1 –6.9 EN start

09 27.18 27.38 27.68 0.56 0.73 – –1.6 –1.8 EN

10 27.66 27.61 27.79 1.03 1.01 – 6.1 6.6 EN

11 27.94 27.91 27.85 1.41 1.35 – 15.8 8.7 EN

12 28.09 28.03 27.90 1.55 1.49 – –3.0 0.6 EN peak 1 (M)

1900 01 27.99 28.03 27.96 1.45 1.45 – –7.3 –0.6 EN

02 28.06 28.09 28.00 1.34 1.31 – –6.5 –11.4 EN

03 28.25 28.25 28.01 1.12 1.09 – –25.3 –19.0 EN

04 28.43 28.38 28.00 0.79 0.85 – –18.7 –17.5 EN

05 28.40 28.42 27.93 0.71 0.78 – –7.4 –1.9 EN

06 28.45 28.32 27.84 0.89 0.85 – 26.1 13.7 EN

07 27.97 28.01 27.78 0.90 0.90 – 10.0 13.5 EN peak 2 (W)

08 27.65 27.65 27.71 0.89 0.89 – 7.8 2.3 EN

09 27.31 27.36 27.63 0.69 0.70 – –16.6 –10.7 EN

10 27.15 27.10 27.56 0.52 0.50 – –17.2 –14.3 EN end

11 26.79 26.98 27.50 0.26 0.42 – –6.0 –8.7

12 27.19 27.14 27.42 0.65 0.61 – –5.5 –4.3

1901 01 27.40 27.26 27.34 0.86 0.68 – –0.1 –0.7

02 27.06 27.21 27.25 0.34 0.43 – 3.0 3.8

03 27.30 27.33 27.16 0.17 0.17 – 9.4 6.6

04 27.64 27.57 27.10 0.00 0.04 – 4.5 4.5

05 27.68 27.61 27.04 –0.01 –0.04 – –0.3 5.9

06 27.43 27.37 26.98 –0.13 –0.10 – 19.6 13.4

07 26.93 26.95 26.89 –0.14 –0.17 – 14.6 14.7

08 26.50 26.60 26.81 –0.26 –0.21 – 9.8 4.6

09 26.45 26.46 26.77 –0.17 –0.20 – –16.0 –11.1

10 26.42 26.39 26.77 –0.21 –0.22 – –22.1 –17.2

11 26.26 26.30 26.82 –0.27 –0.26 – –8.6 –10.3

12 26.24 26.21 26.89 –0.30 –0.33 – –1.9 1.2

1902 01 26.08 26.23 27.00 –0.46 –0.36 – 17.0 7.5

02 26.50 26.52 27.14 –0.22 –0.26 – –2.2 6.1

03 26.99 27.11 27.28 –0.14 –0.04 – 11.6 7.2

04 27.97 27.82 27.42 0.33 0.29 – 7.8 11.5

05 28.34 28.28 27.57 0.65 0.63 – 7.6 6.4 EN start

06 28.45 28.48 27.73 0.89 1.01 – 2.6 3.6 EN

07 28.67 28.47 27.87 1.60 1.36 – 1.6 –0.8 EN

08 28.09 28.26 28.00 1.33 1.46 – –8.9 –8.5 EN

09 28.19 28.15 28.09 1.57 1.49 – –17.8 –13.0 EN

10 28.13 28.16 28.15 1.50 1.56 – –7.4 –9.0 EN

11 28.19 28.12 28.13 1.66 1.57 – –3.4 –4.3 EN peak (S)

12 27.98 28.02 28.08 1.44 1.48 – –3.0 –4.7 EN
52

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1903 01 27.91 27.87 27.98 1.37 1.29 – –9.2 –7.9 EN

02 27.69 27.84 27.84 0.97 1.06 – –10.2 –3.0 EN

03 28.05 27.98 27.69 0.92 0.83 – 17.6 10.7 EN

04 28.13 28.02 27.53 0.49 0.50 – 17.7 15.2 EN end

05 27.77 27.91 27.36 0.08 0.27 – 7.6 8.1

06 27.98 27.62 27.16 0.42 0.15 – –0.6 3.1

07 26.74 27.00 26.98 –0.33 –0.11 – 6.1 2.9

08 26.55 26.50 26.82 –0.21 –0.31 – 0.1 3.8

09 26.15 26.29 26.68 –0.47 –0.37 – 8.7 5.4

10 26.31 26.17 26.56 –0.32 –0.44 – 4.2 4.6

11 25.89 25.92 26.51 –0.64 –0.64 – 1.3 5.7 LN start

12 25.57 25.72 26.49 –0.97 –0.82 – 15.9 11.8 LN peak (W)

1904 01 25.84 25.81 26.53 –0.70 –0.78 – 14.6 15.1 LN

02 25.97 26.05 26.62 –0.75 –0.73 – 16.2 14.0 LN

03 26.40 26.46 26.68 –0.73 –0.70 – 9.4 16.7 LN

04 27.05 26.99 26.76 –0.59 –0.53 – 31.7 20.5 LN end

05 27.47 27.46 26.86 –0.22 –0.19 – 9.2 10.8

06 27.83 27.78 26.97 0.27 0.31 – –7.1 –3.5

07 27.98 27.80 27.11 0.91 0.69 – –8.9 –6.0

08 27.42 27.40 27.23 0.66 0.59 – 0.8 –1.8

09 26.76 27.15 27.37 0.14 0.49 – 0.2 0.6

10 27.65 27.22 27.49 1.02 0.62 – 1.2 –3.7 EN start

11 26.81 27.18 27.59 0.28 0.62 – –17.2 –7.7 EN

12 27.44 27.24 27.67 0.90 0.70 – 2.6 –5.3 EN

1905 01 27.26 27.36 27.69 0.72 0.78 – –9.2 –8.2 EN

02 27.48 27.60 27.72 0.76 0.82 – –16.8 –18.3 EN peak 1 (W)

03 28.18 27.98 27.80 1.05 0.82 – –30.2 –30.0 EN peak 1 (W)

04 28.06 28.31 27.86 0.42 0.79 – –42.6 –38.2 EN

05 28.94 28.56 27.90 1.25 0.91 – –37.4 –37.2 EN

06 28.28 28.39 27.94 0.72 0.92 – –31.4 –30.4 EN

07 28.05 28.08 27.96 0.98 0.96 – –21.3 –20.4 EN

08 27.92 28.02 27.97 1.16 1.22 – –7.6 –10.9 EN

09 28.18 28.03 27.96 1.56 1.38 – –7.0 –6.8 EN peak 2 (M)

10 27.85 27.84 27.96 1.22 1.24 – –5.6 –9.0 EN

11 27.48 27.64 27.93 0.95 1.09 – –17.9 –13.6 EN

12 27.76 27.62 27.86 1.22 1.08 – –13.1 –11.9 EN

1906 01 27.47 27.54 27.79 0.93 0.95 – –3.5 –6.9 EN

02 27.44 27.60 27.68 0.72 0.83 – –7.4 –5.9 EN

03 28.06 27.95 27.52 0.93 0.79 – –5.2 –6.7 EN

04 28.22 28.10 27.35 0.58 0.57 – –8.8 –5.4 EN end

05 27.88 27.95 27.22 0.19 0.31 – 1.3 –2.5

06 27.83 27.57 27.10 0.27 0.10 – –3.9 0.1

07 26.73 26.95 26.97 –0.34 –0.17 – 6.8 6.3

08 26.51 26.42 26.86 –0.25 –0.38 – 15.5 14.0

09 25.94 26.07 26.77 –0.68 –0.59 – 18.3 15.3

10 25.87 26.00 26.67 –0.76 –0.60 – 9.1 14.6

11 26.33 26.15 26.61 –0.20 –0.41 – 21.7 14.3

12 26.07 26.12 26.57 –0.47 –0.42 – 4.7 9.1
53

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1907 01 26.01 26.11 26.54 –0.53 –0.47 – 5.1 4.1

02 26.36 26.39 26.53 –0.36 –0.39 – 1.6 2.0

03 26.83 26.81 26.56 –0.30 –0.35 – –0.3 1.4

04 27.21 27.16 26.62 –0.43 –0.37 – 4.5 4.7

05 27.39 27.32 26.65 –0.30 –0.33 – 10.0 8.2

06 27.28 27.16 26.67 –0.28 –0.31 – 8.3 5.6

07 26.68 26.72 26.70 –0.39 –0.40 – –4.3 –2.1

08 26.22 26.50 26.73 –0.54 –0.30 – –8.2 –5.1

09 26.88 26.62 26.74 0.26 –0.04 – 0.2 –1.8

10 26.48 26.56 26.73 –0.15 –0.08 – 0.6 –0.2

11 26.40 26.44 26.73 –0.13 –0.12 – –2.0 1.4

12 26.49 26.42 26.74 –0.05 –0.12 – 8.8 1.3

1908 01 26.30 26.48 26.75 –0.24 –0.11 – –10.6 –1.2

02 26.83 26.65 26.75 0.11 –0.13 – 7.7 1.3

03 26.63 26.83 26.74 –0.50 –0.33 – 0.2 6.2

04 27.22 27.12 26.70 –0.42 –0.41 – 16.8 8.2

05 27.41 27.38 26.66 –0.28 –0.27 – –1.1 3.1

06 27.47 27.24 26.59 –0.09 –0.24 – –2.3 –0.9

07 26.59 26.78 26.55 –0.48 –0.33 – 2.2 1.9

08 26.48 26.45 26.51 –0.28 –0.36 – 5.3 7.6

09 26.23 26.29 26.47 –0.39 –0.37 – 17.7 12.2

10 26.23 26.12 26.47 –0.40 –0.49 – 7.9 9.0

11 25.78 25.81 26.47 –0.75 –0.75 – 2.6 1.9 LN start

12 25.43 25.73 26.44 –1.11 –0.81 – –5.5 –2.7 LN peak (W)

1909 01 26.29 25.97 26.39 –0.25 –0.61 – –2.5 –3.4 LN

02 25.88 26.19 26.35 –0.84 –0.59 – –3.2 –2.3 LN

03 26.72 26.60 26.31 –0.41 –0.55 – –0.3 –4.6 LN end

04 27.09 27.10 26.26 –0.55 –0.43 – –14.5 –6.8

05 27.50 27.17 26.21 –0.19 –0.48 – 2.1 3.1

06 26.59 26.73 26.18 –0.97 –0.75 – 22.8 14.6 LN start

07 26.22 26.23 26.16 –0.85 –0.88 – 10.7 13.5 LN peak 1 (W)

08 25.90 25.98 26.14 –0.86 –0.82 – 9.8 7.8 LN

09 25.90 25.80 26.14 –0.72 –0.86 – 0.8 3.9 LN

10 25.49 25.51 26.11 –1.14 –1.10 – 4.2 4.6 LN

11 25.15 25.33 26.05 –1.38 –1.23 – 9.2 6.8 LN peak 2 (M)

12 25.51 25.46 26.01 –1.03 –1.08 – 4.7 6.1 LN

1910 01 25.65 25.73 26.01 –0.89 –0.85 – 5.6 7.8 LN

02 26.12 26.09 26.02 –0.60 –0.69 – 15.2 12.2 LN

03 26.46 26.41 26.01 –0.67 –0.75 – 12.7 11.5 LN

04 26.59 26.53 26.00 –1.05 –1.00 – 5.3 6.0 LN

05 26.46 26.54 26.06 –1.23 –1.11 – 0.5 7.1 LN peak 3 (M)

06 26.65 26.53 26.12 –0.91 –0.94 – 22.0 16.3 LN

07 26.35 26.33 26.15 –0.72 –0.78 – 20.5 18.2 LN

08 25.98 25.94 26.17 –0.78 –0.86 – 9.8 13.9 LN

09 25.46 25.68 26.17 –1.16 –0.98 – 15.3 12.7 LN peak 4 (W)

10 25.80 25.80 26.17 –0.83 –0.81 – 10.3 13.9 LN

11 26.13 26.00 26.19 –0.40 –0.56 – 19.7 16.4 LN

12 25.95 26.01 26.22 –0.59 –0.53 – 15.9 13.7 LN
54

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1911 01 26.01 26.04 26.26 –0.53 –0.55 – 3.2 6.0 LN

02 26.18 26.20 26.32 –0.54 –0.58 – 1.6 2.5 LN

03 26.44 26.43 26.40 –0.69 –0.73 – 3.5 2.7 LN

04 26.66 26.65 26.51 –0.98 –0.88 – 2.0 –0.2 LN peak 5 (W)

05 26.82 26.84 26.62 –0.87 –0.81 – –8.2 –10.3 LN end

06 27.05 26.98 26.74 –0.51 –0.49 – –12.0 –11.3

07 27.01 26.92 26.90 –0.06 –0.20 – –12.8 –12.4

08 26.59 26.79 27.04 –0.17 –0.01 – –12.1 –11.5

09 26.97 26.87 27.17 0.35 0.21 – –8.8 –10.4

10 26.93 27.08 27.30 0.30 0.48 – –11.7 –9.9

11 27.50 27.37 27.41 0.97 0.81 – –7.3 –6.9 EN start

12 27.55 27.68 27.47 1.01 1.15 – –1.4 –5.0 EN

1912 01 28.13 27.85 27.49 1.59 1.27 – –9.7 –9.5 EN peak (M)

02 27.59 27.82 27.49 0.87 1.04 – –17.3 –13.3 EN

03 27.95 27.96 27.49 0.82 0.81 – –9.0 –14.1 EN

04 28.35 28.13 27.47 0.71 0.61 – –21.1 –16.1 EN end

05 27.87 27.88 27.42 0.18 0.24 – –13.0 –13.4

06 27.44 27.47 27.34 –0.12 0.00 – –6.3 –6.5

07 27.12 27.04 27.20 0.05 –0.08 – –0.4 –3.7

08 26.48 26.73 27.10 –0.28 –0.07 – –7.6 –4.9

09 26.85 26.70 27.05 0.23 0.04 – –4.0 –5.9

10 26.60 26.72 26.97 –0.03 0.12 – –8.0 –4.4

11 26.82 26.59 26.91 0.29 0.03 – 2.6 –2.7

12 26.10 26.35 26.90 –0.44 –0.19 – –8.0 –4.2

1913 01 26.38 26.45 26.90 –0.16 –0.14 – –3.5 –5.0

02 26.94 26.92 26.91 0.22 0.14 – –5.0 –3.1

03 27.42 27.20 26.92 0.29 0.04 – 1.3 –2.2

04 27.00 27.25 26.93 –0.64 –0.28 – –6.3 –4.9

05 27.58 27.42 26.96 –0.11 –0.22 – –8.2 –6.7

06 27.53 27.43 27.04 –0.03 –0.04 – –3.9 –4.4

07 27.08 27.12 27.13 0.01 0.01 – –1.7 –3.7

08 26.79 26.87 27.20 0.03 0.06 – –7.6 –6.6

09 26.80 26.79 27.23 0.18 0.13 – –9.4 –8.9

10 26.76 26.94 27.30 0.13 0.34 – –9.2 –9.9

11 27.45 27.27 27.37 0.92 0.72 – –11.9 –10.0 EN start

12 27.43 27.40 27.39 0.89 0.86 – –7.0 –7.8 EN peak (W)

1914 01 27.28 27.39 27.43 0.74 0.80 – –5.4 –4.0 EN

02 27.56 27.50 27.50 0.84 0.72 – 2.0 2.0 EN

03 27.58 27.80 25.57 0.45 0.64 – 9.4 1.6 EN

04 28.46 28.09 27.60 0.82 0.57 – –14.5 –5.0 EN end

05 27.87 27.99 27.59 0.18 0.35 – –0.3 –8.0

06 27.77 27.79 27.57 0.21 0.32 – –16.8 –13.0

07 27.75 27.77 27.57 0.68 0.65 – –18.0 –17.5

08 27.80 27.70 27.57 1.04 0.89 – –17.2 –16.2

09 27.43 27.41 27.57 0.81 0.76 – –12.4 –12.7

10 26.99 27.09 27.57 0.36 0.49 – –8.6 –10.4

11 26.96 27.05 27.58 0.43 0.49 – –11.9 –8.5

12 27.27 27.42 27.64 0.73 0.70 – –1.4 –9.1 EN start
55

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1915 01 27.46 27.40 27.67 0.92 0.82 – –21.6 –11.7 EN peak 1 (W)

02 27.41 27.51 27.61 0.69 0.73 – –2.2 –11.6 EN

03 27.75 27.79 27.55 0.62 0.63 – –20.4 –15.2 EN

04 28.24 28.15 27.53 0.60 0.63 – –17.8 –17.1 EN

05 28.38 28.45 27.51 0.69 0.80 – –12.2 –8.9 EN

06 28.78 28.31 27.45 1.22 0.84 – 6.6 3.8 EN peak 2 (W) end

07 27.29 27.57 27.38 0.22 0.46 – 14.0 10.5

08 26.93 27.02 27.28 0.17 0.22 – 7.2 9.0

09 26.92 26.94 27.19 0.30 0.28 – 7.5 6.2

10 26.97 26.84 27.10 0.34 0.23 – 2.4 –0.6

11 26.51 26.59 27.02 –0.02 0.03 – –14.6 –4.3

12 26.36 26.42 26.93 –0.18 –0.12 – 9.8 2.7

1916 01 26.46 26.36 26.82 –0.08 –0.23 – 5.6 4.4

02 26.16 26.38 26.71 –0.56 –0.40 – –3.6 –2.0

03 26.72 26.69 26.58 –0.41 –0.47 – –6.3 –4.2

04 27.14 27.16 26.45 –0.50 –0.37 – –0.5 –0.1

05 27.64 27.44 26.32 –0.05 –0.21 – 6.8 5.6

06 27.32 27.10 26.19 –0.24 –0.37 – 9.1 12.7

07 26.12 26.24 26.07 –0.95 –0.88 – 25.7 19.2 LN start

08 25.39 25.57 25.99 –1.37 –1.23 – 16.2 15.7 LN

09 25.39 25.39 25.96 –1.23 –1.27 – 4.5 7.8 LN

10 25.37 25.27 25.97 –1.26 –1.34 – 6.1 6.6 LN

11 24.93 25.05 25.98 –1.60 –1.51 – 9.8 10.3 LN

12 24.95 24.96 25.99 –1.59 –1.58 – 15.4 11.4 LN peak (S)

1917 01 25.02 25.14 26.05 –1.52 –1.45 – 5.1 8.9 LN

02 25.56 25.69 26.16 –1.16 –1.09 – 10.0 6.6 LN

03 26.62 26.57 26.29 –0.51 –0.59 – 18.1 17.0 LN end

04 27.48 27.29 26.40 –0.16 –0.24 – 21.8 20.9

05 27.57 27.57 26.51 –0.12 –0.08 – 21.8 21.7

06 27.65 27.51 26.60 0.09 0.04 – 21.2 23.1

07 27.18 27.26 26.67 0.11 0.15 – 28.3 28.2

08 27.03 26.99 26.72 0.27 0.19 – 34.8 31.9

09 26.73 26.82 26.72 0.11 0.16 – 29.7 27.4

10 26.77 26.63 26.70 0.14 0.02 – 15.2 20.3

11 26.23 26.28 26.69 –0.30 –0.28 – 21.0 19.9

12 25.87 25.93 26.71 –0.67 –0.61 – 22.5 20.2

1918 01 25.74 25.82 26.73 –0.80 –0.76 – 14.6 17.1

02 25.94 25.98 26.73 –0.78 –0.80 – 16.6 11.5

03 26.30 26.44 26.74 –0.83 –0.72 – –2.0 7.4

04 27.21 27.11 26.80 –0.43 –0.42 – 16.8 12.1

05 27.70 27.67 26.90 0.01 –0.09 – 10.0 8.0

06 28.06 27.74 27.06 0.05 0.05 – –4.7 –3.4

07 27.15 27.34 27.24 0.08 0.11 – –14.1 –9.3

08 27.00 27.08 27.43 0.24 0.28 – –4.4 –5.8

09 27.16 27.25 27.59 0.54 0.59 – –8.2 –6.5 EN start

10 27.66 27.59 27.72 1.03 0.99 – –5.0 –4.2 EN

11 27.89 27.83 27.81 1.36 1.28 – 1.3 –2.6 EN

12 27.89 27.96 27.85 1.35 1.43 – –8.0 –7.4 EN
56

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1919 01 28.18 28.06 27.88 1.64 1.48 – –14.9 –12.3 EN peak 1 (M)

02 28.00 28.09 27.92 1.28 1.31 – –11.2 –12.5 EN

03 28.16 28.20 27.95 1.03 1.04 – –12.8 –10.0 EN

04 28.46 28.39 27.92 0.82 0.87 – –3.0 –6.6 EN

05 28.49 28.43 27.82 0.80 0.79 – –7.4 –7.1 EN

06 28.29 28.18 27.71 0.73 0.71 – –10.4 –9.3 EN

07 27.63 27.76 27.63 0.56 0.65 – –8.9 –8.8 EN

08 27.50 27.47 27.57 0.74 0.67 – –6.9 –7.1 EN peak 2 (W)

09 27.26 27.22 27.52 0.64 0.57 – –5.8 –7.3 EN end

10 26.87 26.82 27.47 0.24 0.22 – –10.5 –9.5

11 26.29 26.60 27.40 –0.24 0.04 – –11.3 –10.6

12 26.93 26.84 27.36 0.39 0.31 – –9.1 –6.9

1920 01 27.22 27.19 27.33 0.68 0.60 – 1.8 –1.8

02 27.37 27.44 27.30 0.65 0.66 – –1.7 –1.4

03 27.79 27.64 27.27 0.66 0.49 – –4.1 –2.4

04 27.61 27.67 27.27 –0.03 0.14 – 0.3 –1.6

05 27.66 27.73 27.30 –0.03 0.08 – –2.7 0.4

06 27.98 27.75 27.30 0.42 0.28 – 6.6 5.0

07 27.37 27.43 27.27 0.30 0.32 – 9.4 7.7

08 27.01 27.10 27.22 0.25 0.30 – 5.3 6.3

09 27.02 27.07 27.09 0.40 0.41 – 5.1 2.8

10 27.22 27.01 26.99 0.59 0.41 – –4.3 –0.9

11 26.57 26.73 26.95 0.04 0.18 – –0.1 1.3

12 26.57 26.68 26.90 0.03 0.14 – 9.8 7.6

1921 01 27.01 26.71 26.86 0.47 0.13 – 10.8 9.5

02 26.25 26.34 26.82 –0.47 –0.44 – 6.7 8.3

03 25.84 26.29 26.79 –1.29 –0.87 – 8.9 4.4

04 27.22 26.81 26.75 –0.42 –0.72 – –7.1 –0.8

05 26.94 27.14 26.69 –0.75 –0.50 – 2.1 4.8

06 27.47 27.21 26.63 –0.09 –0.26 – 22.0 12.3

07 26.95 26.99 26.57 –0.12 –0.13 – 2.9 5.2

08 26.59 26.68 26.55 –0.17 –0.13 – –6.9 –1.5

09 26.58 26.63 26.63 –0.04 –0.03 – 5.1 3.3

10 26.77 26.44 26.69 0.14 –0.17 – 9.7 8.3

11 25.62 26.03 26.74 –0.91 –0.53 – 8.5 8.7

12 26.09 25.96 26.78 –0.45 –0.58 – 8.2 8.2

1922 01 26.04 26.22 26.76 –0.50 –0.37 – 8.0 8.3

02 26.69 26.69 26.73 –0.03 –0.09 – 9.1 8.0

03 27.33 27.15 26.71 0.20 –0.01 – 5.6 3.7

04 27.23 27.47 26.68 –0.41 –0.06 – –5.5 –2.6

05 28.09 27.67 26.70 0.40 0.02 – –5.1 –2.5

06 27.25 27.34 26.73 –0.31 –0.13 – 5.8 2.2

07 26.78 26.73 26.74 –0.29 –0.39 – 2.2 2.3

08 26.09 26.34 26.71 –0.67 –0.47 – –1.2 1.2

09 26.38 26.33 26.65 –0.24 –0.33 – 5.1 3.8

10 26.48 26.42 26.61 –0.15 –0.18 – 6.1 6.5

11 26.34 26.31 26.59 –0.19 –0.25 – 8.5 8.7

12 26.06 26.16 26.58 –0.48 –0.38 – 11.8 9.4
57

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1923 01 26.17 26.10 26.02 –0.37 –0.49 – 5.6 6.9

02 26.00 26.15 26.65 –0.72 –0.63 – 4.4 5.8

03 26.41 26.51 26.74 –0.72 –0.65 – 8.9 7.7

04 27.22 27.12 26.82 –0.42 –0.41 – 8.6 7.1

05 27.62 27.50 26.91 –0.07 –0.15 – 2.1 3.5

06 27.54 27.43 27.03 –0.02 –0.04 – 1.0 –1.9

07 27.03 27.17 27.13 –0.04 0.05 – –11.5 –10.1

08 27.07 27.14 27.22 0.31 0.34 – –18.5 –15.8

09 27.40 27.35 27.33 0.78 0.69 – –14.8 –13.6 EN start

10 27.52 27.49 27.41 0.89 0.89 – –6.2 –10.0 EN

11 27.52 27.50 27.40 0.99 0.98 – –12.6 –7.3 EN peak (W)

12 27.60 27.44 27.36 1.06 0.90 – 2.1 –3.5 EN

1924 01 27.04 27.27 27.30 0.50 0.68 – –5.4 –1.9 EN

02 27.39 27.37 27.23 0.67 0.59 – 1.1 –0.2 EN end

03 27.65 27.61 27.12 0.52 0.46 – 2.4 –2.4

04 27.75 27.54 27.01 0.11 0.02 – –15.4 –4.2

05 27.02 27.20 26.88 –0.67 –0.44 – 11.5 4.0

06 27.02 26.83 26.73 –0.54 –0.64 – 8.3 8.9 LN start

07 26.25 26.40 26.59 –0.82 –0.71 – 7.4 8.4 LN

08 26.09 26.08 26.49 –0.67 –0.72 – 10.4 9.1 LN peak 1 (W)

09 25.89 26.04 26.40 –0.73 –0.62 – 8.1 8.6 LN

10 26.28 26.00 26.34 –0.35 –0.60 – 7.9 8.9 LN

11 25.56 25.83 26.34 –0.97 –0.73 – 11.8 9.2 LN

12 25.93 25.74 26.38 –0.61 –0.80 – 5.2 7.0 LN peak 2 (W)

1925 01 25.55 25.83 26.46 –0.99 –0.76 – 5.6 7.6 LN

02 26.29 26.22 26.58 –0.43 –0.56 – 13.8 12.0 LN end

03 26.73 26.75 26.71 –0.40 –0.41 – 14.9 14.5

04 27.25 27.18 26.84 –0.39 –0.35 – 14.4 10.7

05 27.47 27.43 26.98 –0.22 –0.22 – –1.1 1.9

06 27.51 27.56 27.16 –0.05 0.09 – –4.7 –6.0

07 27.73 27.63 27.36 0.66 0.52 – –13.4 –10.6 EN start

08 27.55 27.59 27.54 0.79 0.79 – –10.8 –10.4 EN

09 27.52 27.54 27.68 0.90 0.89 – –6.4 –9.1 EN

10 27.58 27.59 27.82 0.95 0.98 – –12.9 –10.4 EN

11 27.66 27.77 27.93 1.13 1.22 – –9.3 –9.6 EN

12 28.19 28.04 28.02 1.65 1.50 – –7.0 –7.2 EN

1926 01 28.10 28.11 28.05 1.56 1.53 – –5.4 –8.1 EN peak (S)

02 28.06 28.17 28.04 1.34 1.39 – –14.5 –11.9 EN

03 28.44 28.43 27.98 1.31 1.28 – –13.3 –12.1 EN

04 28.78 28.67 27.90 1.14 1.15 – –7.1 –7.6 EN

05 28.69 28.61 27.79 1.00 0.97 – –2.7 –4.9 EN

06 28.29 28.28 27.66 0.73 0.81 – –7.1 –4.5 EN

07 27.86 27.76 27.53 0.79 0.65 – –1.0 –4.2 EN end

08 27.03 27.15 27.42 0.27 0.37 – –7.6 –3.7

09 26.68 26.68 27.32 0.06 0.03 – 1.4 –0.2

10 26.34 26.44 27.21 –0.29 –0.17 – 4.2 2.8

11 26.38 26.37 27.10 –0.15 –0.19 – 1.3 3.3

12 26.36 26.45 27.01 –0.18 –0.09 – 6.2 4.7
58

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1927 01 26.68 26.68 26.94 0.14 0.10 – 5.1 4.4

02 27.00 26.94 26.89 0.28 0.16 – 1.1 6.4

03 27.08 27.17 26.88 –0.05 0.01 – 18.1 11.1

04 27.50 27.34 26.90 –0.14 –0.19 – 6.9 9.5

05 27.28 27.40 26.94 –0.41 –0.25 – 6.0 6.8

06 27.54 27.32 26.97 –0.02 –0.15 – 8.3 7.2

07 26.92 27.04 27.00 –0.15 –0.08 – 6.1 3.9

08 26.78 26.77 27.02 0.02 –0.03 – –5.0 –1.1

09 26.60 26.75 27.01 –0.02 0.09 – –0.4 –2.5

10 27.00 26.80 27.01 0.37 0.20 – –4.3 –4.3

11 26.61 26.77 27.04 0.08 0.21 – –8.0 –3.2

12 26.84 26.84 27.05 0.30 0.30 – 7.7 –0.7

1928 01 27.05 26.98 27.06 0.51 0.39 – –10.1 –0.5

02 26.97 27.00 27.07 0.25 0.22 – 10.5 6.2

03 27.01 27.14 27.06 –0.12 –0.02 – 13.8 12.5

04 27.55 27.49 27.05 –0.09 –0.04 – 11.9 8.7

05 27.83 27.66 27.03 0.14 0.02 – –2.7 –0.4

06 27.43 27.49 27.01 –0.13 0.02 – –7.9 –4.7

07 27.25 27.13 26.97 0.18 0.02 – –0.4 0.3

08 26.59 26.76 26.93 –0.17 –0.04 – 9.8 6.8

09 26.62 26.61 26.93 0.00 –0.05 – 8.1 8.8

10 26.61 26.58 26.93 –0.02 –0.02 – 9.1 7.2

11 26.49 26.54 26.93 –0.04 –0.02 – 2.6 6.5

12 26.56 26.51 26.94 0.02 –0.03 – 11.8 10.6

1929 01 26.43 26.53 26.86 –0.11 –0.06 – 16.0 15.5

02 26.69 26.73 26.97 –0.03 –0.04 – 18.0 14.3

03 27.11 27.13 27.00 –0.02 –0.02 – 5.1 8.2

04 27.62 27.51 27.04 –0.02 –0.01 – 4.5 0.5

05 27.70 27.71 27.08 0.01 0.06 – –12.2 –4.7

06 27.81 27.63 27.12 0.25 0.16 – 1.0 –2.2

07 27.21 27.30 27.17 0.14 0.19 – 1.6 1.1

08 26.98 27.06 27.21 0.22 0.25 – 0.1 0.4

09 27.05 27.05 27.25 0.43 0.40 – –0.4 1.8

10 27.13 27.04 27.29 0.50 0.44 – 7.9 6.6

11 26.84 27.01 27.32 0.31 0.45 – 11.1 9.0

12 27.22 27.05 27.33 0.68 0.52 – 5.7 8.8

1930 01 26.93 27.06 27.36 0.39 0.47 – 12.7 9.7

02 27.15 27.20 27.41 0.43 0.42 – 7.7 7.5

03 27.55 27.61 27.48 0.42 0.45 – 1.8 1.9

04 28.18 27.94 27.55 0.54 0.41 – –3.8 –0.9

05 27.83 27.95 27.65 0.14 0.30 – 2.1 –1.3

06 27.95 27.90 27.75 0.39 0.43 – –5.5 –3.3

07 27.86 27.81 27.83 0.79 0.69 – –4.3 –4.0 EN start

08 27.56 27.76 27.91 0.80 0.95 – –1.8 –3.7 EN

09 28.04 27.88 27.99 1.42 1.22 – –7.0 –3.1 EN

10 27.87 28.06 28.05 1.24 1.45 – 3.6 0.5 EN

11 28.44 28.19 28.10 1.91 1.63 – 1.9 1.5 EN peak (S)

12 28.00 28.13 28.14 1.46 1.59 – –1.4 1.5 EN
59

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1931 01 28.07 28.06 28.14 1.53 1.48 – 7.0 –0.6 EN

02 28.10 28.18 28.11 1.38 1.40 – –14.9 –4.3 EN

03 28.44 28.43 28.01 1.31 1.27 – 5.6 1.2 EN

04 28.73 28.60 27.88 1.09 1.07 – 8.6 9.0 EN

05 28.49 28.47 27.74 0.80 0.82 – 13.1 13.4 EN

06 28.16 28.11 27.58 0.60 0.64 – 18.8 15.0 EN

07 27.63 27.61 27.43 0.56 0.50 – 9.4 9.4 EN end

08 27.02 27.00 27.29 0.26 0.20 – 0.1 3.7

09 26.33 26.55 27.19 –0.29 –0.11 – 5.1 –0.7

10 26.51 26.43 27.12 –0.12 –0.17 – –12.9 –6.4

11 26.38 26.40 27.08 –0.15 –0.16 – –4.7 –4.4

12 26.31 26.29 27.05 –0.23 –0.25 – 4.7 1.6

1932 01 26.16 26.30 27.02 –0.38 –0.29 – 1.8 1.2

02 26.57 26.70 26.99 –0.15 –0.08 – –3.6 –2.0

03 27.51 27.40 27.01 0.38 0.25 – –2.5 –2.7

04 28.02 27.92 27.04 0.38 0.40 – –2.1 –1.0

05 28.14 28.04 27.06 0.45 0.40 – 2.8 –0.3

06 27.87 27.75 27.06 0.31 0.28 – –4.7 –2.9

07 27.11 27.27 27.06 0.04 0.15 – –5.0 –5.4

08 26.97 26.96 27.08 0.21 0.15 – –6.9 –6.9

09 26.77 26.82 27.06 0.15 0.16 – –8.8 –7.2

10 26.75 26.72 27.03 0.12 0.12 – –4.3 –5.5

11 26.61 26.54 26.99 0.08 –0.02 – –4.7 –2.6

12 26.18 26.33 26.92 –0.36 –0.21 – 3.2 –2.4

1933 01 26.36 26.40 26.86 –0.18 –0.19 – –11.1 –3.5

02 26.68 26.69 26.79 –0.04 –0.09 – 4.9 –0.8

03 27.05 27.14 26.71 –0.08 –0.02 – –2.0 1.1

04 27.78 27.52 26.63 0.14 –0.01 – 3.6 2.8

05 27.46 27.38 26.55 –0.23 –0.26 – 6.0 2.9

06 26.83 26.92 26.47 –0.73 –0.55 – –3.9 0.4 LN start

07 26.56 26.47 26.41 –0.51 –0.65 – 3.5 0.7 LN

08 25.93 26.10 26.34 –0.83 –0.70 – –0.5 1.1 LN

09 25.98 25.88 26.28 –0.64 –0.78 – 2.0 1.8 LN

10 25.63 25.71 26.23 –1.00 –0.90 – 3.6 4.1 LN

11 25.59 25.55 26.21 –0.94 –1.01 – 7.2 6.6 LN

12 25.38 25.50 26.23 –1.16 –1.04 – 8.2 7.5 LN peak (M)

1934 01 25.64 25.64 26.26 –0.90 –0.95 – 6.5 5.3 LN

02 25.89 25.93 26.29 –0.83 –0.85 – 0.1 1.7 LN

03 26.31 26.47 26.33 –0.82 –0.69 – 0.2 1.7 LN end

04 27.35 27.10 26.38 –0.29 –0.43 – 6.1 1.3

05 27.37 27.36 26.45 –0.32 –0.29 – –7.4 0.5

06 27.35 27.22 26.53 –0.21 –0.25 – 10.7 4.2

07 26.80 26.88 26.60 –0.27 –0.24 – 2.9 –1.6

08 26.55 26.53 26.65 –0.21 –0.27 – –22.4 –12.3

09 26.23 26.37 26.71 –0.39 –0.29 – –6.4 –7.9

10 26.48 26.43 26.74 –0.15 –0.17 – 4.2 3.8

11 26.54 26.48 26.74 0.01 –0.08 – 13.1 7.0

12 26.34 26.37 26.74 –0.20 –0.17 – –2.4 3.7
60

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1935 01 26.26 26.36 26.72 –0.28 –0.23 – 6.5 1.5

02 26.57 26.60 26.73 –0.15 –0.18 – –4.6 2.4

03 26.98 27.00 26.77 –0.15 –0.16 – 12.2 5.7

04 27.45 27.30 26.82 –0.19 –0.23 – 2.8 2.8

05 27.32 27.34 26.86 –0.37 –0.30 – –6.6 –3.2

06 27.28 27.12 26.88 –0.28 –0.36 – –2.3 –2.9

07 26.58 26.84 26.94 –0.49 –0.27 – –0.4 –0.3

08 26.93 26.82 27.01 0.17 0.02 – 2.1 2.5

09 26.83 26.90 27.05 0.21 0.24 – 6.3 5.5

10 27.01 26.95 27.09 0.38 0.35 – 7.3 6.2

11 26.94 26.86 27.13 0.41 0.30 – 3.9 2.8

12 26.55 26.84 27.15 0.01 0.30 – –4.0 –1.5

1936 01 27.32 27.11 27.17 0.78 0.53 – –2.0 –1.9

02 27.25 27.27 27.16 0.53 0.49 – 0.6 0.3

03 27.26 27.46 27.14 0.13 0.30 – 1.8 6.7

04 28.06 27.80 27.14 0.42 0.27 – 22.6 12.9

05 27.80 27.75 27.13 0.11 0.10 – 4.4 7.5

06 27.33 27.34 27.14 –0.23 –0.14 – –1.5 1.4

07 26.88 26.91 27.13 –0.19 –0.21 – 4.2 –0.5

08 26.55 26.66 27.08 –0.21 –0.15 – –8.9 –2.8

09 26.65 26.74 27.08 0.03 0.09 – 2.6 –1.0

10 27.12 26.88 27.09 0.49 0.28 – –0.1 –2.9

11 26.62 26.90 27.07 0.09 0.34 – –13.9 –6.8

12 27.22 26.83 27.06 0.68 0.30 – 0.6 –0.8

1937 01 26.27 26.71 27.08 –0.27 0.12 – 9.4 3.6

02 27.06 26.98 27.10 0.34 0.20 – –5.0 1.4

03 27.51 27.52 27.12 0.38 0.36 – 6.2 2.4

04 27.98 27.73 27.11 0.34 0.20 – 2.0 2.5

05 27.44 27.56 27.10 –0.25 –0.08 – –0.3 1.2

06 27.39 27.39 27.09 –0.17 –0.09 – 3.4 0.2

07 27.32 27.18 27.08 0.25 0.06 – –5.6 –1.1

08 26.67 26.90 27.08 –0.09 0.10 – 3.3 0.5

09 26.93 26.79 27.06 0.31 0.14 – 0.8 –1.1

10 26.63 26.77 27.04 0.00 0.16 – –2.5 –1.6

11 26.87 26.79 27.04 0.34 0.24 – –2.0 0.1

12 26.80 26.71 27.02 0.26 0.17 – 6.7 4.7

1938 01 26.37 26.63 26.95 –0.17 0.05 – 7.5 6.3

02 26.99 26.89 26.88 0.27 0.11 – 3.4 2.7

03 27.20 27.31 26.84 0.07 0.16 – –3.6 –0.1

04 27.86 27.61 26.79 0.22 0.09 – 3.6 4.2

05 27.53 27.43 26.73 –0.16 –0.22 – 13.1 12.0

06 26.80 26.84 26.64 –0.76 –0.63 – 18.0 16.9

07 26.24 26.34 26.58 –0.83 –0.78 – 18.5 17.0

08 26.07 26.21 26.52 –0.69 –0.59 – 13.0 13.0

09 26.47 26.25 26.43 –0.15 –0.41 – 7.5 10.2

10 25.98 26.09 26.39 –0.65 –0.51 – 12.8 8.8 LN start

11 25.93 25.91 26.37 –0.60 –0.65 – 1.9 7.6 LN

12 25.79 25.86 26.42 –0.75 –0.68 – 13.8 11.6 LN
61

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1939 01 25.91 25.86 26.51 –0.63 –0.73 – 17.0 13.9 LN

02 25.81 25.99 26.59 –0.91 –0.79 – 7.7 11.0 LN peak (W)

03 26.41 26.53 26.66 –0.72 –0.62 – 11.6 10.1 LN end

04 27.50 27.26 26.70 –0.14 –0.27 – 9.4 7.3

05 27.61 27.62 26.76 –0.08 –0.03 – –1.1 1.4

06 27.74 27.64 26.84 0.18 0.17 – –1.5 1.0

07 27.48 27.41 26.95 0.41 0.30 – 8.1 3.6

08 26.94 27.14 27.12 0.18 0.34 – –0.5 –4.6

09 27.19 26.90 27.31 0.57 0.24 – –9.4 –8.5

10 26.27 26.68 27.44 –0.36 0.08 – –14.7 –11.7

11 26.98 26.72 27.51 0.45 0.16 – –8.0 –9.8

12 26.64 27.01 27.55 0.10 0.42 – –8.6 –6.3

1940 01 27.76 27.58 27.57 1.22 0.99 – –0.1 –3.2 EN start

02 28.14 28.12 27.60 1.42 1.34 – –4.1 –4.7 EN peak 1 (M)

03 28.44 28.40 27.61 1.31 1.24 – –10.6 –8.7 EN

04 28.57 28.45 27.63 0.93 0.92 – –9.6 –11.1 EN

05 28.21 28.31 27.67 0.52 0.66 – –14.5 –14.5 EN

06 28.24 28.03 27.75 0.68 0.56 – –19.3 –17.1 EN

07 27.43 27.68 27.81 0.36 0.57 – –15.4 –17.2 EN peak 2 (W)

08 27.63 27.37 27.82 0.87 0.57 – –18.5 –18.0 EN peak 2 (W) end

09 26.80 27.07 27.82 0.18 0.42 – –19.6 –19.0

10 27.06 27.07 27.86 0.43 0.47 – –18.4 –15.8

11 27.35 27.44 27.92 0.82 0.88 – –6.7 –15.3 EN start

12 27.98 27.82 27.97 1.44 1.28 – –29.4 –18.8 EN

1941 01 27.95 28.00 28.01 1.41 1.41 – –9.7 –16.1 EN

02 28.11 28.21 28.03 1.39 1.43 – –15.4 –12.8 EN

03 28.67 28.65 28.06 1.54 1.49 – –10.6 –12.0 EN

04 29.13 29.03 28.11 1.49 1.50 – –11.2 –9.9 EN peak 1 (S)

05 29.18 29.02 28.16 1.49 1.37 – –6.6 –9.7 EN

06 28.57 28.57 28.18 1.01 1.10 – –14.4 –14.0 EN

07 27.95 28.03 28.14 0.88 0.92 – –20.6 –18.7 EN

08 27.66 27.68 28.07 0.90 0.87 – –19.1 –16.8 EN

09 27.43 27.56 27.99 0.81 0.90 – –8.2 –13.9 EN

10 27.72 27.68 27.91 1.09 1.07 – –20.2 –14.5 EN

11 27.83 27.81 27.82 1.30 1.25 – –9.3 –11.9 EN peak 2 (M)

12 27.86 27.69 27.70 1.32 1.15 – –8.6 –9.9 EN

1942 01 27.19 27.38 27.59 0.65 0.80 – –13.0 –9.6 EN

02 27.29 27.32 27.46 0.57 0.54 – –3.6 –6.5 EN

03 27.51 27.66 27.31 0.38 0.51 – –5.8 –5.2 EN end

04 28.34 27.99 27.14 0.70 0.46 – –5.5 –2.9

05 27.76 27.76 26.93 0.07 0.11 – 5.2 3.3

06 27.17 27.19 26.72 –0.39 –0.28 – 8.3 5.1

07 26.67 26.61 26.54 –0.40 –0.51 – –1.0 2.6 LN start

08 25.92 26.02 26.39 –0.84 –0.78 – 4.0 3.9 LN

09 25.58 25.62 26.26 –1.04 –1.04 – 8.7 7.5 LN

10 25.41 25.39 26.16 –1.22 –1.22 – 8.5 5.4 LN

11 25.15 25.27 26.10 –1.38 –1.29 – –4.0 3.6 LN peak (M)

12 25.35 25.31 26.10 –1.19 –1.23 – 13.8 8.3 LN
62

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1943 01 25.38 25.42 26.14 –1.16 –1.16 – 9.4 10.8 LN

02 25.58 25.68 26.20 –1.14 –1.10 – 10.5 8.6 LN

03 26.16 26.27 26.28 –0.97 –0.89 – 4.0 8.0 LN

04 27.17 27.00 26.36 –0.47 –0.52 – 13.5 8.5 LN end

05 27.51 27.44 26.44 –0.18 –0.20 – 2.8 2.8

06 27.58 27.45 26.51 0.02 –0.02 – –7.9 –2.5

07 27.13 27.19 26.58 0.06 0.08 – 2.9 1.4

08 26.93 26.88 26.67 0.17 0.08 – 7.8 6.1

09 26.52 26.57 26.76 –0.10 –0.09 – 5.7 7.1

10 26.29 26.32 26.83 –0.34 –0.29 – 9.1 7.0

11 26.16 26.20 26.88 –0.37 –0.36 – 3.9 2.1

12 26.17 26.16 26.90 –0.37 –0.38 – –8.6 –5.4

1944 01 26.15 26.35 26.92 –0.39 –0.24 – –8.2 –5.3

02 26.92 26.76 26.92 0.20 –0.02 – 3.9 1.3

03 27.05 27.23 26.92 –0.08 0.07 – 5.6 2.4

04 27.88 27.70 26.92 0.24 0.18 – –5.5 –1.6

05 28.00 27.90 26.94 0.31 0.26 – –1.1 –2.9

06 27.72 27.69 26.95 0.16 0.22 – –3.9 –4.5

07 27.30 27.30 26.96 0.23 0.19 – –8.9 –4.6

08 26.88 26.88 26.94 0.12 0.07 – 3.3 0.1

09 26.44 26.57 26.89 –0.18 –0.09 – 2.6 0.0

10 26.51 26.44 26.83 –0.12 –0.16 – –8.6 –5.3

11 26.31 26.37 26.77 –0.22 –0.19 – –6.7 –4.5

12 26.33 26.30 26.71 –0.21 –0.24 – 4.2 1.7

1945 01 26.22 26.27 26.66 –0.32 –0.32 – 5.1 5.2

02 26.29 26.32 26.60 –0.43 –0.46 – 6.3 7.7

03 26.47 26.56 26.54 –0.66 –0.60 – 13.2 6.4

04 27.01 26.98 26.49 –0.63 –0.55 – –7.1 –0.3

05 27.41 27.23 26.46 –0.28 –0.42 – –0.3 0.2

06 27.09 27.05 26.45 –0.47 –0.42 – 8.3 5.0

07 26.62 26.59 26.43 –0.45 –0.53 – 3.5 6.8

08 26.03 26.15 26.44 –0.73 –0.65 – 11.7 8.9

09 25.93 25.94 26.47 –0.69 –0.72 – 8.7 7.9

10 25.87 25.96 26.50 –0.76 –0.63 – 2.4 2.5

11 26.23 26.10 26.51 –0.30 –0.46 – –3.4 0.6

12 26.05 26.12 26.54 –0.49 –0.42 – 6.7 1.9

1946 01 26.14 26.22 26.60 –0.40 –0.37 – –2.5 1.5

02 26.53 26.53 26.64 –0.19 –0.25 – 4.4 1.1

03 26.90 26.91 26.68 –0.23 –0.25 – –2.0 –2.3

04 27.29 27.24 26.74 –0.35 –0.29 – –9.6 –8.2

05 27.47 27.52 26.79 –0.22 –0.13 – –11.4 –10.5

06 27.83 27.60 26.82 0.27 0.13 – –9.6 –10.2

07 27.26 27.18 26.88 0.19 0.06 – –10.2 –8.6

08 26.36 26.64 26.92 –0.40 –0.17 – –4.4 –8.8

09 26.56 26.55 26.95 –0.06 –0.11 – –16.0 –12.2

10 26.73 26.37 26.99 0.10 0.02 – –12.3 –10.5

11 26.47 26.57 27.00 –0.06 0.01 – –1.4 –5.2

12 26.61 26.69 27.00 0.07 0.13 – –5.5 –4.3
63

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1947 01 26.97 26.80 26.97 0.43 0.21 – –4.9 –4.9

02 26.63 26.94 26.96 –0.09 0.17 – –4.1 –0.4

03 27.54 27.35 26.93 0.41 0.20 – 11.6 3.6

04 27.70 27.57 26.86 0.06 0.04 – –4.6 –2.8

05 27.32 27.52 26.81 –0.37 –0.12 – –13.7 –7.4

06 27.75 27.41 26.79 0.19 –0.06 – 2.6 0.2

07 26.83 26.98 26.78 –0.24 –0.14 – 9.4 7.2

08 26.51 26.39 26.79 –0.25 –0.42 – 7.2 8.9

09 25.70 25.96 26.83 –0.92 –0.70 – 11.7 7.2

10 25.92 25.87 26.85 –0.71 –0.74 – –1.9 4.3

11 25.93 26.14 26.90 –0.60 –0.42 – 9.2 5.4

12 26.77 26.53 26.94 0.23 –0.01 – 5.2 4.2

1948 01 26.63 26.79 26.95 0.09 0.21 – –3.0 0.5

02 27.13 27.20 26.98 0.41 0.42 – –2.7 –3.1

03 27.89 27.73 27.08 0.76 0.58 – –4.1 –2.0

04 28.02 28.03 27.09 0.38 0.50 – 2.8 1.3

05 28.17 28.03 27.11 0.48 0.38 – 3.6 1.3

06 27.75 27.71 27.13 0.19 0.24 – –4.7 –1.2

07 27.16 27.23 27.12 0.09 0.12 – 0.9 –1.8

08 26.85 26.90 27.09 0.09 0.10 – –4.4 –3.9

09 26.73 26.59 27.04 0.11 –0.07 – –7.6 –3.4

10 26.06 26.30 26.99 –0.57 –0.30 – 6.1 2.3

11 26.35 26.43 26.97 –0.18 –0.13 – 4.6 2.5

12 26.96 26.60 26.92 0.42 0.06 – –5.5 –3.4

1949 01 26.12 26.56 26.88 –0.42 –0.03 – –7.3 –4.5

02 27.02 26.72 26.85 0.30 –0.06 – 2.0 0.6

03 26.70 27.10 26.81 –0.43 –0.06 – 5.6 3.6

04 27.96 27.60 26.78 0.32 0.08 – 1.2 0.6

05 27.79 27.63 26.74 0.10 –0.02 – –5.8 –5.6

06 26.97 27.14 26.63 –0.59 –0.33 – –12.0 –7.9

07 26.84 26.80 26.54 –0.23 –0.31 – –1.7 –5.0

08 26.56 26.52 26.44 –0.20 –0.29 – –4.4 –2.1

09 26.10 26.19 26.35 –0.52 –0.47 – 2.0 1.3

10 26.01 25.86 26.28 –0.62 –0.74 – 5.4 1.7 LN start

11 25.33 25.52 26.18 –1.20 –1.04 – –6.0 0.3 LN

12 25.39 25.41 26.13 –1.15 –1.13 – 7.7 3.6 LN

1950 01 25.53 25.43 26.09 –1.01 –1.16 –1.7b 5.1 8.9 LN

02 25.26 25.56 26.05 –1.46 –1.22 –1.5 17.6 14.5 LN peak 1 (M)

03 26.18 26.12 26.02 –0.95 –1.04 –1.3 17.6 17.4 LN

04 26.86 26.62 25.99 –0.78 –0.91 –1.4p2 16.8 14.7 LN

05 26.56 26.70 25.99 –1.13 –0.95 –1.3 7.6 14.7 LN peak 2 (W)

06 26.82 26.59 25.99 –0.74 –0.89 –1.1 26.9 20.6 LN

07 26.14 26.34 25.99 –0.93 –0.78 –0.8 21.1 20.4 LN

08 26.24 26.07 26.02 –0.52 –0.74 –0.8 12.3 13.2 LN

09 25.65 25.86 26.07 –0.97 –0.80 –0.8 6.9 10.8 LN

10 25.90 25.68 26.11 –0.73 –0.92 –0.9 17.1 13.4 LN

11 25.27 25.50 26.19 –1.26 –1.06 –0.9 12.5 16.3 LN

12 25.55 25.46 26.27 –0.99 –1.08 –1.0p3 23.0 18.8 LN peak 3 (M)
64

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1951 01 25.45 25.62 26.38 –1.09 –0.97 –1.0p3 16.5 16.4 LN

02 26.02 25.99 26.51 –0.70 –0.79 –0.9 9.6 8.6 LN

03 26.48 26.65 26.65 –0.65 –0.51 –0.6e –1.4 1.4 LN end

04 27.60 27.36 26.79 –0.04 –0.16 –0.3 –1.3 –2.7

05 27.77 27.69 26.95 0.08 0.04 –0.2 –6.6 –2.4

06 27.60 27.71 27.11 0.04 0.24 0.2 5.0 –1.2

07 27.88 27.78 27.25 0.81 0.67 0.4 –8.2 –3.0 EN start

08 27.77 27.71 27.36 1.01 0.91 0.7s –0.5 –4.1 EN peak (W)

09 27.42 27.53 27.43 0.80 0.88 0.7 –7.0 –5.6 EN

10 27.52 27.48 27.49 0.89 0.87 0.8p –8.0 –6.6 EN

11 27.44 27.43 27.50 0.91 0.87 0.7 –3.4 –4.5 EN

12 27.30 27.25 27.46 0.76 0.72 0.6e –3.0 –4.7 EN end

1952 01 26.97 27.06 27.39 0.43 0.42 0.3 –9.2 –7.3

02 27.00 27.07 27.28 0.28 0.29 0.1 –7.9 –6.2

03 27.30 27.45 27.18 0.17 0.29 0.1 0.2 –4.1

04 28.18 27.79 27.11 0.54 0.26 0.2 –8.8 –2.9

05 27.48 27.54 27.03 –0.21 –0.10 0.1 6.0 2.7

06 27.03 27.04 26.93 –0.53 –0.43 –0.1 7.4 6.1

07 26.63 26.69 26.87 –0.44 –0.43 –0.3 3.5 2.7

08 26.45 26.48 26.87 –0.31 –0.32 –0.3 –3.7 –1.8

09 26.40 26.49 26.88 –0.22 –0.17 –0.2 –3.4 –2.2

10 26.70 26.53 26.90 0.07 –0.07 –0.2 1.8 –0.1

11 26.33 26.35 26.95 –0.20 –0.16 –0.1 –0.7 –3.1

12 26.04 26.35 27.02 –0.50 –0.20 0.0 –12.6 –5.9

1953 01 26.94 26.73 27.10 0.40 0.15 0.2 2.2 –3.6

02 27.00 27.11 27.15 0.28 0.33 0.4 –6.0 –3.9

03 27.48 27.63 27.22 0.35 0.47 0.5 –5.8 –4.5

04 28.54 28.19 27.26 0.90 0.67 0.5 –0.5 –9.7

05 28.21 28.27 27.30 0.52 0.62 0.5 –31.9 –16.7

06 28.10 27.96 27.35 0.54 0.49 0.5 –2.3 –9.4

07 27.42 27.46 27.38 0.35 0.35 0.4 –1.0 –5.4

08 26.91 27.17 27.38 0.15 0.36 0.4 –17.2 –12.1

09 27.42 27.15 27.37 0.80 0.49 0.4 –13.0 –10.8

10 26.84 27.02 27.32 0.21 0.41 0.4 –0.1 –3.8

11 26.96 26.88 27.24 0.43 0.32 0.4 –2.0 –2.0

12 26.74 26.85 27.15 0.20 0.32 0.4 –4.0 –1.0

1954 01 26.97 26.89 27.05 0.43 0.33 0.5 6.0 1.1

02 26.98 27.05 26.95 0.26 0.27 0.3 –3.6 –0.5

03 27.27 27.24 26.85 0.14 0.09 –0.1 –0.9 0.4

04 27.45 27.38 26.72 –0.19 –0.15 –0.5s 6.9 4.3

05 27.34 27.25 26.62 –0.35 –0.39 –0.7 4.4 3.6

06 26.88 26.83 26.52 –0.68 –0.65 –0.7 –1.5 1.4 LN start

07 26.20 26.27 26.43 –0.87 –0.85 –0.8 4.2 4.3 LN

08 25.80 25.88 26.35 –0.96 –0.92 –1.0 10.4 7.4 LN peak 1 (W)

09 25.72 25.77 26.27 –0.90 –0.89 –1.2p1 4.5 5.3 LN

10 25.82 25.71 26.21 –0.81 –0.89 –1.1 1.8 3.0 LN

11 25.49 25.65 26.16 –1.04 –0.91 –1.1 3.9 5.6 LN peak 2 (W)

12 25.79 25.75 26.11 –0.75 –0.79 –1.1 12.8 6.0 LN
65

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1955 01 25.92 25.90 26.08 –0.62 –0.68 –1.0 –5.4 4.3 LN

02 25.98 26.09 26.08 –0.72 –0.68 –0.9 15.2 7.0 LN

03 26.46 26.42 26.07 –0.67 –0.72 –0.9 2.9 4.5 LN

04 26.82 26.69 26.03 –0.82 –0.84 –1.0 –3.0 2.5 LN

05 26.64 26.65 25.97 –1.05 –1.00 –1.0 13.1 9.9 LN

06 26.49 26.38 25.91 –1.07 –1.09 –1.0 16.4 16.3 LN peak 3 (M)

07 25.91 26.07 25.86 –1.16 –1.05 –1.0 19.2 17.4 LN

08 25.96 25.81 25.82 –0.80 –0.99 –1.0 14.9 15.8 LN

09 25.42 25.49 25.81 –1.20 –1.17 –1.4 14.1 14.6 LN

10 25.14 25.11 25.81 –1.49 –1.49 –1.8 15.2 14.9 LN

11 24.75 24.93 25.85 –1.78 –1.56 –2.0p2 15.1 13.7 LN peak 4 (S)

12 25.07 25.06 25.89 –1.47 –1.48 –1.9 9.3 11.3 LN

1956 01 25.35 25.39 25.92 –1.19 –1.20 –1.3 11.3 11.1 LN

02 25.79 25.81 25.94 –0.93 –0.97 –0.9 12.4 11.4 LN

03 26.32 26.36 25.96 –0.81 –0.80 –0.7 9.4 10.6 LN

04 26.99 26.90 26.01 –0.65 –0.63 –0.6 11.1 12.4 LN

05 27.28 27.10 26.09 –0.41 –0.55 –0.6 17.9 14.8 LN

06 26.85 26.82 26.17 –0.71 –0.66 –0.6 12.3 13.8 LN

07 26.28 26.37 26.23 –0.79 –0.75 –0.7 12.6 12.1 LN peak 5 (W)

08 26.06 26.06 26.29 –0.70 –0.74 –0.8 11.0 8.7 LN

09 25.84 25.95 26.36 –0.78 –0.71 –0.8 0.2 7.4 LN

10 26.04 25.89 26.46 –0.59 –0.71 –0.9p3 18.3 9.7 LN

11 25.64 25.83 26.55 –0.89 –0.73 –0.9p3 1.9 8.1 LN peak 6(W)

12 26.01 25.92 26.65 –0.53 –0.62 –0.8p3 10.3 7.0 LN end

1957 01 26.02 26.14 26.77 –0.52 –0.44 –0.5e 5.6 4.8

02 26.52 26.60 26.91 –0.20 –0.18 –0.1 –2.2 0.1

03 27.34 27.35 27.04 –0.21 –0.02 0.3 –0.9 –0.7

04 28.19 28.01 27.16 0.55 0.38 0.6s 1.2 –2.7

05 28.31 28.26 27.30 0.62 0.61 0.7 –12.2 –6.4 EN start

06 28.22 28.17 27.46 0.66 0.70 0.9p1 –2.3 –4.0 EN

07 27.91 27.93 27.62 0.84 0.81 0.9p1 0.9 –2.5 EN

08 27.66 27.63 27.78 0.90 0.83 0.9p1 –9.5 –7.2 EN peak 1 (W)

09 27.28 27.43 27.89 0.66 0.77 0.9p1 –10.6 –8.0 EN

10 27.48 27.50 27.92 0.85 0.89 1.0 –1.3 –6.3 EN

11 27.74 27.68 27.91 1.21 1.12 1.2 –11.9 –7.2 EN

12 27.76 27.85 27.89 1.22 1.31 1.5 –3.5 –8.9 EN

1958 01 28.12 28.04 27.86 1.58 1.46 1.7p2 –16.8 –11.0 EN peak 2 (M)

02 28.16 28.17 27.81 1.44 1.40 1.5 –6.9 –8.0 EN

03 28.25 28.19 27.75 1.12 1.03 1.2 –1.4 –2.1 EN

04 28.08 28.15 27.68 0.44 0.63 0.8 1.2 –1.8 EN end

05 28.19 28.11 27.61 0.50 0.47 0.6 –8.2 –3.8

06 27.99 27.86 27.53 0.43 0.39 0.5e 0.2 –1.4

07 27.26 27.41 27.45 0.19 0.29 0.3 2.2 3.1

08 27.12 26.99 27.36 0.36 0.18 0.1 7.8 3.6

09 26.44 26.68 27.29 –0.18 0.02 0.0 –3.4 –0.2

10 26.70 26.64 27.26 0.07 0.04 0.0 –1.9 –3.0

11 26.71 26.75 27.25 0.18 0.20 0.2 –4.7 –4.5

12 26.89 26.88 27.21 0.35 0.34 0.4 –6.5 –6.6
66

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1959 01 27.01 27.04 27.17 0.47 0.46 0.4 –8.7 –9.5

02 27.26 27.26 27.13 0.54 0.49 0.5 –14.0 –7.1

03 27.52 27.59 27.09 0.39 0.43 0.4 8.4 1.6

04 28.04 27.86 27.09 0.40 0.34 0.2 3.6 4.6

05 27.85 27.78 27.08 0.16 0.13 0.0 2.8 0.7

06 27.36 27.38 27.06 –0.20 –0.09 –0.2 –6.3 –3.7

07 26.95 26.93 27.03 –0.12 –0.18 –0.4 –5.0 –5.3

08 26.47 26.53 26.98 –0.29 –0.28 –0.5 –5.0 –3.7

09 26.22 26.44 26.93 –0.40 –0.22 –0.4 0.2 –0.1

10 26.84 26.60 26.91 0.21 –0.01 –0.3 4.2 4.9

11 26.48 26.59 26.90 –0.05 0.03 –0.2 11.1 8.7

12 26.54 26.54 26.91 0.00 0.00 –0.2 8.2 7.0

1960 01 26.60 26.57 26.92 0.06 –0.02 –0.3 0.3 1.7

02 26.52 26.70 26.93 –0.20 –0.08 –0.3 –2.2 0.4

03 27.17 27.16 26.97 0.04 0.01 –0.3 5.6 4.2

04 27.78 27.66 26.99 0.14 0.14 –0.2 7.8 6.6

05 27.92 27.78 26.97 0.23 0.13 –0.2 5.2 4.0

06 27.48 27.47 26.97 –0.08 –0.01 –0.2 –2.3 1.4

07 26.98 27.08 26.96 –0.09 –0.04 –0.1 4.8 3.5

08 26.87 26.88 26.97 0.11 0.08 0.0 6.6 6.2

09 26.79 26.78 26.98 0.17 0.12 –0.1 6.9 4.9

10 26.67 26.60 26.98 0.04 0.00 –0.2 –0.7 3.2

11 26.27 26.45 26.99 –0.26 –0.11 –0.2 7.2 5.1

12 26.60 26.48 27.00 0.06 –0.06 –0.2 6.7 4.5

1961 01 26.43 26.57 27.01 –0.11 –0.02 –0.2 –2.5 2.0

02 26.80 26.80 26.99 0.08 0.02 –0.2 6.3 –2.7

03 27.16 27.26 26.96 0.03 0.10 –0.2 –20.9 –6.5

04 27.90 27.71 26.91 0.26 0.18 –0.1 9.4 –0.2

05 27.86 27.85 26.89 0.17 0.21 0.1 1.3 2.2

06 27.79 27.59 26.89 0.23 0.12 0.2 –3.1 –0.7

07 26.90 27.05 26.87 –0.17 –0.06 0.0 2.2 0.4

08 26.62 26.59 26.86 –0.14 –0.21 –0.3 0.1 0.8

09 26.23 26.28 26.83 –0.39 –0.38 –0.6 0.8 –0.8

10 26.02 26.18 26.80 –0.61 –0.42 –0.6 –5.0 –0.5

11 26.46 26.31 26.77 –0.07 –0.25 –0.5 7.2 5.8

12 26.30 26.35 26.74 –0.24 –0.19 –0.4 13.8 13.0

1962 01 26.33 26.39 26.72 –0.21 –0.20 –0.4 17.0 13.3

02 26.60 26.60 26.73 –0.12 –0.18 –0.4 5.3 6.6

03 26.85 26.94 26.73 –0.28 –0.22 –0.4 –1.4 0.9

04 27.45 27.30 26.75 –0.19 –0.23 –0.5 1.2 3.3

05 27.45 27.46 26.75 –0.24 –0.19 –0.4 12.3 7.7

06 27.47 27.33 26.74 –0.09 –0.14 –0.4 5.0 5.5

07 26.92 27.01 26.72 –0.15 –0.10 –0.3 –0.4 2.2

08 26.74 26.65 26.72 –0.02 –0.16 –0.3 4.6 3.5

09 26.19 26.38 26.73 –0.43 –0.28 –0.5 5.1 6.3

10 26.41 26.31 26.75 –0.22 –0.30 –0.6 10.3 7.7

11 26.22 26.24 26.78 –0.31 –0.32 –0.7 5.2 5.3

12 26.09 26.17 26.81 –0.45 –0.37 –0.7 0.6 4.0
67

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1963 01 26.26 26.28 26.87 –0.28 –0.31 –0.6 9.4 5.6

02 26.50 26.62 26.96 –0.22 –0.16 –0.3 3.0 5.7

03 27.20 27.15 27.05 0.07 0.00 0.0 7.3 5.9

04 27.71 27.62 27.15 0.07 0.10 0.1 6.1 5.6

05 27.86 27.81 27.25 0.17 0.17 0.1 2.8 0.5

06 27.81 27.86 27.36 0.25 0.39 0.3 –9.6 –4.4

07 27.95 27.87 27.47 0.88 0.76 0.6s –1.0 –3.5 EN start

08 27.78 27.73 27.55 1.02 0.93 0.8 –2.4 –2.8 EN peak 1 (W)

09 27.40 27.54 27.58 0.78 0.88 0.9 –5.2 –6.4 EN

10 27.57 27.49 27.55 0.94 0.88 0.9 –12.9 –10.1 EN

11 27.40 27.50 27.50 0.87 0.94 1.0p –9.3 –10.8 EN

12 27.63 27.50 27.43 1.09 0.96 1.0p –11.6 –9.1 EN peak 2 (W)

1964 01 27.33 27.40 27.33 0.79 0.82 0.8e –4.0 –5.0 EN end

02 27.31 27.26 27.20 0.59 0.49 0.4 –0.3 1.0

03 27.10 27.19 27.07 –0.03 0.03 –0.1 8.4 7.5

04 27.24 27.18 26.93 –0.40 –0.35 –0.5s 13.5 9.6

05 27.13 27.08 26.77 –0.56 –0.57 –0.8 2.8 6.6 LN start

06 26.81 26.83 26.61 –0.75 –0.64 –0.8 7.4 6.1 LN peak 1 (W)

07 26.58 26.52 26.46 –0.49 –0.60 –0.9 6.8 8.8 LN

08 26.11 26.16 26.37 –0.65 –0.65 –1.0 14.3 12.4 LN

09 25.82 25.87 26.33 –0.80 –0.79 –1.1 14.1 13.8 LN

10 25.73 25.71 26.34 –0.90 –0.90 –1.2p 12.8 10.6 LN

11 25.55 25.59 26.39 –0.98 –0.97 –1.2p 2.6 3.8 LN peak 2 (W)

12 25.52 25.65 26.49 –1.02 –0.89 –1.0 –3.0 –1.9 LN

1965 01 26.01 25.99 26.60 –0.53 –0.60 –0.8e –4.0 –2.4 LN end

02 26.41 26.44 26.75 –0.31 –0.34 –0.4 1.6 0.5

03 26.92 26.98 26.92 –0.21 –0.17 –0.2 2.9 –1.4

04 27.68 27.58 27.12 0.04 0.06 0.0 –12.9 –5.8

05 28.05 27.98 27.34 0.36 0.34 0.3 –0.3 –6.6

06 28.14 28.09 27.56 0.58 0.62 0.6s –12.8 –12.1 EN start

07 28.03 28.08 27.73 0.96 0.97 1.0 –22.6 –17.4 EN

08 28.12 28.07 27.85 1.36 1.27 1.2 –11.4 –14.9 EN

09 28.01 28.12 27.95 1.39 1.46 1.4 –14.2 –12.7 EN

10 28.34 28.22 28.03 1.71 1.62 1.5 –11.1 –13.6 EN

11 28.20 28.20 28.04 1.67 1.64 1.6p –17.9 –11.3 EN peak (S)

12 28.04 28.00 28.02 1.50 1.46 1.5 1.6 –6.7 EN

1966 01 27.71 27.76 27.98 1.17 1.18 1.2 –12.0 –6.6 EN

02 27.59 27.74 27.90 0.87 0.97 1.0 –4.1 –8.5 EN

03 28.08 28.02 27.79 0.95 0.86 0.8 –13.9 –9.8 EN

04 28.31 28.13 27.67 0.67 0.60 0.5e –7.1 –9.3 EN end

05 27.81 27.94 27.52 0.12 0.29 0.2 –9.0 –6.0

06 27.82 27.73 27.37 0.26 0.26 0.2 1.0 –2.0

07 27.45 27.37 27.22 0.38 0.26 0.2 –1.0 0.8

08 26.77 26.92 27.10 0.01 0.12 0.0 4.0 1.2

09 26.70 26.72 26.98 0.08 0.06 –0.2 –2.2 –2.7

10 26.69 26.59 26.89 0.06 0.01 –0.2 –2.5 –1.8

11 26.28 26.39 26.83 –0.25 –0.17 –0.3 –0.1 –1.7

12 26.32 26.24 26.82 –0.22 –0.30 –0.3 –4.0 1.6
68

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1967 01 26.02 26.14 26.79 –0.52 –0.45 –0.4 14.6 9.5

02 26.20 26.30 26.77 –0.52 –0.48 –0.4 12.9 12.1

03 26.79 26.76 26.74 –0.34 –0.40 –0.6 7.8 6.4

04 27.24 27.23 26.70 –0.40 –0.30 –0.5 –3.0 1.3

05 27.63 27.52 26.69 –0.06 –0.13 –0.3 –3.5 –0.9

06 27.56 27.47 26.69 0.00 0.00 0.0 6.6 2.8

07 27.12 27.09 26.68 0.05 –0.02 0.0 1.6 3.9

08 26.57 26.61 26.67 –0.19 –0.20 –0.2 5.9 4.6

09 26.17 26.32 26.65 –0.45 –0.34 –0.4 5.1 4.0

10 26.35 26.30 26.64 –0.28 –0.31 –0.5 –0.1 0.2

11 26.32 26.31 26.64 –0.21 –0.25 –0.4 –4.0 –3.4

12 26.24 26.20 26.64 –0.30 –0.34 –0.5 –5.5 –2.7

1968 01 25.98 26.06 26.67 –0.56 –0.53 –0.7 4.1 3.1

02 26.02 26.13 26.72 –0.70 –0.65 –0.9 9.6 5.1

03 26.50 26.58 26.77 –0.63 –0.58 –0.8 –3.0 0.2

04 27.30 27.13 26.83 –0.34 –0.39 –0.7 –3.0 1.4

05 27.43 27.51 26.90 –0.26 –0.14 –0.3 14.7 9.7

06 27.87 27.68 26.99 0.31 0.21 0.0 12.3 11.7

07 27.54 27.54 27.10 0.47 0.42 0.3 7.4 6.8

08 27.20 27.19 27.24 0.44 0.38 0.4 0.1 1.2

09 26.80 26.96 27.37 0.18 0.31 0.3 –2.8 –1.9

10 27.05 27.08 27.46 0.42 0.48 0.4 –1.9 –2.5

11 27.42 27.31 27.53 0.89 0.75 0.7s –3.4 –1.7 EN start

12 27.35 27.40 27.56 0.81 0.86 0.9 2.1 –3.2 EN

1969 01 27.48 27.53 27.56 0.94 0.94 1.0p –13.5 –8.0 EN

02 27.79 27.73 27.56 1.07 0.95 1.0p –6.9 –6.4 EN peak (W)

03 27.86 27.79 27.58 0.73 0.75 0.9 1.8 –3.0 EN

04 28.10 28.08 27.61 0.96 0.55 0.7 –8.8 –5.6 EN end

05 28.25 28.14 27.63 0.56 0.49 0.6 –6.6 –5.7

06 27.95 27.87 27.62 0.39 0.40 0.5e –0.6 –3.7

07 27.32 27.50 27.60 0.25 0.38 0.4 –6.9 –4.7

08 27.39 27.33 27.56 0.63 0.53 0.4 –4.4 –6.6 EN start

09 27.22 27.31 27.52 0.60 0.65 0.6s –10.6 –9.3 EN

10 27.39 27.35 27.50 0.76 0.75 0.7 –11.7 –8.5 EN

11 27.40 27.37 27.48 0.87 0.81 0.8p –0.1 –2.1 EN peak (W)

12 27.27 27.27 27.44 0.73 0.73 0.7 3.7 –0.7 EN

1970 01 27.13 27.16 27.37 0.59 0.58 0.5e –10.1 –6.8 EN end

02 27.12 27.22 27.26 0.40 0.45 0.3 –10.7 –7.4

03 27.52 27.53 27.15 0.39 0.37 0.2 1.8 –2.9

04 27.95 27.82 27.04 0.31 0.30 0.1 –4.6 –1.3

05 27.87 27.77 26.92 0.18 0.12 0.0 2.1 2.4

06 27.38 27.22 26.78 –0.18 –0.07 –0.3 9.9 4.1

07 26.25 26.45 26.62 –0.82 –0.67 –0.6s –5.6 0.7 LN start

08 25.92 26.02 26.47 –0.84 –0.79 –0.8 4.0 3.8 LN peak 1 (W)

09 25.97 25.99 26.34 –0.65 –0.67 –0.9p1 12.9 10.0 LN

10 26.08 25.99 26.27 –0.55 –0.62 –0.8 10.3 13.3 LN

11 25.81 25.79 26.14 –0.72 –0.77 –0.9 19.7 16.8 LN

12 25.47 25.47 26.09 –1.07 –1.07 –1.1 17.4 14.3 LN
69

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1971 01 25.11 25.29 26.08 –1.43 –1.29 –1.3p2 2.7 9.6 LN peak 2 (M)

02 25.48 25.51 26.11 –1.24 –1.27 –1.3p2 15.7 13.3 LN

03 25.96 26.05 26.12 –1.17 –1.11 –1.1 19.2 19.2 LN

04 26.80 26.65 26.12 –0.84 –0.88 –0.9 22.6 18.4 LN

05 27.04 26.95 26.11 –0.65 –0.70 –0.8 9.2 10.9 LN

06 26.91 26.86 26.12 –0.65 –0.61 –0.8 2.6 4.0 LN

07 26.59 26.58 26.17 –0.48 –0.54 –0.8 1.6 5.2 LN

08 26.22 26.26 26.25 –0.54 –0.55 –0.8 14.9 11.8 LN

09 26.00 26.04 26.34 –0.62 –0.62 –0.8 15.9 16.1 LN

10 25.95 25.93 26.43 –0.68 –0.68 –0.9 17.7 14.6 LN

11 25.80 25.81 26.53 –0.73 –0.75 –1.0p3 7.2 8.6 LN peak 3 (W)

12 25.69 25.80 26.63 –0.85 –0.74 –0.9 2.1 3.8 LN

1972 01 26.00 26.06 26.75 –0.54 –0.53 –0.7e 3.7 4.4 LN end

02 26.55 26.53 26.90 –0.17 –0.25 –0.4 8.2 5.6

03 27.00 27.13 27.06 –0.13 –0.02 0.0 2.4 1.9

04 27.98 27.79 27.25 0.34 0.26 0.2 –5.5 –6.2

05 28.19 28.18 27.47 0.50 0.53 0.5s –16.1 –12.4 EN start

06 28.35 28.24 27.71 0.79 0.77 0.8 –12.0 –14.7 EN

07 28.06 28.16 27.93 0.99 1.05 1.0 –18.6 –14.5 EN

08 28.18 28.09 28.07 1.42 1.29 1.3 –8.9 –12.8 EN

09 27.94 28.14 28.16 1.32 1.48 1.5 –14.8 –12.4 EN

10 28.50 28.37 28.19 1.87 1.77 1.8 –11.1 –10.1 EN

11 28.53 28.59 28.14 2.00 2.03 2.0 –3.4 –7.5 EN peak (VS)

12 28.78 28.57 28.04 2.24 2.03 2.1p –12.1 –7.7 EN peak (VS)

1973 01 28.18 28.25 27.89 1.64 1.66 1.8 –3.0 –7.9 EN

02 27.84 27.92 27.70 1.12 1.15 1.2 –13.5 –7.3 EN

03 27.83 27.80 27.49 0.70 0.65 0.5e 0.8 –3.5 EN end

04 27.70 27.63 27.24 0.06 0.11 –0.1 –2.1 –0.2

05 27.30 27.28 26.94 –0.39 –0.36 –0.6s 2.8 4.0

06 26.83 26.76 26.59 –0.73 –0.71 –0.9 12.3 8.4 LN start

07 26.08 26.16 26.26 –0.99 –0.95 –1.1 6.1 9.2 LN

08 25.66 25.69 26.00 –1.10 –1.12 –1.3 12.3 11.1 LN

09 25.35 25.38 25.81 –1.27 –1.28 –1.4 13.5 12.3 LN

10 25.15 25.06 25.69 –1.48 –1.55 –1.7 9.7 16.1 LN

11 24.58 24.68 25.64 –1.95 –1.88 –2.0 31.6 22.5 LN

12 24.41 24.49 25.64 –2.13 –2.05 –2.1p1 16.9 21.6 LN peak (VS)

1974 01 24.56 24.70 25.66 –1.98 –1.89 –1.9 20.8 18.7 LN

02 25.26 25.23 25.72 –1.46 –1.55 –1.7 16.2 18.4 LN

03 25.82 25.92 25.80 –1.31 –1.37 –1.3 20.3 17.0 LN

04 26.77 26.61 25.88 –0.87 –0.92 –1.1 11.1 13.3 LN

05 27.07 26.98 25.96 –0.62 –0.67 –0.9 10.7 8.8 LN

06 26.99 26.91 26.06 –0.57 –0.56 –0.8 2.6 7.0 LN end

07 26.58 26.68 26.19 –0.49 –0.44 –0.6 12.0 8.3

08 26.56 26.53 26.30 –0.20 –0.28 –0.5 6.6 9.4

09 26.40 26.34 26.39 –0.22 –0.32 –0.5 12.3 9.9

10 25.98 26.02 26.44 –0.65 –0.59 –0.7 8.5 7.0

11 25.70 25.78 26.45 –0.83 –0.78 –0.9p2 –1.4 1.2

12 25.73 25.84 26.42 –0.81 –0.70 –0.7 –0.9 –2.0
70

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1975 01 26.21 26.15 26.37 –0.33 –0.44 –0.6 –4.9 –1.4

02 26.43 26.43 26.31 –0.29 –0.35 –0.6 5.3 4.3

03 26.66 26.73 26.23 –0.47 –0.42 –0.7 11.6 10.7

04 27.18 26.97 26.15 –0.46 –0.55 –0.8 14.4 11.6 LN start

05 26.87 26.84 26.10 –0.82 –0.81 –0.9 6.0 10.5 LN

06 26.43 26.43 26.05 –1.13 –1.04 –1.1 15.5 14.5 LN

07 25.99 26.06 25.96 –1.08 –1.08 –1.2 21.1 19.6 LN

08 25.72 25.69 25.87 –1.04 –1.12 –1.3 20.7 21.3 LN

09 25.31 25.40 25.83 –1.31 –1.26 –1.5 22.5 20.9 LN

10 25.26 25.26 25.84 –1.37 –1.35 –1.6 17.7 17.9 LN

11 25.19 25.15 25.87 –1.34 –1.41 –1.7p3 13.8 16.2 LN

12 24.95 24.97 25.94 –1.59 –1.57 –1.7p3 19.5 16.2 LN peak (S)

1976 01 24.78 25.06 26.05 –1.76 –1.53 –1.6 11.8 14.0 LN

02 25.71 25.70 26.17 –1.01 –1.08 –1.2 12.9 12.7 LN

03 26.58 26.56 26.31 –0.55 –0.60 –0.8 13.2 10.1 LN end

04 27.35 27.16 26.49 –0.29 –0.36 –0.6 1.2 4.4

05 27.37 27.45 26.69 –0.32 –0.20 –0.5e 2.1 1.4

06 27.69 27.53 26.88 0.13 0.06 –0.2 0.2 –2.6

07 27.38 27.41 27.09 0.31 0.29 0.1 –12.8 –9.4

08 27.18 27.27 27.26 0.42 0.46 0.3 –12.1 –12.5

09 27.32 27.35 27.37 0.70 0.70 0.5s –13.0 –8.8 EN start

10 27.59 27.51 27.43 0.96 0.91 0.7 3.0 0.7 EN

11 27.54 27.48 27.45 1.01 0.92 0.8p 9.8 4.9 EN peak (W)

12 27.23 27.36 27.49 0.69 0.82 0.7 –3.0 –0.1 EN

1977 01 27.42 27.35 27.51 0.88 0.76 0.6 –4.0 –0.8 EN

02 27.31 27.42 27.52 0.59 0.65 0.5e 7.7 0.5 EN end

03 27.65 27.53 27.52 0.52 0.38 0.2 –9.5 –5.2

04 27.52 27.63 27.51 –0.12 0.11 0.2 –9.6 –10.0

05 27.84 27.81 27.52 0.15 0.17 0.2 –11.4 –12.5

06 28.05 27.90 27.55 0.49 0.43 0.4 –17.7 –15.4

07 27.67 27.63 27.56 0.60 0.52 0.4 –14.7 –14.8

08 27.13 27.15 27.55 0.37 0.48 0.4 –12.1 –12.1

09 27.19 27.28 27.54 0.57 0.63 0.5s –9.4 –11.0 EN start

10 27.62 27.53 27.52 0.99 0.93 0.6 –12.9 –12.5 EN

11 27.69 27.67 27.49 1.16 1.11 0.7p –14.6 –13.2 EN peak (M)

12 27.67 27.58 27.44 1.13 1.05 0.7p –10.6 –9.7 EN

1978 01 27.30 27.39 27.37 0.76 0.80 0.7pe –3.0 –10.3 EN

02 27.27 27.29 27.29 0.55 0.51 0.4 –24.4 –14.4 EN end

03 27.32 27.33 27.21 0.19 0.17 0.0 –5.8 –11.0

04 27.40 27.37 27.12 –0.24 –0.15 –0.3 –7.9 –1.3

05 27.37 27.34 27.02 –0.32 –0.30 –0.4 16.3 7.6

06 27.23 27.15 26.93 –0.33 –0.33 –0.4 5.8 8.5

07 26.75 26.75 26.86 –0.32 –0.37 –0.4 6.1 4.9

08 26.26 26.36 26.81 –0.50 –0.45 –0.4 1.4 2.4

09 26.15 26.24 26.80 –0.47 –0.42 –0.4 0.8 –0.8

10 26.39 26.36 26.82 –0.24 –0.25 –0.3 –6.2 –3.4

11 26.50 26.51 26.86 –0.03 –0.05 –0.2 –2.0 –2.8

12 26.66 26.61 26.90 0.12 0.08 –0.1 –0.9 –2.0
71

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1979 01 26.63 26.70 26.93 0.09 0.11 –0.1 –4.0 –0.6

02 26.86 26.93 26.97 0.14 0.16 0.0 6.7 1.6

03 27.38 27.39 27.05 0.25 0.24 0.1 –3.0 –1.2

04 27.94 27.76 27.13 0.30 0.23 0.1 –5.5 –2.6

05 27.77 27.80 27.18 0.08 0.16 0.1 3.6 1.9

06 27.72 27.56 27.22 0.16 0.09 –0.1 5.8 1.8

07 27.02 27.21 27.27 –0.05 0.10 0.0 –8.2 –3.9

08 27.09 27.11 27.30 0.33 0.31 0.1 –5.0 –4.2

09 27.23 27.15 27.31 0.61 0.49 0.3 1.4 –1.2

10 27.05 27.08 27.31 0.42 0.48 0.4 –2.5 –2.1

11 27.00 27.08 27.32 0.47 0.53 0.5 –4.7 –4.9

12 27.28 27.17 27.34 0.74 0.64 0.5 –7.5 –4.1

1980 01 27.13 27.16 27.41 0.59 0.57 0.5 3.2 0.0

02 27.09 27.17 27.36 0.37 0.39 0.3 1.1 –0.8

03 27.35 27.44 27.31 0.22 0.29 0.2 –8.5 –7.2

04 27.97 27.82 27.27 0.33 0.30 0.2 –12.9 –9.5

05 28.00 28.01 27.24 0.31 0.36 0.3 –3.5 –6.2

06 28.05 27.84 27.22 0.49 0.37 0.3 –4.7 –3.7

07 27.25 27.30 27.16 0.18 0.19 0.2 –1.7 –1.7

08 26.65 26.80 27.09 –0.11 –0.01 0.0 1.4 –1.0

09 26.63 26.64 27.05 0.01 –0.02 –0.1 –5.2 –2.7

10 26.63 26.66 27.03 0.00 0.06 –0.1 –1.9 –3.1

11 26.75 26.77 27.00 0.22 0.21 0.0 –3.4 –2.4

12 26.94 26.69 26.97 0.40 0.15 –0.1 –0.9 –0.6

1981 01 26.12 26.37 26.93 –0.42 –0.21 –0.3 2.7 0.3

02 26.31 26.50 26.92 –0.41 –0.28 –0.5 –3.2 –5.1

03 27.24 27.10 26.92 0.11 –0.06 –0.5 –16.6 –10.5

04 27.60 27.55 26.92 –0.04 0.03 –0.4 –5.5 –5.0

05 27.76 27.67 26.91 0.07 0.02 –0.3 7.6 5.3

06 27.54 27.41 26.89 –0.02 –0.06 –0.3 11.5 10.0

07 26.79 26.96 26.89 –0.28 –0.16 –0.4 9.4 9.1

08 26.70 26.72 26.92 –0.06 –0.09 –0.4 5.9 7.2

09 26.68 26.69 26.94 0.06 0.03 –0.3 7.5 4.0

10 26.70 26.62 26.95 0.07 0.02 –0.2 –5.0 0.0

11 26.39 26.53 27.00 –0.14 –0.03 –0.1 2.6 1.2

12 26.65 26.56 27.08 0.11 0.02 –0.1 4.7 5.4

1982 01 26.54 26.59 27.17 0.00 0.01 0.0 9.4 6.0

02 26.64 26.77 27.26 –0.08 –0.01 0.1 0.6 3.3

03 27.24 27.28 27.36 0.11 0.13 0.1 2.4 0.4

04 28.01 27.94 27.51 0.37 0.42 0.3 –3.8 –3.4

05 28.51 28.41 27.69 0.82 0.77 0.6s –8.2 –10.1 EN start

06 28.61 28.40 27.88 1.05 0.93 0.7 –20.1 –16.9 EN peak 1 (W)

07 27.86 28.03 28.08 0.79 0.92 0.7 –19.3 –20.6 EN

08 27.80 27.90 28.28 1.04 1.10 1.0 –23.6 –22.0 EN

09 28.14 28.20 28.45 1.52 1.55 1.5 –21.4 –21.7 EN

10 28.73 28.58 28.56 2.10 1.98 1.9 –20.2 –23.2 EN

11 28.72 28.77 28.61 2.19 2.22 2.2 –31.1 –25.9 EN

12 28.92 28.89 28.62 2.38 2.36 2.3p –21.3 –26.1 EN
72

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1983 01 29.01 28.98 28.58 2.47 2.40 2.3p –30.6 –29.0 EN peak 2 (VS)

02 28.98 28.98 28.50 2.26 2.20 2.0 –33.3 –31.3 EN

03 28.95 28.94 28.38 1.82 1.79 1.5 –28.0 –26.6 EN

04 28.89 28.93 28.18 1.25 1.41 1.2 –17.0 –14.0 EN

05 28.99 28.80 27.92 1.30 1.15 1.0 6.0 –2.0 EN

06 28.31 28.18 27.65 0.75 0.71 0.6e –3.1 –2.0 EN end

07 27.11 27.32 27.37 0.04 0.21 0.2 –7.6 –4.6

08 26.75 26.72 27.15 –0.01 –0.09 –0.2 0.1 0.6

09 26.26 26.24 26.92 –0.36 –0.42 –0.6 9.9 6.0

10 25.70 25.80 26.76 –0.93 –0.81 –0.8 4.2 4.4 LN start

11 25.52 25.60 26.61 –1.01 –0.96 –0.9 –0.7 0.7 LN peak (W)

12 25.64 25.65 26.48 –0.90 –0.89 –0.7 0.1 0.2 LN

1984 01 25.78 25.86 26.40 –0.76 –0.73 –0.4 1.3 2.1 LN

02 26.23 26.26 26.38 –0.49 –0.52 –0.2 5.8 1.8 LN end

03 26.78 26.74 26.37 –0.35 –0.42 –0.2 –5.8 –1.0

04 27.17 27.09 26.39 –0.47 –0.44 –0.3 2.0 –0.5

05 27.22 27.10 26.39 –0.47 –0.55 –0.5 –0.3 –1.8

06 26.79 26.91 26.37 –0.77 –0.57 –0.4 –8.7 –3.9

07 26.82 26.73 26.34 –0.25 –0.39 –0.3 2.2 –0.4

08 26.47 26.54 26.32 –0.29 –0.26 –0.2 2.7 2.4

09 26.40 26.29 26.28 –0.22 –0.37 –0.3 2.0 0.4

10 25.90 25.92 26.25 –0.73 –0.68 –0.6s –5.0 –1.0 LN start

11 25.48 25.48 26.22 –1.05 –1.08 –0.9 3.9 0.4 LN

12 25.05 25.32 26.22 –1.49 –1.22 –1.1p –1.4 –0.6 LN peak (M)

1985 01 25.69 25.57 26.21 –0.85 –1.02 –0.9 –3.5 –0.4 LN

02 25.85 25.92 26.20 –0.87 –0.86 –0.8 6.7 2.0 LN

03 26.30 26.31 26.19 –0.83 –0.85 –0.7 –2.0 4.3 LN

04 26.79 26.71 26.19 –0.85 –0.81 –0.7 14.4 7.4 LN

05 26.97 26.92 26.23 –0.72 –0.73 –0.7 2.8 2.6 LN

06 26.93 26.86 26.30 –0.63 –0.61 –0.6 –9.6 –4.7 LN end

07 26.62 26.64 26.36 –0.45 –0.48 –0.5 –2.3 –1.4

08 26.38 26.39 26.37 –0.38 –0.41 –0.5 8.5 3.7

09 26.18 26.21 26.40 –0.44 –0.45 –0.5e 0.2 0.8

10 26.09 26.15 26.44 –0.54 –0.46 –0.4 –5.6 –3.1

11 26.22 26.18 26.48 –0.31 –0.38 –0.3 –1.4 –1.6

12 26.19 26.10 26.53 –0.35 –0.44 –0.4 2.1 2.7

1986 01 25.79 25.97 26.59 –0.75 –0.61 –0.5 8.0 1.9

02 26.12 26.20 26.65 –0.60 –0.58 –0.4 –10.7 –3.2

03 26.75 26.75 26.73 –0.38 –0.41 –0.2 0.8 –2.0

04 27.36 27.22 26.84 –0.28 –0.31 –0.2 1.2 –0.9

05 27.39 27.44 26.97 –0.30 –0.21 –0.1 –6.6 –0.3

06 27.61 27.50 27.09 0.05 0.03 0.0 10.7 4.3

07 27.38 27.37 27.23 0.31 0.26 0.3 2.2 1.9

08 27.11 27.24 27.39 0.35 0.43 0.5s –7.6 –4.6

09 27.34 27.36 27.53 0.72 0.70 0.7 –5.2 –3.0 EN start

10 27.63 27.58 27.66 1.00 0.97 0.9 6.1 –1.7 EN

11 27.70 27.65 27.77 1.17 1.09 1.1 –13.9 –8.8 EN

12 27.56 27.65 27.89 1.02 1.11 1.2 –13.6 –11.9 EN
73

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1987 01 27.77 27.76 27.99 1.23 1.18 1.2 –6.3 –9.7 EN

02 27.94 28.04 28.09 1.22 1.26 1.3p1 –12.6 –12.0 EN peak 1 (M)

03 28.50 28.40 28.18 1.37 1.25 1.2 –16.6 –17.6 EN

04 28.66 28.65 28.24 1.02 1.12 1.1 –24.4 –21.8 EN

05 28.77 28.78 28.27 1.08 1.14 1.0 –21.6 –21.9 EN

06 28.92 28.79 28.28 1.36 1.32 1.2 –20.1 –20.1 EN

07 28.56 28.60 28.27 1.49 1.49 1.4 –18.6 –17.8 EN

08 28.36 28.39 28.21 1.60 1.59 1.6p2 –14.0 –14.5 EN

09 28.28 28.26 28.14 1.66 1.60 1.6p2 –11.2 –10.5 EN peak 2 (S)

10 28.10 28.11 28.04 1.47 1.50 1.5 –5.6 –6.0 EN

11 27.94 27.91 27.90 1.41 1.35 1.3 –1.4 –3.2 EN

12 27.64 27.62 27.71 1.10 1.09 1.1 –4.5 –2.9 EN

1988 01 27.27 27.32 27.47 0.73 0.74 0.7 –1.1 –2.9 EN end

02 27.11 27.26 27.23 0.39 0.48 0.5e –5.0 –2.2

03 27.54 27.37 26.99 0.41 0.21 0.1 2.4 –0.4

04 27.28 27.23 26.73 –0.36 –0.30 –0.2 –1.3 2.5

05 26.82 26.79 26.44 –0.87 –0.86 –0.7s 10.0 3.7 LN start

06 26.23 26.10 26.17 –1.33 –1.23 –1.2 –3.9 3.4 LN

07 25.69 25.76 25.93 –1.38 –1.36 –1.3p1 11.3 8.4 LN peak 1 (M)

08 25.43 25.39 25.75 –1.33 –1.31 –1.2 14.9 15.3 LN

09 25.42 25.23 25.61 –1.20 –1.43 –1.3 20.1 17.4 LN

10 24.65 24.80 25.52 –1.98 –1.80 –1.6 14.6 17.6 LN

11 24.48 24.55 25.50 –2.05 –2.01 –1.9p2 21.0 16.9 LN peak 2 (VS)

12 24.60 24.58 25.55 –1.94 –1.99 –1.9p2 10.8 14.0 LN

1989 01 24.63 24.81 25.63 –1.91 –1.77 –1.7 13.2 11.6 LN

02 25.39 25.34 25.71 –1.33 –1.44 –1.5 9.1 9.5 LN

03 25.93 25.98 25.78 –1.20 –1.18 –1.1 6.7 10.9 LN

04 26.66 26.58 25.89 –0.98 –0.95 –0.8 21.0 15.9 LN

05 27.06 26.96 26.04 –0.63 –0.69 –0.6e 14.7 14.5 LN

06 27.04 26.98 26.19 –0.52 –0.50 –0.4 7.4 9.7 LN end

07 26.76 26.71 26.36 –0.31 –0.40 –0.3 9.4 5.0

08 26.29 26.43 26.51 –0.47 –0.38 –0.3 –6.3 0.6

09 26.37 26.34 26.65 –0.25 –0.32 –0.3 5.7 3.1

10 26.33 26.35 26.77 –0.30 –0.26 –0.3 7.3 4.6

11 26.36 26.38 26.87 –0.17 –0.17 –0.2 –2.0 –0.4

12 26.46 26.47 26.94 –0.02 –0.04 –0.1 –5.0 –3.3

1990 01 26.60 26.70 27.00 0.06 0.13 0.1 –1.1 –6.1

02 27.12 27.08 27.05 0.40 0.30 0.2 –17.3 –11.1

03 27.46 27.52 27.11 0.33 0.36 0.2 –8.5 –8.7

04 28.03 27.93 27.15 0.39 0.40 0.2 –0.5 0.9

05 28.19 28.03 27.19 0.50 0.38 0.2 13.1 6.7

06 27.69 27.74 27.22 0.13 0.27 0.2 1.0 5.2

07 27.37 27.37 27.26 0.30 0.26 0.3 5.5 1.8

08 27.05 27.09 27.28 0.29 0.28 0.3 –5.0 –3.0

09 26.87 26.91 27.27 0.25 0.26 0.3 –7.6 –4.6

10 26.86 26.83 27.27 0.23 0.23 0.3 1.8 –2.3

11 26.73 26.81 27.27 0.20 0.25 0.3 –5.3 –2.8

12 26.90 26.91 27.30 0.36 0.37 0.4 –2.4 –1.3
74

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1991 01 27.09 27.04 27.35 0.55 0.46 0.4 5.1 2.1

02 27.08 27.15 27.38 0.36 0.38 0.3 0.6 –1.1

03 27.36 27.45 27.39 0.23 0.29 0.3 –10.6 –8.4

04 27.98 27.91 27.43 0.34 0.38 0.4 –12.9 –13.9

05 28.30 28.23 27.51 0.61 0.59 0.6s –19.3 –14.3 EN start

06 28.34 28.20 27.60 0.78 0.79 0.8 –5.5 –8.0 EN peak 1 (W)

07 27.84 27.83 27.70 0.77 0.72 1.0p1 –1.7 –4.1 EN

08 27.30 27.36 27.80 0.54 0.55 0.9 –7.6 –8.4 EN

09 26.98 27.23 27.92 0.36 0.57 0.9 –16.6 –13.4 EN

10 27.64 27.51 28.03 1.01 0.91 1.0 –12.9 –12.4 EN

11 27.79 27.86 28.11 1.26 1.30 1.4 –7.3 –11.1 EN

12 28.20 28.10 28.14 1.66 1.56 1.6 –16.7 –16.5 EN

1992 01 28.19 28.24 28.12 1.65 1.66 1.8p2 –25.4 –19.2 EN peak 2 (S)

02 28.39 28.43 28.08 1.67 1.66 1.6 –9.3 –17.1 EN peak 2 (S)

03 28.76 28.77 28.04 1.63 1.62 1.5 –24.2 –19.1 EN

04 29.18 28.81 27.98 1.54 1.54 1.4 –18.7 –15.3 EN

05 29.13 28.92 27.87 1.44 1.27 1.2 0.5 –7.6 EN

06 28.22 28.27 27.75 0.66 0.80 0.8 –12.8 –8.0 EN end

07 27.50 27.49 27.63 0.43 0.37 0.5e –6.9 –6.3

08 26.73 26.89 27.53 –0.03 0.09 0.2 1.4 –0.8

09 26.61 26.59 27.43 –0.01 –0.07 0.0 0.8 –3.6

10 26.39 26.48 27.37 –0.24 –0.13 –0.1 –17.2 –10.2

11 26.51 26.51 27.33 –0.02 –0.05 0.0 –7.3 –9.3

12 26.63 26.66 27.32 0.09 0.12 0.2 –5.5 –6.6

1993 01 26.86 26.88 27.33 0.32 0.30 0.3 –8.2 –7.5

02 27.18 27.24 27.35 0.46 0.46 0.4 –7.9 –8.1

03 27.73 27.83 27.38 0.60 0.68 0.6 –8.5 –11.5 EN start

04 28.68 28.47 27.42 1.04 0.95 0.7 –21.1 –14.7 EN

05 28.79 28.65 27.47 1.10 1.00 0.8 –8.2 –13.4 EN peak (M)

06 28.33 28.25 27.49 0.77 0.78 0.7 –16.0 –12.8 EN

07 27.55 27.62 27.49 0.48 0.50 0.4 –10.8 –12.9 EN end

08 27.04 27.16 27.45 0.28 0.36 0.4 –14.0 –11.6

09 27.01 27.04 27.41 0.39 0.38 0.4 –7.6 –10.7

10 27.09 27.03 27.35 0.46 0.43 0.4 –13.5 –8.5

11 26.94 26.94 27.28 0.41 0.38 0.3 0.6 –2.7

12 26.77 26.77 27.23 0.23 0.24 0.2 1.6 0.6

1994 01 26.61 26.65 27.21 0.07 0.06 0.2 –1.6 –0.3

02 26.60 26.75 27.21 –0.12 –0.03 0.2 0.6 –2.8

03 27.19 27.20 27.24 0.06 0.04 0.3 –10.6 –10.9

04 27.80 27.70 27.26 0.16 0.17 0.4 –22.8 –17.3

05 28.00 27.94 27.32 0.31 0.30 0.5s –13.0 –14.8

06 27.96 27.83 27.40 0.40 0.36 0.5 –10.4 –13.0

07 27.38 27.53 27.49 0.31 0.42 0.6 –18.0 –15.9

08 27.40 27.33 27.58 0.64 0.53 0.6 –17.2 –17.4 EN start

09 27.15 27.33 27.64 0.53 0.68 0.7 –17.2 –16.4 EN

10 27.63 27.55 27.68 1.00 0.95 0.9 –14.1 –13.2 EN

11 27.79 27.75 27.68 1.26 1.20 1.2 –7.3 –10.1 EN

12 27.80 27.77 27.67 1.26 1.23 1.3p –11.6 –8.6 EN peak (M)
75

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1995 01 27.68 27.70 27.66 1.14 1.12 1.2 –4.0 –5.6 EN

02 27.64 27.68 27.61 0.92 0.90 0.9 –2.7 –1.5 EN

03 27.75 27.80 27.53 0.62 0.64 0.7e 3.5 –3.0 EN end

04 28.04 27.93 27.43 0.40 0.41 0.4 –16.2 –9.5

05 27.89 27.90 27.28 0.20 0.25 0.3 –9.0 –8.9

06 27.77 27.67 27.12 0.21 0.20 0.2 –1.5 –2.0

07 27.26 27.45 26.96 0.19 0.08 0.0 4.2 1.9

08 26.50 26.61 26.83 –0.26 –0.19 –0.2 0.8 2.3

09 26.18 26.22 26.72 –0.44 –0.44 –0.5s 3.2 1.5

10 26.01 26.02 26.66 –0.62 –0.59 –0.6 –1.3 0.5 LN start

11 25.87 25.90 26.61 –0.66 –0.66 –0.7p 1.3 –1.1 LN peak (W)

12 25.86 25.88 26.59 –0.68 –0.66 –0.7p –5.5 –0.3 LN peak (W)

1996 01 25.93 25.96 26.57 –0.61 –0.63 –0.7p 8.4 3.1 LN

02 26.10 26.23 26.57 –0.62 –0.55 –0.7p 1.1 4.2 LN end

03 26.78 26.77 26.58 –0.35 –0.38 –0.5e 6.2 5.3

04 27.43 27.28 26.61 –0.21 –0.25 –0.3 7.8 5.8

05 27.46 27.48 26.65 –0.23 –0.17 –0.1 1.3 6.1

06 27.57 27.42 26.68 0.01 –0.05 –0.1 13.9 9.0

07 27.08 27.08 26.70 0.01 –0.04 0.0 6.8 8.0

08 26.58 26.66 26.73 –0.18 –0.14 –0.1 4.6 5.7

09 26.41 26.47 26.76 –0.21 –0.19 –0.1 6.9 5.7

10 26.46 26.42 26.81 –0.17 –0.18 –0.2 4.2 3.8

11 26.35 26.33 26.89 –0.18 –0.20 –0.3 –0.1 2.8

12 26.16 26.21 27.00 –0.28 –0.28 –0.4 7.2 4.6

1997 01 26.15 26.25 27.12 –0.39 –0.31 –0.4 4.1 7.2

02 26.53 26.60 27.29 –0.19 –0.18 –0.3 13.3 5.6

03 27.19 27.26 27.48 0.06 0.10 0.0 –8.5 –5.0

04 28.11 28.04 27.69 0.47 0.51 0.4 –16.2 –15.8 EN start

05 28.74 28.61 27.91 1.05 0.96 0.8s –22.4 –21.3 EN

06 28.84 28.81 28.14 1.28 1.34 1.3 –24.1 –20.0 EN

07 28.83 28.83 28.37 1.76 1.71 1.7 –9.5 –15.7 EN

08 28.81 28.83 28.59 2.05 2.02 2.0 –19.8 –16.0 EN

09 28.85 28.88 28.75 2.23 2.23 2.2 –14.8 –16.8 EN

10 29.02 28.99 28.84 2.39 2.39 2.4 –17.8 –16.4 EN

11 29.08 29.02 28.85 2.55 2.46 2.5p –15.2 –14.3 EN peak (VS)

12 28.89 28.97 28.78 2.35 2.43 2.5p –9.1 –14.2 EN

1998 01 29.00 28.93 28.62 2.46 2.35 2.3 –23.5 –18.8 EN

02 28.84 28.86 28.41 2.12 2.07 1.9 –19.2 –22.6 EN

03 28.75 28.75 28.17 1.62 1.60 1.5 –28.5 –25.2 EN

04 28.67 28.66 27.90 1.03 1.14 1.0 –24.4 –19.2 EN

05 28.55 28.27 27.60 0.86 0.62 0.5e 0.5 –3.4 EN end

06 27.30 27.41 27.29 –0.26 –0.06 0.0 9.9 8.7

07 26.49 26.58 26.97 –0.58 –0.54 –0.5s 14.6 12.2 LN start

08 26.04 26.13 26.66 –0.72 –0.68 –0.8 9.8 11.3 LN

09 25.93 25.86 26.41 –0.69 –0.80 –1.0 11.1 10.7 LN

10 25.54 25.61 26.24 –1.09 –0.99 –1.1 10.9 11.4 LN

11 25.43 25.37 26.11 –1.10 –1.19 –1.3 12.5 12.3 LN

12 25.08 25.16 26.02 –1.46 –1.38 –1.4p1 13.3 13.7 LN
76

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

1999 01 25.05 25.13 25.99 –1.49 –1.45 –1.4p1 15.6 13.3 LN peak 1 (M)

02 25.35 25.52 25.98 –1.37 –1.26 –1.2 8.6 9.9 LN

03 26.34 26.25 25.97 –0.79 –0.91 –0.9 8.9 11.2 LN

04 26.96 26.81 25.98 –0.68 –0.71 –0.8 18.5 11.8 LN

05 26.99 26.92 25.98 –0.70 –0.73 –0.8 1.3 5.5 LN

06 26.74 26.72 25.97 –0.82 –0.76 –0.8 1.0 2.0 LN

07 26.39 26.35 25.96 –0.68 –0.76 –0.9 4.8 3.2 LN

08 25.89 26.02 25.94 –0.87 –0.78 –0.9 2.1 2.2 LN

09 25.91 25.85 25.92 –0.71 –0.81 –1.0 –0.4 2.6 LN

10 25.70 25.64 25.91 –0.93 –0.97 –1.1 9.1 7.7 LN

11 25.24 25.31 25.91 –1.29 –1.25 –1.3 13.1 12.0 LN

12 25.04 25.03 25.92 –1.50 –1.51 –1.6p2 12.8 11.0 LN

2000 01 24.79 24.96 25.94 –1.75 –1.62 –1.6p2 5.1 9.0 LN peak 2 (S)

02 25.23 25.31 25.98 –1.49 –1.47 –1.4 12.9 10.1 LN

03 26.00 26.05 26.02 –1.13 –1.11 –1.0 9.4 12.1 LN

04 26.97 26.75 26.06 –0.67 –0.77 –0.8 16.8 11.7 LN

05 27.07 27.01 26.11 –0.62 –0.64 –0.6 3.6 4.6 LN

06 26.93 26.90 26.16 –0.63 –0.58 –0.5e –5.5 –2.8 LN end

07 26.65 26.69 26.23 –0.42 –0.43 –0.4 –3.7 –1.9

08 26.52 26.51 26.30 –0.24 –0.29 –0.4 5.3 4.2

09 26.36 26.36 26.37 –0.26 –0.30 –0.4 9.9 8.7

10 26.18 26.16 26.43 –0.45 –0.45 –0.5s 9.7 12.9

11 25.91 25.92 26.47 –0.62 –0.64 –0.6 22.4 15.6

12 25.67 25.74 26.52 –0.87 –0.80 –0.7p 7.7 11.7

2001 01 25.70 25.80 26.57 –0.84 –0.79 –0.6 8.9 9.4

02 26.13 26.19 26.60 –0.59 –0.59 –0.5e 11.9 9.9

03 26.78 26.79 26.62 –0.35 –0.37 –0.4 6.7 6.4

04 27.47 27.32 26.64 –0.17 –0.20 –0.2 0.3 –0.4

05 27.57 27.55 26.67 –0.12 –0.10 –0.1 –9.0 –4.0

06 27.58 27.49 26.71 0.02 0.02 0.1 1.8 –2.1

07 27.24 27.22 26.76 0.17 0.10 0.2 –3.0 –3.3

08 26.80 26.83 26.81 0.04 0.03 0.2 –8.9 –4.9

09 26.47 26.55 26.86 –0.15 –0.11 0.1 1,4 –2.0

10 26.47 26.45 26.91 –0.16 –0.16 0.0 –1.9 1.2

11 26.37 26.34 26.95 –0.16 –0.22 –0.1 7.2 0.9

12 26.13 26.27 27.00 –0.41 –0.27 –0.1 –9.1 –2.1

2002 01 26.44 26.44 27.06 –0.10 –0.14 –0.1 2.7 1.0

02 26.76 26.83 27.11 0.04 0.05 0.1 7.7 3.2

03 27.36 27.35 27.19 0.23 0.19 0.2 –5.2 –1.6

04 27.91 27.81 27.29 0.27 0.29 0.4 –3.8 –6.8

05 28.07 28.11 27.42 0.38 0.46 0.7s –14.5 –9.8

06 28.37 28.15 27.57 0.81 0.68 0.8 –6.3 –8.7 EN start

07 27.80 27.89 27.70 0.73 0.77 0.9 –7.6 –9.0 EN

08 27.57 27.63 27.77 0.81 0.83 1.0 –14.6 –11.1 EN

09 27.57 27.65 27.81 0.95 0.99 1.1 –7.6 –9.3 EN

10 27.89 27.85 27.82 1.26 1.25 1.3 –7.4 –7.1 EN

11 28.06 28.00 27.78 1.53 1.45 1.5p –6.0 –7.5 EN peak (M)

12 28.00 27.91 27.72 1.46 1.34 1.4 –10.6 –7.3 EN
77

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

2003 01 27.56 27.63 27.66 1.02 1.05 1.2 –2.0 –5.5 EN

02 27.40 27.53 27.62 0.68 0.75 0.9 –7.4 –5.9 EN

03 27.74 27.66 27.56 0.61 0.50 0.5e –6.8 –6.6 EN end

04 27.74 27.64 27.51 0.10 0.12 0.1 –5.5 –6.3

05 27.34 27.48 27.43 –0.35 –0.17 –0.1 –7.4 –8.1

06 27.50 27.43 27.35 –0.06 –0.04 0.1 –12.0 –7.1

07 27.37 27.29 27.27 0.30 0.18 0.4 2.9 –2.0

08 26.92 27.03 27.22 0.16 0.23 0.5 –1.8 –0.7

09 26.90 26.98 27.18 0.28 0.32 0.6 –2.2 –2.0

10 27.19 27.08 27.16 0.56 0.48 0.5 –1.9 –2.4

11 27.05 27.05 27.19 0.52 0.49 0.6 –3.4 0.3

12 26.91 26.93 27.23 0.37 0.39 0.4 9.8 1.2

2004 01 26.84 26.88 27.25 0.30 0.30 0.4 –11.6 –1.2

02 26.93 26.97 27.29 0.21 0.19 0.3 8.6 1.5

03 27.16 27.27 27.34 0.03 0.12 0.2 0.2 –1.6

04 27.83 27.70 27.37 0.19 0.17 0.2 –15.4 –4.4

05 27.96 27.89 27.39 0.27 0.25 0.3 13.1 –0.9

06 27.82 27.81 27.41 0.26 0.34 0.5s –14.4 –5.7

07 27.64 27.66 27.44 0.57 0.55 0.7 –6.9 –9.0 EN start

08 27.54 27.54 27.46 0.78 0.53 0.8 –7.6 –6.2 EN

09 27.42 27.46 27.48 0.80 0.80 0.9p –2.8 –4.2 EN peak (W)

10 27.46 27.40 27.50 0.83 0.80 0.8 –3.7 –4.9 EN peak (W)

11 27.27 27.33 27.52 0.74 0.77 0.8 –9.3 –7.6 EN

12 27.30 27.25 27.53 0.76 0.72 0.8 –8.0 –5.9 EN

2005 01 27.14 27.15 27.52 0.60 0.57 0.7 1.8 –8.4 EN end

02 27.02 27.18 27.47 0.30 0.40 0.5e –29.1 –14.1

03 27.54 27.54 27.41 0.41 0.38 0.4 0.2 –10.0

04 28.05 27.95 27.34 0.41 0.43 0.4 –11.2 –9.2

05 28.16 28.07 27.26 0.47 0.43 0.4 –14.5 –9.4

06 27.91 27.80 27.16 0.35 0.33 0.4 2.6 –2.1

07 27.22 27.30 27.03 0.15 0.18 0.4 0.9 –0.6

08 26.83 26.89 26.93 0.07 0.09 0.3 –6.9 –2.3

09 26.67 26.69 26.85 0.05 0.03 0.2 3.9 3.0

10 26.59 26.52 26.78 –0.04 –0.09 –0.1 10.9 5.8

11 26.21 26.21 26.74 –0.32 –0.35 –0.4 –2.7 1.5

12 25.83 25.87 26.72 –0.71 –0.67 –0.7 0.6 2.8

2006 01 25.60 25.77 26.71 –0.94 –0.82 –0.7 12.7 6.5

02 26.05 26.06 26.73 –0.67 –0.72 –0.6 0.1 6.7

03 26.53 26.65 26.78 –0.60 –0.51 –0.4 13.8 10.7

04 27.47 27.31 26.85 –0.17 –0.22 –0.1 15.2 8.6

05 27.76 27.69 26.94 0.07 0.05 0.1 –9.8 –2.5

06 27.78 27.64 27.08 0.22 0.17 0.2 –5.5 –7.4

07 27.25 27.38 27.22 0.18 0.27 0.3 –8.9 –9.8

08 27.25 27.28 27.32 0.49 0.48 0.5s –15.9 –11.5

09 27.38 27.38 27.38 0.76 0.72 0.6 –5.1 –10.4 EN start

10 27.49 27.50 27.41 0.86 0.90 0.9 –15.3 –9.3 EN

11 27.64 27.62 27.41 1.11 1.06 1.1p –1.4 –5.3 EN peak (M)

12 27.69 27.55 27.38 1.15 1.01 1.1p –3.0 –3.7 EN
78

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued). 

Year Mon HadSST 2–mma 12–mma D(m) D(m2) ONI SOI* SOI(2) Comments**

2007 01 27.17 26.98 27.36 0.63 0.64 0.8e –7.3 –5.1 EN end

02 26.88 27.01 27.30 0.16 0.23 0.4 –2.7 –3.5

03 27.11 27.18 27.19 –0.02 0.02 0.1 –1.4 –2.1

04 27.61 27.45 27.03 –0.03 –0.08 –0.1 –3.0 –2.5

05 27.47 27.52 26.83 –0.22 –0.13 –0.1 –2.7 –0.9

06 27.52 27.34 26.61 –0.04 –0.13 –0.1 5.0 0.8

07 26.86 26.89 26.40 –0.21 –0.23 –0.1 –4.3 –0.2

08 26.31 26.30 26.23 –0.45 –0.51 –0.4 2.7 0.7 LN start

09 25.71 25.77 26.11 –0.91 –0.89 –0.7s 1.5 2.8 LN

10 25.33 25.36 26.04 –1.30 –1.24 –1.0 5.4 5.5 LN

11 25.07 25.11 26.00 –1.46 –1.45 –1.1 9.8 9.9 LN

12 24.98 24.96 25.97 –1.56 –1.58 –1.3 14.4 13.2 LN

2008 01 24.79 24.91 25.98 –1.75 –1.68 –1.4p 14.1 16.0 LN peak (S)

02 25.07 25.26 26.01 –1.65 –1.52 –1.4p 21.3 17.2 LN

03 26.09 26.03 26.07 –1.04 –1.12 –1.1 12.2 12.6 LN

04 26.88 26.77 26.14 –0.76 –0.76 –0.8 4.5 4.2 LN

05 27.22 27.14 26.24 –0.47 –0.51 –0.6e –4.3 0.2 LN end

06 27.24 27.22 26.32 –0.32 –0.25 –0.4 5.0 2.0

07 27.19 27.11 26.38 0.12 0.00 –0.1 2.2 4.6

08 26.83 26.83 26.46 0.07 0.03 0.0 9.1 8.6

09 26.47 26.55 26.52 –0.15 –0.11 0.0 14.1 12.7

10 26.43 26.41 26.56 –0.20 –0.20 0.0 13.4 14.5

11 26.29 26.18 – –0.24 –0.38 –0.3 17.1 15.2

12 25.69 25.81 – –0.85 –0.73 –0.6 13.3 13.3

2009 01 25.58 25.73 – –0.96 –0.86 –0.8 9.4 11.7

02 26.05 26.06 – –0.67 –0.72 –0.7 14.8 9.8

03 26.54 26.66 – –0.59 –0.49 –0.5 0.2 6.0

04 27.52 – – –0.12 – –0.1 8.6 3.1

05 – – – – – 0.2 –5.1 –1.0

06 – – – – – 0.6s –2.3 –2.0

07 – – – – – 0.7 1.6 –1.0

08 – – – – – 0.8 –5.0 –1.1

09 – – – – – 0.9 3.9 –3.0

10 – – – – – 1.2 –14.7 –8.1

11 – – – – – 1.5 –6.7 –8.8

12 – – – – – 1.8p –7.0 –7.7

2010 01 – – – – – 1.7 –10.1 –10.4

02 – – – – – – –14.5 –

Notes: HadSST = monthly values of the average temperature of the Niño 3.4 region, available at <http://www.cdc.noaa.gov/gcos_wgsp/Timeseries/Data/nino34.

 long.data>.

M = mean (1871–2008), M = 26.95.

sd = standard deviation (1871–2008), sd = 0.87.

CV = coefficient of variation (1871–2008), CV = sd/M = 0.032.

m = median (1871–2008), m = 26.96.

PCS = Pearson Coefficient of Skewness (1871–2008), PCS = 3(M–m)/sd = –0.034.

na = number of monthly values above median (1871–2008), na = 828.

nb = number of monthly values below median (1871–2008), nb = 828.

nra = number of runs above median (1871–2008), nra = 120.

z = the normal deviate of the monthly values (1871–2008), z = –28.94, a value indicating that the distribution of HadSST is highly nonrandom.
79

Table 7. SST monthly values of the Niño 3.4 region in degrees Celsius based on HadSST

time series, ONI and SOI values, and the occurrences of EN (warm) 

and LN (cold) events from 1871 to the present (Continued).

2-mma = 2-month moving average.

12-mma = 12-month moving average.

D(m) = difference between HadSST and the monthly-adjusted average (1871–2008).

D(m2) = 2-mma of D(m).

ONI = Oceanic Niño Index based on ERSST.v3b, available at <http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/

 ensoyears.shtml>.

* means SOI monthly values for 1871–1875 were taken from <http://www.cdc.noaa.gov/gcos_wgsp/Timeseries/Data/soi.long.data> 

 and multiplied by 10; values from 1876–present were taken from <http://www.bom.gov.au/climate/current/soihtml.shtml>.

** means EN/LN determination based on D(m2).

EN means El Niño.

LN means La Niña.

M in comments column means moderate strength.

S means strong strength.

VS means very stong strength.

W means weak strength.

b means event start before, using ONI.

e means event end, using ONI.

p means event peak, using ONI.

s means event start, using ONI.

Monthly-adjusted averages of HadSST:

1871–2008

January 26.54

February 26.72

March 27.13

April 27.64

May 27.69

June 27.56

July 27.07

August 26.76

September 26.62

October 26.63

November 26.53

December 26.54
80
81

REFERENCES

 1. Rasmusson, E.; and Wallace, J.M.: “Meteorological Aspects of the El Niño/Southern 

Oscillation,” Science, Vol. 222, p. 1195, 1983.

 2. Wang, H.-J.; Zhang, R.-H.; Cole, J.; and Chavez, F.: “El Niño and the Related Phenomenon

Southern Oscillation (ENSO): The Largest Signal in Interannual Climate Variation,” PNAS, 

Vol. 96, p. 11,071, 1999.

 3. Trenberth, K.E.; and Stepaniak, D.P.: “Indices of El Niño Evolution,” J. Climate, Vol. 14, 

p. 1697, 2001.

 4. Ropelewski, C.F.; and Halpert, M.S.: “Global and Regional Scale Precipitation Patterns Associated With the El Niño/Southern Oscillation,” Mon. Wea. Rev., Vol. 115, p. 1606, 1987.

 5. Philander, S.G.: El Niño, La Niña and the Southern Oscillation, Academic Press, San Diego, CA, 

1990.

 6. Halpert, M.S.; and Ropelewski, C.F.: “Surface Temperature Patterns Associated With the 

Southern Oscillation,” J. Climate, Vol. 5, p. 577, 1992.

 7. Kane, R.P.: “Relationship of El Niño-Southern Oscillation and Pacific Sea Surface Temperature 

With Rainfall in Various Regions of the Globe,” Mon. Wea. Rev., Vol. 125, p. 1792, 1997.

 8. Fagan, B.M.: Floods, Famines, and Emperors: El Niño and the Fate of Civilizations, Basic Books, 

New York, NY, 1999.

 9. Glantz, M.H.: Currents of Change: Impacts of El Niño and La Niña on Climate and Society, 

Cambridge University Press, New York, NY, 2001.

10. McPhadden, M.J.; Zebiak, S.E.; and Glantz, M.H.: “ENSO as an Integrating Concept in Earth

Science,” Science, Vol. 314, p. 1740, 2006.

11. Trenberth, K.E.: “The Definition of El Niño,” Bull. Am. Meteor. Soc., Vol. 78, p. 2771, 1997.

12. Hanley, D.E.; Bourassa, M.A.; O’Brien, J.O.; et al..: “A Quantitative Evaluation of ENSO 

Indices,” J. Climate, Vol. 16, p. 1249, 2003.

13. Bejerknes, J.: “Atmospheric Teleconnections From the Equatorial Pacific,” Mon. Wea. Rev., 

Vol. 97, p. 163, 1969.
82

14. Neelin, J.D.; Battisti, D.S.; Hirst, A.C.; et al.: “ENSO Theory,” J. Geophys. Res., Vol. 103, 

p. 14,261, 1998.

15. Cane, M.A.: “The Evolution of El Niño, Past and Future,” Earth Planet. Sci. Lett., Vol. 230, 

p. 227, 2005.

16. Quinn, W.H.; Neal, V.T.; and Antúnez de Mayolo, S.: “El Niño Occurrences Over the Past Four

and a Half Centuries,” J. Geophys. Res., Vol. 92, p. 14,449, 1987.

17. Ortlieb, L.; and Macharé, J.: “Former El Niño Events: Records From Western South America,”

Global Planet. Change, Vol. 7, p. 181, 1993.

18. Ortlieb, L.: “The Documentary Historical Record of El Niño Events in Peru: An Update of the 

Quinn Record (Sixteenth Through Nineteenth Centuries),” in El Niño and the Southern Oscillation: Variability, Global and Regional Impacts, H. Diaz and V. Markgraf (eds.), Cambridge 

University Press,New York, NY, p. 207, 2000.

19. Smith, T.M.; Reynolds, R.W.; Peterson, T.C.; and Lawrimore, J.: “Improvements to NOAA’s 

Historical Merged Land-Ocean Surface Temperature Analysis (1880–2006),” J. Climate, Vol. 21, 

p. 2283, 2008.

20. National Oceanic and Atmospheric Administration, <http://www.cpc.noaa.gov/products/

analysis-monitoring/ensostuff/ensoyears.shtml>, Accessed 2009.

21. Wilson, R.M.: “Decadal Variation of the Number of El Niño Onsets and El Niño-Related 

Months and Estimating the Likelihood of El Niño Onset in a Warming World,” NASA/

TP—2009–215899, Marshall Space Flight Center, AL, June 2009.

22. Herbert, J.; and Dixon, R.W.: “Is the ENSO Phenomenon Changing as a Result of Global 

Warming?,” Phys. Geography, Vol. 23, p. 196, 2002.

23. Klotzbach, P.J.; and Gray, W.M.: “Extended Range Forecast of Atlantic Seasonal Hurricane 

Activity and U.S. Landfall Strike Probability for 2009,” Colorado State University, Ft. Collins, 

CO, December 10, 2008, <http://hurricane.atmos.colostate.edu/forecasts/>, Accessed 2009.

24. Saunders, M.; and Lea, A.: “Extended Range Forecast for Atlantic Hurricane 

Activity in 2009,” University College London, United Kingdom, December 5, 2008, 

<http://tropicalstormrisk.com/>, Accessed 2009.

25 Wilson, R.M.: “North Atlantic Basin Tropical Cyclone Activity in Relation to Temperature 

and Decadal-Length Oscillation Patterns,” NASA/TP—2009–215796, Marshall Space Flight 

Center, AL, June 2009.
83

26. Rayner, N.A.; Parker, D.E.; Horton, E.B.; et al.: “Global Analyses of Sea Surface Temperature, 

Sea Ice, and Night Marine Air Temperature Since the Late Nineteenth Century,” J. Geophys.

Res., Vol. 108, p. 4407, 2003.

27. National Oceanic and Atmospheric Administration, <http://esrl.noaa.gov/psd/gcos_wgsp/

Timeseries/Nino34/index.html>, Accessed 2009.

28. Bureau of Meteorology, <http://reg.bom.gov.au/climate/>, Accessed 2010.
84

REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining 

the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing 

this burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operation and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. 

Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid 

OMB control number.

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.

1. REPORT DATE (DD-MM-YYYY) 2. REPORT TYPE 3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S) 5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION

 REPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITOR’S ACRONYM(S)

11. SPONSORING/MONITORING REPORT NUMBER

12. DISTRIBUTION/AVAILABILITY STATEMENT

13. SUPPLEMENTARY NOTES

14. ABSTRACT

15. SUBJECT TERMS

16. SECURITY CLASSIFICATION OF:

a. REPORT b. ABSTRACT c. THIS PAGE

17. LIMITATION OF ABSTRACT 18. NUMBER OF

 PAGES

19a. NAME OF RESPONSIBLE PERSON

19b. TELEPHONE NUMBER (Include area code)

Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std. Z39-18

An Examination of the Hadley Sea-Surface Temperature Time 

Series for the Niño 3.4 Region

Robert M. Wilson

George C. Marshall Space Flight Center

Marshall Space Flight Center, AL 35812

National Aeronautics and Space Administration

Washington, DC 20546–0001

Unclassified-Unlimited

Subject Category 47

Availability: NASA CASI (443–757–5802)

Prepared by the Science and Exploration Vehicle Office, Science and Mission Systems Office

M–1281

Technical Publication

NASA/TP—2010–216432

Hadley sea-surface temperature, El Niño, La Niña, ENSO cycle, recurrence rates, ONI, SOI

01-05-2010

UU 94

VP62

U U U

The Hadley sea-surface temperature (HadSST) dataset is investigated for the interval 1871–2008. The purpose of this investigation is to 

determine the degree of success in identifying and characterizing El Niño (EN) southern (ENSO) extreme events, both EN and La Niña 

(LN) events. Comparisons are made against both the Southern Oscillation Index for the same time interval and with published values of 

the Oceanic Niño Index for the interval since 1950. Some 60 ENSO extreme events are identified in the HadSST dataset, consisting of 

33 EN and 27 LN events. Also, preferential associations are found to exist between the duration of ENSO extreme events and their maximum anomalous excursion temperatures and between the recurrence rate for an EN event and the duration of the last known EN event. 

Because the present ongoing EN is a strong event, it should persist 11 months or longer, inferring that the next EN event should not be 

expected until June 2012 or later. Furthermore, the decadal sum of EN-related months is found to have increased somewhat steadily 

since the decade of 1920–1929, suggesting that the present decade (2010–2019) possibly will see about 3–4 EN events, totaling about 

37 ± 3 EN-related months (i.e., months that meet the definition for the occurrence of an EN event).

STI Help Desk at email: help@sti.nasa.gov

STI Help Desk at: 443-757-5802
The NASA STI Program...in Profile

Since its founding, NASA has been dedicated to the 

advancement of aeronautics and space science. The 

NASA Scientific and Technical Information (STI) 

Program Office plays a key part in helping NASA 

maintain this important role.

The NASA STI Program Office is operated by 

Langley Research Center, the lead center for 

NASA’s scientific and technical information. The 

NASA STI Program Office provides access to 

the NASA STI Database, the largest collection of 

aeronautical and space science STI in the world. 

The Program Office is also NASA’s institutional 

mechanism for disseminating the results of its 

research and development activities. These results 

are published by NASA in the NASA STI Report 

Series, which includes the following report types:

• TECHNICAL PUBLICATION. Reports of 

completed research or a major significant 

phase of research that present the results of 

NASA programs and include extensive data 

or theoretical analysis. Includes compilations 

of significant scientific and technical data 

and information deemed to be of continuing 

reference value. NASA’s counterpart of peerreviewed formal professional papers but has less 

stringent limitations on manuscript length and 

extent of graphic presentations.

• TECHNICAL MEMORANDUM. Scientific 

and technical findings that are preliminary or of 

specialized interest, e.g., quick release reports, 

working papers, and bibliographies that contain 

minimal annotation. Does not contain extensive 

analysis.

• CONTRACTOR REPORT. Scientific and 

technical findings by NASA-sponsored 

contractors and grantees.

• CONFERENCE PUBLICATION. Collected 

papers from scientific and technical conferences, 

symposia, seminars, or other meetings sponsored 

or cosponsored by NASA.

• SPECIAL PUBLICATION. Scientific, technical, 

or historical information from NASA programs, 

projects, and mission, often concerned with 

subjects having substantial public interest.

• TECHNICAL TRANSLATION. 

English-language translations of foreign 

scientific and technical material pertinent to 

NASA’s mission.

Specialized services that complement the STI 

Program Office’s diverse offerings include creating 

custom thesauri, building customized databases, 

organizing and publishing research results...even 

providing videos.

For more information about the NASA STI Program 

Office, see the following:

• Access the NASA STI program home page at 

<http://www.sti.nasa.gov>

• E-mail your question via the Internet to 

<help@sti.nasa.gov>

• Fax your question to the NASA STI Help Desk 

at 443 –757–5803

• Phone the NASA STI Help Desk at 

443 –757–5802

• Write to:

NASA STI Help Desk

NASA Center for AeroSpace Information

7115 Standard Drive

Hanover, MD 21076–1320
National Aeronautics and

Space Administration

IS20

George C. Marshall Space Flight Center

Marshall Space Flight Center, Alabama

35812