Spring 2010

No. 20Contents
El Niño Outlook (April – October 2010)

1

JMA’s Seasonal Numerical Ensemble Prediction for Summer 2010

2

Warm Season Outlook for Summer 2010 in Japan

4

Summary of Asian Winter Monsoon 2009/2010 - Extremely low temperatures in northern
Asia and extremely high temperatures in southern Asia

5

Stratospheric sudden warming events in winter 2009/2010

7

Global Temperature in 20097

Extremely Negative Arctic Oscillation in winter 2009/2010

8

El Niño Outlook (April – October 2010)
The current El Niño conditions are likely to come to an
end in boreal spring. It is likely that the SST in the IOBW region will continue to be above normal into boreal summer.
Pacific Ocean
In March 2010, the SST deviation from a sliding 30year mean SST averaged over the NINO.3 region was +0.7°
C. The five-month running-mean value of NINO.3 SST
deviations was +1.1°C for January, and the Southern Oscillation Index for March was -0.7. In March, positive SST
anomalies were remarkable in the central equatorial Pacific(Figs. 1 and 3 a), while subsurface temperature anomalies
were remarkably positive in the eastern equatorial Pacificand negative near the date line (Figs. 2 and 3 b). In theequatorial Pacific, convective activities were above normal
near the date line in March, and westerly wind anomalies in
the lower troposphere were found across the equatorial Pacific during early March. On the other hand, easterly wind
anomalies were seen in the western part in late March.
Subsurface warm waters in the equatorial Pacific thatwill migrate eastward are likely to keep SST anomalies
positive over the central and eastern Pacific for one or twomonths ahead, and subsurface cool waters west of the warm
waters are expected to migrate eastward and help to cancelout the positive SST anomalies in the equatorial Pacific in
the months ahead.
JMA's El Niño prediction model predicts that NINO.3
SST deviations will become closer to normal in the months

(a)

(a)

(b)

(b)

Figure 1 Monthly mean (a) sea surface temperatures (SSTs)and (b) SST anomalies in the Pacific and Indian Ocean sectors in March 2010
The contour intervals are 1˚C in (a) and 0.5˚C in (b). The baseperiod for the normal is 1971 – 2000.

Tokyo Climate Center

Figure 2 Monthly mean depth-longitude cross sections of(a) temperatures and (b) temperature anomalies in theequatorial Pacific for March 2010
The contour intervals are 1˚C in (a) and 0.5˚C in (b). The baseperiod for the normal is 1979 – 2004.

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No. 20 | Spring 2010

(a)

(b)

Figure 3 Time-longitude cross section of (a) SST and (b) ocean heat content (OHC) anomalies along the equator in
the Pacific Ocean
OHC is defined here as the vertical average temperature to a depth of 300 m. The base periods for the normal are 1971 –2000 for (a) and 1979 – 2004 for (b).

ahead, and that they will be near normal in boreal summer(Fig. 4).
Considering all the above factors, the current El Niño
conditions are likely to come to an end in boreal spring.
It is likely that the SST in the NINO.WEST region willcontinue to be near normal* into boreal summer.
Indian Ocean
The SST averaged over the tropical Indian Ocean(IOBW) region has been mostly above normal* since boreal
autumn of last year. It is likely that the SST in the IOBW
region will continue to be above normal* into boreal summer.
Impacts on the global climate
In March, warmer-than-normal conditions over the regions from South Africa to Madagascar and the northern partof South America were consistent with common patterns
seen in past El Niño events.
*The normals for NINO.WEST (Eq. – 15°N, 130°E – 150°E)
and IOBW (20°S – 20°N, 40°E – 100°E) are defined as linear extrapolations with respect to a sliding 30-year period in order to remove the effects of long-term trends(Ichiro Ishikawa, Climate Prediction Division)

Figure 4 SST deviation outlook for NINO.3 as predicted by the El Niño prediction modelThis figure shows a time series of monthly SST deviations
for NINO.3 (5˚N – 5˚S, 150˚W – 90˚W). The thick linewith closed circles shows the observed SST deviation values, and the boxes show the values predicted for the next six
months by the El Niño prediction model. Each box denotes
the range into which SST deviation is expected to fall with aprobability of 70%.

JMA’s Seasonal Numerical Ensemble Prediction for Summer 2010
The JMA seasonal ensemble prediction for summer 2010
indicates that convections will be active in the Indian Ocean
and the Atlantic but inactive in the central and eastern part of
the tropical Pacific. As for the Asian monsoon region, inactive convections are predicted east of the Philippines, andare expected to induce westward extension of the North Pacific High. In the upper troposphere, cyclonic circulation
anomalies are predicted over the Eurasian continent, implying a weak Tibetan High and a southward shift of the subtropical jet over the Eurasian continent.

JMA operates the Coupled Ocean-atmosphere General
Circulation Model (CGCM) as a seasonal prediction tool.
The Ensemble Prediction System (EPS) used with the
CGCM for seasonal prediction adopts a combination of theinitial perturbation method and the lagged average forecasting (LAF) method. The prediction consists of fifty-one
members from six different initial dates (nine members are
run every five days from 17 March to 11 April). Details of
the prediction system and verification maps based on 30year hindcast experiments (1979 – 2008) are available at
http://ds.data.jma.go.jp/tcc/tcc/products/model/index.html.
Section 2 presents predicted global SST anomalies, andSection 3 describes predicted circulation fields in the tropics and sub-tropics associated with these anomalies. Finally,
the predicted circulation fields in the middle and high latitudes of the Northern Hemisphere are explained in Section
4.

1. Introduction
This report outlines JMA’s summer 2010 (June – August, JJA) dynamical seasonal ensemble prediction, which
was used as a basis for the Agency’s operational warmseason outlook issued on 22 April 2010.

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2. SST anomalies (Figure 5)
In March 2010, remarkable positive SST anomalies
were seen in the central equatorial Pacific, and SSTs in thetropical Indian Ocean were mostly above normal. The
NINO.3 region’s El Niño monitoring index value, whichshows the deviation from a sliding 30-year mean SST averaged over the NINO.3 region, was +0.7°C. This indicatesthat El Niño conditions continued after summer 2009. According to JMA’s El Niño outlook, it is likely that the current El Niño conditions will come to an end this spring.
The SST anomalies forecast by JMA’s seasonal numerical ensemble prediction system are shown in Figure 5.
Above-normal SSTs are predicted in the tropical Indian
Ocean and the tropical Atlantic, while below-normal values
are expected from the central to the eastern part of the equatorial Pacific.

Figure 5 Predicted SST anomalies for June – August 2010
(ensemble mean of 51 members)

dicted in the northwestern part of the tropical Pacific, while
cyclonic anomalies are expected around the Caribbean Sea.
Anomaly patterns of atmospheric circulation in the northwestern part of the tropical Pacific and the Caribbean Sea
reflect those of tropical convection activities. These features
imply that the Tibetan High seen in the upper troposphere is
weaker than normal, especially in northern and eastern parts,and that the subtropical jet over the Eurasian continentshows a southward shift. They also imply that the westward
extension of the North Pacific High is stronger than normal.

3. Circulation fields in the tropics and sub-tropics(Figure 6)
Above-normal precipitation is predicted over most of
the Indian Ocean and the equatorial Atlantic. In the Asianmonsoon region, above-normal precipitation is predictedfrom the equatorial Indian Ocean to the Maritime Continent, while below-normal amounts are expected east of thePhilippines.
Upper tropospheric velocity potential anomalies in thetropics are expected to be negative (i.e., more divergent)over the Indian Ocean and the Atlantic, reflecting active
precipitation patterns in the tropics, while positive (i.e.,
more convergent) anomalies are forecast from the central tothe eastern part of the Pacific. Positive velocity potential
anomalies east of the Philippines imply inactive convectionin the region.
In the upper troposphere, cyclonic circulation anomalies
are predicted in the northern part of the Eurasian continentand the northwestern part of the tropical Pacific, while anticyclonic anomalies are expected around the Caribbean Sea.
In the lower troposphere, anti-cyclonic anomalies are pre-4. Circulation fields in the middle and high latitudes of
the Northern Hemisphere (Figure 7)
Predicted 500-hPa height anomalies are expected to begenerally positive in the mid-latitudes and negative in partsof eastern Siberia and in the west of the United States.
Negative anomalies of sea level pressure are predictedaround the Sea of Okhotsk, implying that the northward
extension of the North Pacific High is possibly weaker thannormal.
(Takayuki Tokuhiro , Climate Prediction Division)

(a)

(ｃ)

(ｂ)

(ｄ)

Figure 6 Predicted atmospheric fields in the tropics and sub-tropics for June – August 2010 (ensemble mean of 51
members)(a) Velocity potential at 200 hPa (contours) and anomaly (shading). The contour interval is 2 x 106 m2/s.
(b) Precipitation (contours) and anomaly (shade). The contour interval is 2 mm/day.
(c) Stream function at 200 hPa (contours) and anomaly (shading). The contour interval is 16 x 106 m2/s.
(d) Stream function at 850 hPa (contours) and anomaly (shading). The contour interval is 5 x 106 m2/s.

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No. 20| Spring 2010

(a)

（ｂ)

Figure 7 Predicted atmospheric fields in the middle and high latitudes of the Northern Hemisphere forJune – August 2010 (ensemble mean of 51 members)(a) 500 hPa height (contours) and anomaly (shading). The contour interval is 60 m.
(b) Sea level pressure (contours) and anomaly (shading). The contour interval is 4 hPa.

Warm Season Outlook for Summer 2010 in JapanFor summer 2010, mean temperatures are likely to be
below or near normal in northern Japan, above or near normal in western Japan, and above normal in Okinawa/
Amami. Warm-season precipitation amounts are likely to be
above or near normal in northern and eastern Japan.

Since the predicted anomalous circulation pattern is
consistent with the results of statistical studies on the impacts of the above-normal IOBW SST after El Niño
events, and the 30-year hindcast calculated using the
JMA/MRI atmosphere-ocean coupled model shows a highlevel of skill in predicting this pattern, the outlook for thissummer is based mainly on the model’s results.

1. Outlook summary
JMA issued its outlook for the coming summer overJapan in February, and updated it in March and April. For
summer 2010, mean temperatures are likely to be below
or near normal in northern Japan with 40% probability forboth categories, above or near normal in western Japan
with 40% probability for both categories, and above normal with 60% probability in Okinawa/Amami. Warmseason precipitation amounts are likely to be above ornear normal in northern and eastern Japan with 40% probability for both categories (Figure 8) .

( Shuhei Maeda, Climate Prediction Division)

2. Outlook background
Simply put, the lingering impacts of the currently decaying El Niño on atmospheric circulation in East Asia
are the main influences behind the outlook.
According to the JMA/MRI atmosphere-ocean coupledmodel, the current El Niño conditions are likely to cometo an end this boreal spring, while the IOBW-region SST(see Article 1), whose variation is influenced by El Niño,
will remain above normal into boreal summer. In association with the above-normal SST in the IOBW region, acharacteristic atmospheric circulation anomaly pattern inthe tropics and the sub-tropics (consisting of lower threemonth precipitation anomalies around the Philippines andstronger westward extension of the North Pacific Highwith weaker northward extension around Japan) is predicted in the western Pacific.
The predicted anomalous circulation pattern suggeststhat the northern part of Japan may be influenced by
fronts and cold air from the north due to the weaker northward extension of the North Pacific high, while the southern part of the country is expected to be covered by the
westward-extended North Pacific high with above-normal
temperatures.

Tokyo Climate Center

Figure 8 Probabilistic forecasts of seasonal mean temperatures(upper) and precipitation amounts (lower) for June – August4

No. 20 | Spring 2010

Summary of Asian Winter Monsoon 2009/2010- Extremely low temperatures in northern Asia and extremely high temperatures in southern Asia
Surface climate conditions
In winter 2009/2010, northern Asian countries experienced lower than normal temperatures, and southern Asian
countries experienced higher than normal temperatures(Figure 9).
Figure 10 shows extreme climate events from December 2009 to February 2010. In December and February,
extremely low temperatures were observed from western
Siberia to Mongolia, and extremely high temperatures wereobserved from Indonesia to India. Furthermore, extremely
heavy precipitation (snow) amounts were observed fromeastern China to Central Asia. In January, extremely low
temperatures were observed in southwestern Siberia and innortheastern India, and extremely high temperatures wereobserved from central China to Indonesia and in western
India. Extremely heavy precipitation (snow) amounts werealso observed around northeastern China and around southern Central Asia.

(°C)
Figure 9
Seasonal temperature anomalies for winter(December – February) 2009/2010
Anomalies are deviations from the normal (i.e., the 1971 – 2000
average). The contour interval is 1°C.

(Takafumi Umeda, Climate Prediction Division)

DecemberJanuary

February

Figure 10 Extreme climate events from December 2009 to February 2010

parison with their normal forms, indicating a weaker-thannormal winter monsoon over these areas. In the tropics, an
El Niño event that started in summer 2009 continued into
boreal winter. In association with this, convective activities were weaker than normal in Indonesia and the western
Pacific, while they were stronger than normal in the central Pacific (Figure 14). In the lower troposphere, anticyclonic circulation was seen across Southeast Asia andsouth of Japan with its center in the Philippines. Abovenormal surface temperatures in Japan, the Philippines andMalaysia were consistent with the features of past El Niño
events (Figure 15).
(Shotaro Tanaka, Climate Prediction Division)

Conditions of convective activity and atmospheric circulation
During boreal winter 2009/2010 (December 2009 – February 2010), the negative phase of the Arctic Oscillation(AO) was significantly dominant (Figure 11). Associatedwith the AO pattern, below-normal anomalies in the 850hPa temperature field were observed from western Siberia
to Mongolia (Figure 12). The Siberian High was enhanced
in its northern part, and the Aleutian Low shifted eastward
from its normal position, which is usually around the dateline (Figure 13). In Japan and the southern part of China,
zonal gradients of sea level pressure were reduced in com-

Figure 11 Left panel: three-month averaged 500hPa height (contour) and anomaly (shading) for
December 2009 – February 2010;
right panel: regression map of the first leading
mode from empirical orthogonal function analysis of three-month averaged 500-hPa height (20 –90˚N) for December – February in the period
1979/1980 – 2004/2005
The base period for the normal is 1979 – 2004. JRA/JCDAS data were used in the analysis.

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Figure 12 Three-month averaged 850-hPa temperature(contours) and anomaly (shading) for December 2009 – February 2010
The contour interval is 4˚C, and the base period for the normal is1979 – 2004. Wavy hatch patterns indicate areas with altitudes
higher than 1,600 m. JRA/JCDAS data were used in the analysis.

Figure 13 Three-month averaged sea level pressure (contours)
and anomaly (shading) for December 2009 – February 2010
The contour interval is 4 hPa, and the base period for the normal is1979 – 2004. JRA/JCDAS data were used in the analysis.

Figure 14 Outgoing Longwave Radiation (OLR) anomaly (shading) and 850-hPa stream function anomaly(contours)
Warm/cold-color shading indicates weaker/stronger-thannormal convective activities. Original OLR data were provided by NOAA. The contour interval is 1 x 106 m2/s, andthe base period for the normal is 1979 – 2004. JRA/JCDAS
data were used in the stream function analysis.

Figure 15 Schematic map of typical temperatures and precipitation in El Niño eventsfor December – February
Shading indicates warm/cold and wet/dry areas at a 90% level of confidence, comparing El
Niño years with both non-El Niño and non-La Niña years for boreal winter (December –February) in the period 1979/1980 – 2008/2009.

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Stratospheric Sudden Warming Events in winter 2009/2010
In winter 2009/2010, stratospheric sudden warming (SSW)
events were observed in December 2009 and in February
2010, with the latter one being a major event.

In January 2010, the polar vortex moved southward until its center reached the vicinity of Lake Baikal, and a second SSW event occurred. It grew into a major occurrenceof SSW in early February 2010, and significantly abovenormal temperatures continued in the polar region throughout the month (Figure 16). During the period of the major
SSW event, the polar vortex maintained its split form, and areversion of zonal winds from westerlies to easterlies wasobserved in the region north of 60ºN (Figure 17).
In the troposphere, the negative phase of the Arctic Oscillation (AO) dominated throughout winter. It is conceivable that the stratospheric warm conditions seen in November 2009 contributed to the development of this negative
AO, and that the SSW events and negative AO influenced
each other during this winter period.

JMA’s Climate Prediction Division (CPD) routinely
monitors stratospheric circulation with a focus on detecting
SSW events and providing early notification of them. When
SSW occurs for the first time in a winter season, a
STRATALERT report is issued by JMA and disseminatedvia WMO’s Global Telecommunication System (GTS) on
that day and every day thereafter.
In November 2009, easterly wind anomalies in thezonal-mean wind field were observed over the polar region,and higher-than-normal temperatures were seen over Canada in the stratosphere. However, this event did not satisfy
the criteria to qualify as SSW.
From early to mid-December 2009, a minor SSW event
occurred and the polar vortex split into two in midDecember.

(Hiroshi Hasegawa and Nobuyuki Kayaba, Climate
Prediction Division)

Figure 16 Time series of temperatures at 30-hPa
level over the North Pole in winter 2009/2010
The black line shows temperatures for winter 2009/2010.
The gray line shows the climatological mean.

Figure 17 30-hPa geopotential height (contours) andanomalies (shading) during the major SSW event (9 –27 February 2010)
The contour interval is 120 m.

Global Temperature in 2009
The annual global average surface temperature anomaly
for 2009 was +0.31ºC – the third highest on record since 1891.

Table 1 Annual global mean temperature rankings

The annual global average surface temperature anomaly
for 2009 (i.e., the average of the near-surface air temperature over land and the sea surface temperature) was +0.31°
C ±0.13°C above normal (based on the 1971 – 2000 average), which tied with 2006, 2003 and 2002 as the third
highest on record since 1891 (Table 1, Figure 18).

Annual land surface temperatures were above normal in most parts of the world except for North America and central Siberia. Sea surface temperatures wereYear

Temperature
anomaly

1
2
3

1998
2005
2009
2006
2003
2002
2007
2004
2001
1997

+0.37
+0.32
+0.31
+0.31
+0.31
+0.31
+0.28
+0.27
+0.27
+0.24

7
8

high, especially in the tropical Pacific and the Indian Ocean(Figure 19).

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Rank

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No. 20 | Spring 2010

In particular, the high global temperature for 2009 canbe attributed to the El Niño phenomenon, which started todevelop in the summer of that year.
For more information, please refer to http://
ds.data.jma.go.jp/tcc/tcc/products/gwp/temp/ann_wld.html.

On a longer time scale, global average surface temperatures have been increasing at a rate of 0.68°C per century(Figure 18).The high temperatures seen in recent years havebeen influenced by fluctuations over different time scales
ranging from several years to several decades, as well as byglobal warming resulting from the increased presence ofgreenhouse gases such as CO2.

(Shoji Hirahara, Climate Prediction Division)

Figure 18 Annual anomalies in global
average surface temperature from 1891
to 2009
The bars indicate the annual anomaly of the
global average surface temperature and90% confidence intervals for each year.
The blue line indicates five-year runningmean, and the red line shows the long-term
linear trend.

Figure 19 Annual surface temperature
anomalies for 2009
The circles indicate temperature anomalies
from the climatological normal (i.e., the 1971
– 2000 average) averaged in individual 5° x
5° grid boxes.

Extremely Negative Arctic Oscillation in winter 2009/2010
temperatures were observed (Figure 20). The Japan Meteorological Agency (JMA) held a meeting of the Advisory
Panel on Extreme Climatic Events, which consists of 10
prominent experts from universities and research institutes,
to provide it with advice on the causes of these prevailingextreme cold waves. Based on the guidance of the Panel,
JMA issued a statement on the atmospheric circulation that
had led to the extreme climatic events. This article is basedon that statement.

Overview of the climate in winter 2009/2010
Many parts of the mid-latitudes in the Northern Hemisphere experienced severely cold days during the winter of
2009/2010. In particular, seasonal mean temperatures were
extremely low in Siberia, Mongolia, northern China, theUnited States of America and Europe (except for the Mediterranean region), and record-breaking heavy snowfall wasobserved in some of these regions. Meanwhile, from thenortheastern part of Canada to Greenland, extremely highFigure 20 Normalized three-month mean temperature anomaly for winter (Dec. – Feb.) 2009/2010

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Characteristics of the extremely negative Arctic Oscillation (AO) seen in winter 2009/2010
In the winter of 2009/2010, high-pressure systems developed over the Arctic, while low-pressure anomalies were
dominant in the surrounding mid-latitudes with the southward-shifted and enhanced Icelandic low and Aleutian low(Figure 21). The Arctic Oscillation (AO) is well known as
an annular mode representing the first dominant mode of
atmospheric circulation variation in boreal winter as obtained from EOF analysis. The anomaly distribution in the
sea-level pressure field during this winter reflected an extremely negative phase of the AO. The AO index, which
was developed based on EOF analysis of monthly mean sea
level pressure, showed its lowest value in the winter of
2009/2010 since 1979/1980 (Figure 22). It can be said thatthe dominance of the negative AO was an important featureof atmospheric circulation in the winter of 2009/2010. The
negativity developed in December 2009 before temporarily
weakening in mid-January 2010 and then developing again
in early February 2010. In association with this remarkablenegative AO, cold air masses frequently flowed to the Eurasian continent and North America. Nonetheless, temperatures were above normal over Japan because the Aleutian
low shifted eastward from its normal position and highpressure with warm air masses developed to the south ofJapan. These features of atmospheric circulation around
Japan are consistent with those commonly seen during El
Niño events.

Figure 21 Three-month mean sea level pressure for winter(Dec. – Feb.) 2009/2010

Development and maintenance of negative AO
In association with the negative phase of the AO, thesubtropical jet was relatively strong, while the polar front
jet was unclear (weaker-than-normal zonal winds between
50°N and 60°N) during winter 2009/2010 (Figure 23). Thisanomaly pattern of zonal winds seemed to be maintained
through positive feedback between the mean flow and eddies (e.g., Kimoto et al., 2001). A blocking high-pressure
system developed over Alaska through the propagation of
Rossby wave packets from active convection over the tropical western Pacific, thereby triggering a negative AO.
Stratospheric sudden warming events occurring in early
December may also have played an important role in thedevelopment and maintenance of this negative AO. It isnecessary to further investigate the effects of these eventson the features of this negative AO.

Figure 22 Time-series of the AO index for winter (Dec. –Feb.)
EOF analysis is applied to each monthly mean sea-level pressure (SLP) north of 20°N year-round, then the annular modes ofeach EOF are averaged to give an annual AO mode. Scores arecalculated by projecting historical SLP fields to the AO mode.

(Shingo Ushida, Climate Prediction Division)
Reference
Kimoto, M., F. Jin, M. Watanabe and N. Yasutomi (2001), Zonaleddy coupling and a neutral mode theory for the Arctic Oscillation, Geophys. Res. Lett., 28 (4), 737 – 740
Figure 23 Three-month mean zonal averaged zonal windspeed and anomaly in winter (Dec. – Feb.) 2009/2010

Any comments or inquiries on this newsletter and/or the Tokyo Climate Center (TCC), Climate Prediction Division, JMA
TCC website would be much appreciated. Please e-mail Address: 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan
to: tcc@climar.kishou.go.jp
TCC website: http://ds.data.jma.go.jp/tcc/tcc/index.html(Chief Editor: Kumi Hayashi)Tokyo Climate Center

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No. 20 | Spring 2010