Summer 2008

No. 13
Contents
Summary of the 2007/2008 La Niña Event1

Summary of Yellow Sand over Japan in 2008

4

Sea Ice in the Sea of Okhotsk for the 2007/2008 Winter Season

5

Atmospheric Circulation Anomalies behind US Midwest Flooding in June 2008

6

WMO Working Group on Climate-Related Matters for Regional Association II

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Hands-on Training for Climate Data Communication and Applications at TCC

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Summary of the 2007/2008 La Niña Event
A La Niña event occurred from spring 2007 to spring 2008
for the first time since the 2005/2006 occurrence. In this
2007/2008 event, the minimum value of five-month runningmean sea surface temperature (SST) deviations for the
NINO.3 region was –1.5˚C, which equaled the record lows of
the 1988/1989 and 1998–2000 La Niña events.
1.

Outline of the 2007/2008 La Niña event
The Japan Meteorological Agency (JMA) monitors the
SST of the NINO.3 region (5°S–5°N, 150°E–90°E), whereinter-annual variability is the largest in the equatorial Pacific, to identify El Niño/La Niña events (http://

ds.data.jma.go.jp/tcc/tcc/products/elnino/index.html). The
five-month running mean value of NINO.3 SST deviationfrom the latest 30-year sliding mean was equal to or below–0.5°C for 13 consecutive months from April 2007 to April
2008, as shown in Table 1. A La Niña event occurred fromspring 2007 to spring 2008, according to JMA’s definitionof a La Niña event (i.e., the five-month running mean SST
deviation for the NINO.3 region is –0.5°C or below for six
consecutive months or longer). This was the first La Niña
event since the 2005/2006 occurrence, and the 13th such
event since 1949 (Table 2).

Table 1 El Niño Monitoring Indices from January 2007 to June 2008
SST values consist of monthly mean sea surface temperatures averaged over the NINO.3 region (5˚S–5˚N, 150˚W–90˚W).
SST deviation for the NINO.3 region is defined as the difference between the monthly mean SST and the climatologicalmean for a sliding 30-year period. Five-month mean values in italics with blue shading indicate levels below –0.5˚C and thata La Niña event is ongoing. Numbers in red indicate SST minima during the 2007/2008 La Niña event.

Table 2 List of historical La Niña events since 1949 based on JMA’s definition along with duration seasons/months
and minimum values of five-month/monthly mean NINO.3 SST
Numbers in red indicate record lengths in terms of duration and minimum records in terms of NINO.3 SST.

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The 2007/2008 La Niña event was a typical one thatdeveloped from spring, continued for about a year and decayed in the spring of the following year. In this event, theminimum value of the five-month running mean NINO.3
SST deviation was –1.5˚C, which equaled the record lowsof the 1988/1989 and 1998–2000 La Niña events. The
minimum value of monthly mean NINO.3 SST deviation
was –1.7˚C, which is the joint third largest along with the
1954–1956 occurrence, after the –1.8˚C value of the
1988/1989 and 1998–2000 La Niña events.
2. Progress of the 2007/2008 La Niña event
Figure 1 shows a time-longitude cross section of fiveday averaged SST anomalies along the equator in the Pacific Ocean. In January 2007, positive SST anomalies were
widely found in the equatorial Pacific. In March 2007, remarkably negative SST anomalies appeared east of 150˚W
in the NINO.3 region. An SST anomaly pattern typical of
those seen during La Niña events (i.e., negative in the eastern equatorial Pacific and positive in the western part) remained until August 2007. In September 2007, remarkably
negative SST anomalies expanded to the west of the dateline, widely covering the area from the central equatorial
Pacific to its eastern part. Thereafter, remarkably negative
SST anomalies gradually extended westward, and both
NINO.3 and NINO.4 SSTs became remarkably below normal in October 2007. In February 2008, the minimum values of negative SST anomalies in this event were widely
found from the date line to 120˚W. On the other hand, afterJanuary 2008, positive SST anomalies expanded graduallyfrom the coast of South America to the eastern equatorial
Pacific. In March 2008, remarkably positive SST anomalies were found east of 110˚W in the equatorial Pacific.
The negative SST anomalies from the central to the easternequatorial Pacific gradually shrank, and negative anomaliesof less than –0.5˚C were found only around the date line in

Figure 1 Time-longitude cross section of SST anomalies
along the equator in the Pacific Ocean
The base period for the normal is 1971–2000.

June 2008.
The processes of La Niña events are classified into theonset phase, the peak phase, the mature phase and the following phase, after Rasmusson and Carpenter (1982)(Figure 2).
During the onset phase from October to December(OND) 2006, positive anomalies were remarkable from thecentral to the eastern equatorial Pacific (Figure 2a). In thedepth-longitude cross section of three-month averaged
temperatures and anomalies (Figure 2e), positive anomalies in the eastern equatorial Pacific and negative anomalies in the western part were remarkable, indicating temporal El Niño-like features.
During the peak phase from April to June (AMJ) 2007,
when the La Niña event began to develop, negative SST
anomalies expanded over the eastern equatorial Pacific,
and monthly mean NINO.3 SST deviation wasfrom –0.5˚C to –0.7˚C (Table 1). Meanwhile,during the same period, positive SST anomalies
were found from the western to the central
equatorial Pacific (Figure 2b). In upper-ocean
temperatures along the equatorial Pacific, colder
waters that were found in the western part during the onset phase migrated to the eastern part,
resulting in remarkably negative temperature
anomalies in the eastern part and near-normal
ones in the western part (Figure 2f).
Duringthe mature phase from October to December
2007, negative SST anomalies expanded to thecentral and western equatorial Pacific, covering
most of the equatorial Pacific except for the
Figure 2 Three-month mean sea surface temperatures (SSTs) and anomalies in the Pacific andIndian Oceans (left) and depth-longitude crosssections of three-month mean temperatures andanomalies upper 300 m along the equatorial Pacific (right)
White contours indicate SSTs/temperatures at intervals of 5˚C. The top panels (a and e) show the onset
phase during OND 2006, the second ones down (band f) show the peak phase during AMJ 2007, thethird panels (c and g) show the mature phase during
OND 2007, and the bottom ones (d and h) show thefollowing phase during AMJ 2008 of La Niña
events. These phase names are those used by Rasmusson and Carpenter (1982).

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westernmost part (Figure 2c). During this period, the eastwest contrast of upper-ocean temperature anomalies (i.e.,
negative in the eastern part and positive in western part)was remarkable in the equatorial Pacific.
During the following phase from April to June 2008,
positive SST anomalies appeared in the eastern equatorial
Pacific, and negative SST anomalies were found only in thecentral part (Figure 2d). In the depth-longitude cross section along the equatorial Pacific, positive temperature
anomalies became remarkable in the western and easternparts, and positive anomalies along the thermocline depth
indicated deepening (Figure 2h). During this phase, negative SST anomalies in the central equatorial Pacific shrank
and weakened, resulting in the termination of the
2007/2008 La Niña event in spring 2008.
3.

Comparison with other historical events
We compared the progress of the 2007/2008 La Niña
event with other historical occurrences of the phenomenon.
Figure 3 shows time series composites of three-month running mean SST deviations averaged over the NINO.3 and
NINO.4 regions for historical La Niña events since 1949.
In the developing process (i.e., the starting year) of the
2007/2008 La Niña event, SST deviation in the NINO.3
region rapidly decreased from winter to early spring, and aslowdown of the decrease was found from spring to sum-mer. On the other hand, in 1970 and 1988, NINO.3 SST
deviations constantly fell and reach their minima during
summer. In 2007, NINO.3 SST deviation rapidly fell again
from summer, and reached its minimum from autumn towinter (Figure 3a). In the NINO.4 region for the 2007/2008
event, the reduction of SST deviation during spring andsummer was slower than that in NINO.3, and SST was nearnormal in July. SST deviation in NINO.4 decreased rapidly
in autumn, and reached its minimum in late winter. The
minimum in NINO.4 was found three months later than thatin NINO.3. The SST deviation in NINO.4 for 2007 reached
its minimum later than those for 1988 and 1998, but theminimum for 2007 had almost the same magnitude as thosefor 1988 and 1998 (Figure 3b).
In the decaying process (i.e., the finishing year) of the
2007/2008 La Niña events, the SST deviation in NINO.3
rose rapidly after its minimum from late autumn to early
winter, and returned to normal with almost the same timing
as in spring 1989 and 2000 (Figure 3c). On the other hand,
the minimum SST deviation of NINO.4 in the 2007/2008
event was found later than that of the 1988/1989 event.
The SST deviation of NINO.4 began to rise from the springof 2008. Due to the larger magnitude and later timing of
the minimum of NINO.4 deviation in the 2007/2008 event,the NINO.4 SST was still below normal in June 2008
(Figure 3d).

Figure 3 Time series composites of three-month running mean sea surface temperature (SST) deviations averaged
over the NINO.3 and NINO.4 regions for historical La Niña events
The upper panels (a and b) show composites for event-starting years, and the lower ones (c and d) show those for eventfinishing years. The panels on the left (a and c) show SST composites for the NINO.3 region, and those on the right (b and d)show composites for the NINO.4 region. Normal values are taken as the latest 30-year sliding mean SSTs to remove longterm trends. Year 0 in the upper panels represents the year that the La Niña event began and Year+1 means the following
year. The La Niña years are 1949, 1954, 1964, 1967, 1970, 1973, 1975, 1984, 1988, 1995, 1998, 2005 and 2007. Meanwhile
Year 0 in the lower panels represents the year that the La Niña event ended and Year-1 means the previous year.

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4. Impact on climate in Japan and around the world
During the 2007/2008 La Niña event, several significant
climate anomalies were observed around the world.
In South America, temperatures were lower than normal
in southern parts from May to August 2007 and along the
Pacific coast from September 2007 to February 2008. Drierconditions were found in northern parts. In North America,
warmer and drier conditions appeared in the eastern USA
during August 2007. Temperatures were warmer than normal in the southern USA and cooler than normal along the
Pacific coast during winter of 2007/2008. In Australia,
wetter conditions were found in northern parts from June toAugust, while drier conditions were found in eastern parts
from December 2007 to February 2008. Around the islandsof Indonesia, wetter conditions were found from August to

September. In Japan, warmer conditions were found from
August to September 2007.
Some of the above-mentioned climate anomalies are
consistent with those statistically seen during La Niña
events(http://ds.data.jma.go.jp/tcc/tcc/products/climate/
ENSO/shade/shadela.html).
Reference:
Rasmusson, E. M. and T. H. Carpenter 1982: Variations in
Tropical Sea Surface Temperature and Surface Wind Fields
Associated with the Southern Oscillation/El Niño. Mon.
Wea. Rev., 110, 354–384.
(Ikuo Yoshikawa, Climate Prediction Division)

Summary of Yellow Sand over Japan in 2008
The number of days when any meteorological station in
Japan observed yellow sand, or Aeolian dust, from January
to May 2008 was 10, which was the smallest since 1987.
Yellow sand was widely observed throughout the country
except northern Japan on 3 March, but was subsequently
observed only a few times, mainly in western Japan.
JMA carries out observation of the phenomenon at 85
meteorological stations. Yellow sand observed from 2 to
4 March originated from the Gobi Desert on 29 February
and spread over Japan along with a cyclone. This event
was also detected in MTSAT’s infrared differential imagery. In addition, JMA’s operational numerical dust
model (Model of Aerosol Species In the Global Atmosphere: MASINGAR) successfully forecasted the emission
and transportation of yellow sand as early as 28 February.
Since 27 February, a JMA web page providing Aeolian
dust information has provided current observation andprediction updates on yellow sand using different colors
to indicate its concentration (Figures 4 and 5).
(URL: http://www.jma.go.jp/en/kosa/index.html)
From 1 January to 31 May 2008, the number of days
when any meteorological station observed yellow sandwas 10, which was the smallest since 1987 (Figure 6).

Figure 4 Stations observing aeolian dust or local sand/dust
haze during the day
Colors indicate the lowest visibilities observed at these stations.

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Figure 5 Distribution of predicted concentrations of yellow
sand at a level of 0–1 km from the surface for 1.25 x 1.25
degree grid areas

Figure 6 Daily number of meteorological stations that observed yellow sand from 1 March to 31 May 2008 (total
number of meteorological stations: 85)
Yellow sand was not observed at any stations from January to
February.

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The total daily number of meteorological stations that observed the phenomenon in 2008 was 125, which was also
the smallest since 1997 (Figure 7). Of special interest isthat the total number of days when yellow sand was observed in April was only one, which was far below the normal value of 7.9.
Monthly CLIMAT data show heavy precipitation innortheastern parts of China in April and light precipitation
around the Gobi Desert from April to May. Moreover, theTaklimakan Desert experienced light precipitation fromMarch to May according to CLIMAT data averaged overthree months (Figure 8). According to SYNOP reports, thenumber of sandstorm and dust events around the Gobi Desert (95–115°E, 35–50°N) increased by about 25% compared to the previous year, suggesting a more frequent occurrence of yellow sand.
One possible cause of decreased observation of the phenomenon in Japan is that yellow sand rarely blew over thecountry, or did not reach ground level even if it was present.
Analysis of atmospheric circulation from March to May
indicates that the activity of cyclones was weaker than normal around Japan and prevailing westerlies in the middle
and upper troposphere did not meander. It is presumed
from this circulation pattern that the inflow of yellow sandalong with cyclones into Japan was reduced, and that thephenomenon moved zonally from the generation region to
the north of the country.

Figure 7 Annual total daily numbers of meteorological stations observing yellow sand from 1967 to 2008

Figure 8 Three-month mean precipitation ratio from March
to May 2008 according to CLIMAT data
The Gobi Desert and the Taklimakan Desert experienced light
precipitation.

(Atsuya Kinoshita, Atmospheric Environment Division)

Sea Ice in the Sea of Okhotsk for the 2007/2008 Winter Season
The sea ice extent in the Sea of Okhotsk was smaller
than normal for almost all the 2008 sea ice season (fromDecember 2007 to May 2008) (Figure 9). It reached its
seasonal maximum of 110.69 x 104 km2 on 10 February,
exceeding the highest value for the previous season(Figures 9 and 10). The accumulated sea ice extent was

smaller than the previous season (Figure 11), and its ratio tothe normal (the 1971–2000 average) was 80%.
Figure 11 shows overall trends for the period from 1971
to 2008. The maximum sea ice extent has fallen by about
15% of the area of the Sea of Okhotsk over approximately
the past 40 years. However, sea ice in the Sea of Okhotsk
is first-year ice (i.e., ice of not more than one winter’s
growth), and its interannual extent varies dramatically. As an example, the maximum sea ice
extent was 55% of thearea of the Sea of Okhotsk in 1984, while it
covered almost the entire
sea in 2001.
Smallchanges in meteorological and oceanographic
forcing could result insignificant changes in theextent and state of thesea ice cover.
(Keiji Hamada, Office ofMarine Prediction)

Figure 9 Variations in the five-day mean sea ice extent in
the Sea of Okhotsk from November 2007 to July 2008

Figure 10 Sea ice conditions for 10 February 2008
The white area shows the observed sea ice extent, and the redline indicates the normal sea ice extent (1971–2000).

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Figure 11 Interannual variations in the maximum sea ice extent (red lines) and accumulated sea ice extent (green lines) in the Sea of
Okhotsk from 1971 to 2008
Accumulated sea ice extent: the sum of all fiveday sea ice extent values from December of theprevious year to May.

Atmospheric Circulation Anomalies behind US Midwest Flooding in
June 2008
Introduction
Severe storms battered the Midwest of the USA in early
June.
According to surface synoptic observations(SYNOP), 10-day precipitation amounts from 1 to 10 Junereached 100–230 mm (Figure 12) in the Midwest, a level 3–
11 times heavier than the average monthly precipitation.
The heavy rainfall and resulting floods along the Mississippi caused serious damage to social and agricultural properties, especially in Iowa and Wisconsin. Summarized below are the characteristics of the large-scale atmosphericcirculation anomalies behind the heavy rainfall of early
June 2008.
Upper troposphere circulation
Figure 13 shows 250-hPa-level geopotential heights andtheir anomalies, along with wave activity fluxes derived
from 10-day mean height anomalies from 1 to 10 June
2008. Wave activity fluxes indicate the group velocity of a
Rossby wave, and are a useful diagnostic tool in illustrating
the energy propagation of such waves (Takaya and Nakamura, 2001). In the upper troposphere, a trough in thewestern US and a ridge in the eastern US developed in association with the energy propagation of a quasi-stationary
Rossby wave. This trough involved upper-troposphericcold air.
The upper-tropospheric jet stream was much stronger

than normal from the northeastern Pacific to the western US(Figure 14). In the western US, the jet stream was displaced well south of its normal position due to a developed
upper trough. The southwesterly jet over the Midwest suggests that upward motion could have occurred in this area.
The strong vertical shear of westerly winds observed in thewestern US may have represented a favorable atmosphericcondition for the development of baroclinic disturbances.
In June, synoptic disturbance activity was enhanced fromthe northeastern Pacific to the Midwest (not shown in the
figures).

Figure 13 Ten-day mean 250-hPa geopotential heights(contours, unit: m) and their anomalies (colored areas, unit:m), and wave activity fluxes (vectors, unit: m2/s2) from 1 to 10
June 2008

Figure 12 Ten-day precipitation amounts in North America
from 1 to 10 June 2008
Precipitation amounts are based on surface synoptic observations(SYNOP).

Figure 14 Ten-day mean 200-hPa wind (vectors) and zonal
wind speeds (colored areas, unit: m/s) from 1 to 10 June 2008
Gray contours indicate the climatological mean of 200-hPa zonal
wind speeds in the same period (unit: m/s).

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No. 13 | SummerLower troposphere circulation
In the lower troposphere, southwesterly winds werestronger than normal from the Bay of Mexico to the Midwest along the edge of the Atlantic subtropical highpressure system. This flow led to warm air advection in theeastern US (not shown in the figures). A frontal zone in thelower troposphere formed around the Midwest between thiswarm air mass and a cold air mass in the western US withthe upper cold trough mentioned above.
Moreover, the flow from the Bay of Mexico induced
anomalous water vapor fluxes. Figure 15 illustrates water
vapor fluxes and their divergence at 850-hPa level in early
June. The panel on the left shows the 10-day average from
1 to 10 June 2008, while that on the right shows flux deviations and divergence from the normal in the same period.
These panels reveal that northward/northeastward water
vapor fluxes from the coastal area to the central US werestronger than normal in the lower troposphere. This large
flow of atmospheric moisture moved from the Bay of Mexico into the central and eastern US, and a strong convergence of the water vapor fluxes was observed in the Midwest. This excessive supply of water vapor to the Midwest
may have been one of the major contributing factors to theheavy rainfall in the area.
Possible effect of SST anomalies
Similar characteristics of atmospheric circulation were
found in the case of the Great Flood of summer 1993
(Trenberth and Guillemot, 1996). In that year, sea surface
temperature (SST) anomalies in the tropical Pacific showed
an El Niño-like structure, while in June 2008 they had a La
Niña-like structure. In late May 2008, however, positive
SST anomalies were observed around the eastern tropical
Pacific and the Caribbean Sea where convective activities
were enhanced. The warm SST and active convection may

have played an important role in supplying water vapor to
the atmosphere in and around the Bay of Mexico.
Summary
From the diagnostic analysis described above, many contributing factors to the heavy rainfall in the Midwest were
found in early June. The major influences that may haveinduced this rainfall are summarized in the schematic diagram in Figure 16. First, an upper-tropospheric trough andan associated southwardly-shifted jet stream created favorable atmospheric conditions for the development of disturbances. These upper-atmospheric conditions persisted during early June in association with the energy propagation ofa quasi-stationary Rossby wave. Secondly, warm and moist
air flowing along the edge of the Atlantic subtropical highpressure system formed a strong frontal zone in the lower
troposphere and led to an excessive supply of water vapor
and its convergence in the Midwest. This may have been
one of the major contributing factors to the heavy rainfall inthis area. Lastly, warm SST anomalies from the eastern
tropical Pacific to the Caribbean Sea and enhanced convective activities may have played a role in supplying water
vapor to the atmosphere.
References
Trenberth, K. E., and C. J. Guillemot, 1996: Physical processes involved in the 1988 drought and 1993 flood in North
America. J. Clim., 9, 1288-1298.
Takaya, K., and H. Nakamura, 2001: A formation of aphase-independent wave-activity flux for stationary andmigratory quasigeostrophic eddies on a zonally varying
basic flow. J. Atmos. Sci., 58, 608-627.
(Atsushi Goto, Climate Prediction Division)

Figure 15 Ten-day mean water vapor
fluxes (vectors, unit: kg/kg·m/s) andtheir divergence (colored areas, unit:
10-8kg/kg/s) at 850-hPa level from 1 to
10 June 2008 (left); the panel on theright shows the same situation as theone on the left, but for deviations fromtheir climatological means in the same
period.

Figure 16 Schematic diagram of atmosphericcirculation anomalies observed in early June
This shows possible factors contributing to theheavy rainfall in the Midwest.

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WMO Working Group on Climate-Related Matters for Regional Association
II (WGCRM RA II)
JMA. He recalled that significant progress has been madein climate-related activities in RA II, particularly in the development of the Regional Climate Center (RCC) Network’s activities.
The meeting reviewed the implementation of climaterelated activities in RA II including the development of the
RCC Network in the region. The meeting also considered
future plans for the RCC Network and agreed to further
develop cooperative relationship among Members.
A report of the meeting will be submitted to the President of RA II by the Chair of the WGCRM.

A meeting of the Working Group on Climate-Related
Matters (WGCRM) for Regional Association II (RA II) of
the World Meteorological Organization (WMO) took placeat the Japan Meteorological Agency (JMA) headquarters inTokyo, Japan, from 7–8 August 2008. The meeting wasattended by seven members of the Working Group from
China, India, the Islamic Republic of Iran, Japan, the Republic of Korea and the Russian Federation, and two fromthe WMO Secretariat. As Dr. Zheng Guoguang, Chair of
the WGCRM, was unable to attend the meeting, it waschaired by Dr. Koichi Kurihara of JMA, Vice-Chair of the
WGCRM, at the Chair’s request.
At the opening ceremony, Dr. Tetsu Hiraki, DirectorGeneral of JMA, welcomed the participants on behalf of(Kumi Hayashi, Climate Prediction Division)

Hands-on Training for Climate Data Communication and Applications
at TCC
JMA’s Tokyo Climate Center (TCC) ran a hands-on
training course on climate data communication and applications from 13 July to 2 August 2008 at the request of the
Malaysian Meteorological Department (MMD). The threeweek course was attended by Mr. Mohd Sani Bin Saayon
and Ms. Nik Noorhayati Binti Nik Abdul Majid from the
Climate Section of MMD.
In the training, the participants learned the use of Linuxmachines, data processing for GRIB and GRIB2 and visualization of climate-related data and products.
Another hands-on training course for climate forecastingand its applications will be held in September this year withthe participation of another two officers from MMD.
(Kumi Hayashi, Climate Prediction Division)
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
TCC website: http://ds.data.jma.go.jp/tcc/tcc/index.html
to: tcc@climar.kishou.go.jp(Chief Editor: Kumi Hayashi)Tokyo Climate Center

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