Autumn 2010

No. 22
Contents
El Niño Outlook (October 2010 – April 2011)

1

JMA’s Seasonal Numerical Ensemble Prediction for Winter 2010/2011

2

ColdCold-season Outlook for Winter 2010/2011 in Japan

4

Summary of the 2010 Asian Summer Monsoon

6

Status of the Antarctic Ozone Hole in 2010

8

Primary Factors Contributing to Japan’s Extremely Hot Summer of 20108

El Niño Outlook (October 2010 – April 2011)
La Niña conditions are present in the equatorial Pacific,
and are likely to persist into boreal winter.
Pacific Ocean
In September 2010, the SST deviation from a sliding
30-year mean SST averaged over the NINO.3 region (5˚N
– 5˚S, 150˚W – 90˚W) was -1.3°C. The five-month running-mean value of NINO.3 SST deviations was -0.8°C for
July, and the Southern Oscillation Index for September was+2.3. In September, negative SST anomalies prevailed
over most of the equatorial Pacific except near Indonesia,
where positive values were recorded (Figures 1 (b) and 3(a)). Subsurface temperature anomalies were positive inthe western equatorial Pacific, and were remarkably negative in its central and eastern parts (Figures 2 (b) and 3(b)). In the equatorial Pacific, convective activity near thedate line was calmer than normal. Easterly wind anomalies in the lower troposphere prevailed in the western andcentral equatorial Pacific. These oceanic and atmosphericconditions are consistent with those seen during La Niña
events.
In the equatorial Pacific, persistent easterly anomalies
in the lower troposphere brought continued negative subsurface temperature anomalies in its central and easternparts. These negative anomalies will in turn cause SSTs toremain below normal.
According to JMA's El Niño prediction model, NINO.3
SST deviations will continue to be below normal into boreal winter (Figure 4).

(a)

(a)

(b)

(b)

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

Figure 1 Monthly mean (a) sea surface temperatures (SSTs)and (b) SST anomalies in the Indian and Pacific Ocean areasfor September 2010
Contour intervals are 1˚C in (a) and 0.5˚C in (b). The base period for the normal is 1971 – 2000.

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No. 22 | Autumn 2010

(a)

(b)

Figure 3 Time-longitude cross sections of (a) SST and (b) ocean heat content (OHC) anomalies along
the equator in the Indian and Pacific Ocean areas
OHCs are defined here as vertical averaged temperatures in the top 300 m. The base periods for the normal
are 1971 – 2000 for (a) and 1979 – 2004 for (b).

Considering all the above observations and model result,it can be concluded that La Niña conditions are present in
the equatorial Pacific and are likely to persist into boreal
winter.
It is likely that the SST averaged over the NINO.WEST
region (Eq. – 15°N, 130°E – 150°E) will continue to be nearor above normal into boreal winter.
Indian Ocean
The SST averaged over the tropical Indian Ocean(IOBW) region (20°S – 20°N, 40°E – 100°E) has been nearnormal since August. It is likely to gradually become below
normal in the months ahead.
Figure 4 Outlook of NINO.3 SST deviation produced by
the El Niño prediction modelThis figure shows a time series of monthly NINO.3 SST deviations. The thick line with closed circles shows observed
SST deviations, and the boxes show the values produced forthe next six months by the El Niño prediction model. Eachbox denotes the range into which the SST deviation is expected to fall with a probability of 70%.

Impact on the global climate
In September, conditions were much warmer than normal
in East Asia and over the islands to the east of Australia.
This was consistent with common climate patterns seen inpast La Niña events.
(Ichiro Ishikawa, Climate Prediction Division)* The SST normals for the NINO.WEST region (Eq. – 15°
N, 130°E – 150°E) and the IOBW region (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 oflong-term trends.

JMA’s Seasonal Numerical Ensemble Prediction for Winter 2010/2011
1. Introduction
This article outlines JMA’s dynamical seasonal ensemble prediction for winter 2010/2011 (December 2010 – February 2011, referred to as DJF), which was used as a basis
for the Agency’s operational cold-season outlook issued on
25 October, 2010. The prediction shown here is based on
the seasonal ensemble prediction system with the Atmosphere-Ocean General Circulation Model (AOGCM). Pleaserefer to the column for details of this system.
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 mid- and highlatitudes of the Northern Hemisphere are explained in Section 4.

According to JMA’s seasonal ensemble prediction system,a negative anomaly in the central and eastern equatorial Pacific is expected to continue in winter 2010/2011, indicatingthat the current La Niña event is likely to persist during thisperiod. Corresponding to sea surface temperature (SST)
conditions, the JMA system indicates active rainfall aroundthe Maritime Continent, the South Pacific Convergence Zone
(SPCZ) and the eastern tropical Indian Ocean, and suppressed rainfall in the central part of the tropical Pacific.
Below-normal surface temperatures are expected around theeastern part of China and over Southeast Asia, while abovenormal temperatures are expected in northern Japan.

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2. SST anomalies (Figure 5)
In September 2010, remarkably negative andpositive SST anomalies were seen in the central
to eastern equatorial Pacific and western tropical
Pacific, respectively. These conditions indicatethat the current La Niña event, which appearedin the summer of 2010, is well developed. According to JMA’s El Niño outlook, the La Niña
event is expected to continue into winter (seealso JMA’s El Niño Outlook in this issue).
The predicted SST anomalies are shown in
Figure 5. Below-normal SSTs are predicted incentral to eastern parts of the equatorial Pacific,
while above-normal SSTs are predicted in thewestern tropical Pacific and the tropical Atlantic.

Figure 5 Predicted SST (contours) and SST anomalies (shading) for
December 2010 – February 2011 (ensemble mean of 51 members)

3. Prediction in the tropics and sub-tropics (Figure 6)
Predicted precipitation shows conditions typical of
those seen during La Niña events. Below-normal precipitation is predicted in the central equatorial Pacific, while
above-normal precipitation is predicted over the eastern
Indian Ocean, the Maritime Continent and the South Pacific Convergence Zone (SPCZ).
In the upper troposphere, a negative velocity potential
anomaly at 200 hPa (i.e., more divergent) is predicted over
the Maritime Continent, reflecting active precipitation in
the region, while positive (i.e., more convergent) anoma-lies are predicted from the central part of the tropical Pacific and the western part of the Indian Ocean. The predicted stream function at 200 hPa shows an anti-cyclonicanomaly over Southeast Asia and a cyclonic anomaly inthe northeast tropical Pacific associated with the precipitation anomalies. In the lower troposphere, a cyclonic anomaly is predicted over the northeastern part of the Indian
Ocean, while an anti-cyclonic anomaly is expected in thenorthwestern part of the tropical Pacific. These features
are consistent with those seen during La Niña events.

Figure 6 Predicted atmospheric fields from 60°N – 60°S for December 2010 – February 2011 (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 (shading). 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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4. Prediction in the mid- and high latitudes of the Northern Hemisphere (Figures 7 and 8)
The seasonal ensemble system predicts positive 500-hPa
geopotential height anomalies over the North Pacific andnegative anomalies from the eastern and southern part ofJapan to the western part of Northeast Asia. Below-normal
surface temperatures are expected around East and South-

east Asia, while above-normal temperatures are expected innorthern Japan.
(Yuhei Takaya, Climate Prediction Division)

Figure 7 Predicted atmospheric fields from 60°N – 60°S for December 2010 – February 2011 (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.

Figures 8 Predicted surface (2-m) temperatures for
December 2010 – February 2011 (ensemble mean of
51 members)
The contour interval is 2 degrees. The shading indicates 2-m temperature anomaly.

JMA’s Seasonal Ensemble Prediction System
JMA operates a seasonal Ensemble Prediction System (EPS) using the Atmosphere-Ocean General Circulation
Model (AOGCM) to make seasonal predictions beyond a one-month time range. The EPS produces perturbed
initial conditions by means of a combination of the initial perturbation method and the lagged average forecasting (LAF) method. The prediction consists of 51 members from the latest six initial dates (9 members are run
every five days). Details of the prediction system and verification maps based on 30-year hindcast experiments(1979 – 2008) are available at http://ds.data.jma.go.jp/tcc/tcc/products/model/.

Cold-season Outlook for Winter 2010/2011 in Japan
JMA’s seasonal forecast for winter 2010/2011, issued on
22 September 2010, indicates no significant temperature
anomalies for any part of Japan.
1. Oceanic conditions
In August 2010, the SST deviation from a sliding 30year mean SST averaged over the NINO.3 region was -1.0°
C. The five-month running-mean value of NINO.3 SST
deviations was -0.4°C for June, and the Southern Oscillation Index for August was +1.9. In August, remarkably
positive SST anomalies were seen in the western equatorial
Pacific, and remarkably negative anomalies were foundfrom the area west of the date line to eastern parts. Subsurface temperature anomalies were positive in the westernequatorial Pacific, and were remarkably negative in its central and eastern parts. In the equatorial Pacific, convective

Figure 9 Outlook for winter 2010/2011 temperature probability in JapanTokyo Climate Center4

No. 22 | Autumn 2010

activity near the date line was calmer than normal. Easterly
wind anomalies in the lower troposphere prevailed in thewestern and central equatorial Pacific. These oceanic andatmospheric conditions are consistent with those seen during La Niña events. In the equatorial Pacific, persistenteasterly anomalies in the lower troposphere brought continued negative subsurface temperature anomalies in its central and eastern parts. These negative anomalies will in turncause SSTs to remain below normal. According to JMA’s
couple-model, NINO.3 SST deviations will continue to be
below normal into boreal winter (December-JanuaryFebruary).
Considering all the above observations, it can be concluded that La Niña conditions are present in the equatorial
Pacific and are likely to persist into boreal winter. It is
likely that the SST averaged over the NINO.WEST region
will continue to be near or above normal from boreal autumn to winter.
2. Numerical prediction
The SST anomaly pattern predicted by the JMA couplemodel is very similar to that seen during La Niña events(i.e., above normal in the western Pacific and below normal
in the central and eastern Pacific).
In association with this pattern, the ensemble averaged
atmospheric circulation anomaly pattern predicted by themodel is also very similar to that seen during La Niña
events in the tropics and the sub-tropics as outlined below.
In the lower tropospheric (850 hPa) stream function
field, cyclonic circulation anomaly is clearly predicted fromsouthern India to the South China Sea. In the upper tropospheric (200 hPa) stream function field, anti-cyclonic circulation anomaly is clearly predicted from northern India tosouthern China, and cyclonic circulation anomaly is predicted around Japan. Corresponding to the circulation
anomalies over East Asia, the subtropical jet streams will
shift northward over China and southward over Japan, suggesting a strong winter monsoon around the latter. This
meandering of the subtropical jet streams is expected as aresult of the predicted La Niña-type SST anomalies.
In the mid- and high latitudes, a slightly positive phaseof the Arctic Oscillation (AO) is predicted by the JMA couple-model. The positive (negative) phase of the AO tends

to cause a weak (strong) winter monsoon and above-normal(below-normal) temperatures in northern Japan. However,the spread among each ensemble member is large, and thehindcast (30 years from 1979 to 2008) suggests that themodel does not have a level of skill sufficient to predict the
AO.
3. Long-term trends and decadal variation
Long-term upward trends are clearly seen in wintermean temperatures over Japan except in its northern part,
where the winter mean temperature shows large year-toyear fluctuations and recent ten-winter mean temperatures
have been near normal (although slightly warmer). Winterprecipitation has tended to be above normal on the Pacificside of northern, eastern and western Japan since the end of
the 1990s.
The tropospheric thickness temperature averaged overthe mid-latitudes of the Northern Hemisphere (30°N – 50°N), which is positively correlated with temperatures in Japan, has tended to be above normal since 2006. According
to the JMA couple-model, it will remain above normal into
boreal winter (December-January-February).
4. Conclusion
According to numerical prediction, below-normal temperatures are expected for Japan in winter (except in its
northern part) in response to La Niña conditions. However,considering the long-term trend, the temperature is in fact
likely to be higher than the results of numerical prediction
suggest. In northern Japan, both numerical prediction andthe long-term trend suggest the likelihood that temperatures
will be slightly higher than normal in winter.
5. Outlook summary
Predicted cold-season mean temperatures and total precipitation amounts show no significant anomalies for any
part of Japan. Cold-season snowfall amounts on the Sea ofJapan side of the country are expected to be near or below
normal with a 40% probability for each in northern Japan(Figures 9, 10 and 11).
(Hajime Takayama, Climate Prediction Division)

Figure 10 Outlook for winter 2010/2011 precipitation probability in Japan

Figure 11 Outlook for winter 2010/2011 snowfall probability
in JapanTokyo Climate Center5

No. 22 | Autumn 2010

Summary of the 2010 Asian Summer Monsoon
1. Monsoon activity and atmospheric circulation
Convective activity (inferred from the seasonal mean(i.e., that from June to September) of outgoing longwave
radiation (OLR)) associated with the Asian summer monsoon was enhanced across a broad area including the Maritime Continent, the Arabian Sea, Pakistan, the South China
Sea and the area to the north of the Philippines (Figure 12).
In the period from June to the first half of July, however, it
was suppressed from northern India to the Indochina Peninsula and to the east of the Philippines. Across the westernand central equatorial Pacific, suppressed convection wasseen from June 2010.
In the lower troposphere, monsoon westerlies werestronger than normal over the Arabian Sea, and were
weaker than normal in the Bay of Bengal and over theSouth China Sea (Figure 13 (b)). The monsoon trougharound the Philippines was weaker than normal. Anticyclonic circulation anomalies were prominent over a wide
area from the North Pacific and East Asia to northern India.
In the upper troposphere, the Tibetan High was extended
northeastward and westward from its normal position(Figure 13 (a)). In the equatorial region, easterly wind
anomalies were predominant over the Indian Ocean, while
westerly anomalies were seen over the western and central
Pacific.
The active phase of the Madden-Julian Oscillation(MJO) propagated eastward with a period of approximately
30 days (Figure 14). The area of active convection originally enhanced by the MJO to the south of India was seen
to propagate northward around India (Figure 15).
(Shotaro Tanaka, Climate Prediction Division)
Figure 12 Four-month mean outgoing longwave radiation(OLR) and its anomaly for June – September 2010
The contours indicate OLR (W/m2) at intervals of 10 W/m2,
and the color shading denotes OLR anomalies from the 1979 –2004 average.

Figure 13 Four-month mean stream function and its anomaly for June – September 2010(a) The contours indicate 200-hPa stream function (m2/s) at intervals of 10 × 106 m2/s, and the color shading indicates 200-hPa
stream function anomalies from the 1979 – 2004 average. (b) The contours indicate 850-hPa stream function (m2/s) at intervalsof 2.5 × 106 m2/s, and the color shading indicates 850-hPa stream function anomalies from the 1979 – 2004 average.

Figure 14 Time-longitude cross section of five-day
mean OLR anomaly from June to September 2010 (5ºS
– 5ºN mean)
The shading denotes OLR anomalies (W/m2) from the 1979
– 2004 average. Cold and warm shading indicates abovenormal and below-normal convective activity, respectively.

Tokyo Climate Center

Figure 15 Latitude-time cross section of five-day mean OLR
from April to September 2010 ((a) India (65 – 85ºE mean), (b)area east of the Philippines (125 – 145ºE mean))
The thick black lines indicate the climatological mean OLR for
the period from 1979 to 2004. The shading denotes the OLR in2010 (W/m2).

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2. Precipitation and temperature
Four-month total precipitation amounts based on
CLIMAT reports during the monsoon season (June –September) were above 200% of the normal aroundPakistan and in southern Indonesia, and were below
60% of the normal around Mongolia (Figure 16).
They were mostly consistent with the distribution of
OLR anomalies (Figure 12).
Four-month mean temperatures for the same period
were higher than normal over most of eastern to southern Asia except around northern Pakistan and midsouthern China (Figure 17).
Extremely heavy precipitation was observed aroundPakistan throughout the season. In contrast, extremely
light precipitation was observed from the southern partof eastern Siberia to northern China in June andaround Mongolia in July (figures not shown).
Monthly mean temperatures were extremely high inmany regions throughout the period. The seasonalmean temperature in Japan for summer (i.e., the threemonth period from June to August) was the highest
since JMA’s records began in 1898.
It was reported that heavy rains in Pakistan from 28
July to 7 August triggered floods in several parts of thecountry, resulting in 1,961 fatalities. It was also reported that a mudslide caused 1,765 fatalities in central
China (Zhouqu County in Gansu Province) on 7 – 8August.
3. Tropical cyclones
During the monsoon season, 11 tropical cyclones(TCs) of tropical storm (TS) intensity or higher formed
over the western North Pacific (Figure 16 and Table1). The number of formations was much lower than
the 1971 – 2000 average of 16.4. A total of 7 among
these 11 passed around the South China Sea and approached or hit southern China or Vietnam. Two TCs
hit the main islands of Japan.
In July, Typhoon Conson caused 196 fatalities in
the Philippines. In September, Typhoon Kompasu
caused 12 fatalities in the Republic of Korea and 20 in
the Democratic People's Republic of Korea.
Note: Disaster details are based on informationfrom the UN’s EM-DAT disaster database.
(Takafumi Umeda, Climate Prediction Division)

Figure 16 Four-month precipitation ratio (%) and tropical
cyclone tracks in the northwestern Pacific from June to September 2010

Figure 17 Four-month mean temperature anomaly (°C) from
June to September 2010
Table 1 Tropical cyclones forming over the western North Pacific from June to September 2010
MaximumID
Date
CateNameWinds2)
number(UTC)
gory1)(Knots)T1002

Conson7/12 – 7/17

TY

70

T1003

Chanthu

7/19 – 7/23

TY

70

T1004

Dianmu8/8 – 8/12

STS

50

T1005

Mindulle

8/23 – 8/24

TS

45

T1006

Lionrock

8/28 – 9/2

STS

50

T1007

Kompasu

8/29 – 9/2

TY

80

T1008

Namtheun

8/30 – 8/31

TS

35

T1009

Malou

9/4 – 9/8

STS

50

T1010

Meranti

9/9 – 9/10

TS

45

T1011

Fanapi9/15 – 9/20

TY

95

T1012

Malakas9/21 – 9/25

TY

75

Note: Prepared by the RSMC Typhoon Center (provisional data
for T1010 – T1012)
1) Intensity classification for tropical cyclones
TS: Tropical Storm
STS: Severe Tropical Storm
TY: Typhoon2) Estimated maximum 10-minute mean windTokyo Climate Center

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Status of the Antarctic Ozone Hole in 2010
The Antarctic ozone hole in 2010 covered its third-smallest
area since 1990.
The Antarctic ozone hole has appeared for the last 30
years from late winter to early spring (August – December),peaking in September or early October. It is defined as thearea where the total ozone column is equal to or less than
220 m atm-cm.
According to JMA’s analysis of Aura OMI data, theozone hole in 2010 appeared in August and expanded toreach a maximum area of 21.9 million km2 on 25 September. This was 1.6 times as large as the Antarctic Continent(Figure 18), and represented its third-smallest area since1990 after 1990 and 2002. The five spherical images in
Figure 18 indicate total ozone column distributions in theSouthern Hemisphere with the ozone hole shown in gray.
The Antarctic ozone hole is expected to return to pre1980 levels in the late 21st century according to WMO/UNEP Scientific Assessment of Ozone Depletion: 2010.
Continued close observation of the ozone layer is necessary
to allow assessment of the hole’s shrinkage.
(Seiji Miyauchi, Ozone Layer Monitoring Office,Atmospheric Environment Division)

Figure 18 Daily changes in the area of the Antarctic ozone hole in 2010 (upper left), changes in its annual maximum area since
1979 (upper right), and total ozone distributions in the Southern Hemisphere on the indicated dates (bottom)
The Antarctic ozone hole is shown in gray in the spherical images at the bottom. These figures were made from Aura OMI data produced by KNMI (the Royal Netherlands Meteorological Institute) and processed using the ozone retrieval algorithm of NASA (the National Aeronautics and Space Administration).

Primary Factors Contributing to Japan’s Extremely Hot Summer of 2010
In summer (June – August) 2010, Japan experienced nationwide record-breaking high temperatures. Shortly after
this period on 3 September, JMA organized an extraordinary
meeting of the Advisory Panel on Extreme Climate Events1 toidentify the characteristic atmospheric circulations causing

these extremely hot conditions and to investigate the factors
contributing to them. This report summarizes the atmospheric features and possible influences identified by the Advisory Panel as main background factors to Japan’s hottest
summer on record.

1
The Advisory Panel, consisting of prominent experts on climate
science from universities and research institutes, was establishedin June 2007 by JMA to investigate extreme climate events basedon the latest knowledge and findings.

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No. 22 | Autumn 2010

1. Temperature for summer 2010 in JapanThe seasonal mean temperature in Japan forsummer 2010 (i.e., the three-month period from
June to August) ousted that of summer 1994
from the top spot as the highest since JMA’s
records began in 1898, with a deviation2 of+1.64°C from the 1971 – 2000 average (Figure19). The temperature anomalies for the individual months were the fifth highest on record at+1.24°C for June, the eleventh highest at +1.42°
C for July, and the highest at +2.25°C for August. In most regions of Japan, above-normal
temperatures persisted during the summer.
2. Oceanographic conditions and convective
activity in the tropics
In summer (June – August) 2010, a La Niña
event followed the El Niño period that started insummer 2009 and ended in spring (March –May) 2010 (Figure 20). Sea surface temperatures (SSTs) were above normal in the Indian
Ocean and the tropical Atlantic. This 2010 pattern echoed those of the La Niña events seen in
1988 and 1998 that rapidly occurred in springand summer, respectively, after the end of an El
Niño period in the previous season (Figure 21).
Convective activity (inferred from outgoing
longwave radiation (OLR)) associated with the
Asian summer monsoon was suppressed acrossa broad area from northern India to the Indochina Peninsula and to the east of the Philippines in the first half of summer 2010, and wasenhanced in the Arabian Sea and from the Indochina Peninsula to the north of the Philippines inthe second half (Figure 22). In the eastern Indian Ocean and on the Maritime Continent, convective activity was enhanced throughout thesummer.

Figure 19 Long-term change in seasonal temperature anomalies forsummer (June – August) in Japan
Anomalies are calculated as the average of temperature deviations fromthe 1971 – 2000 normal at the 17 observation stations2. The bars indicate
anomalies of temperature for each summer. The blue line indicates the
five-year running mean, and the red line shows the long-term linear
trend.
Mar. – May 2010

Jun. – Aug. 2010

Figure 20 Three-month mean sea surface temperature anomalies
for March – May (upper) and June – August (lower) 2010
The normal is the 1971 – 2000 average. The analysis data are COBESST.

Figure 21 Time series of five-month running mean sea surface
temperature deviations from the climatological mean based on asliding 30-year period for NINO.3 (5˚S – 5˚N, 150˚W – 90˚W)

2

Observatory stations representing the average temperatureof Japan are selected from those deemed to be least influenced by the urban heat island phenomenon.

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1 Jun. – 15 Jul. 201016 Jul. – 31 Aug. 2010

Figure 22 Outgoing Longwave Radiation (OLR) anomalies (unit: W/m2)
Panels on the left: Cold and warm shading indicates enhanced and suppressed convective activity, respectively, in comparison with the normal (i.e., the 1979 – 2004 average). Panels on the right: Values indicate zonally averaged (60˚E –140˚E) OLR anomalies in the corresponding panels on the left. Data provided by NOAA.

3. Characteristic atmospheric circulation causing
Japan’s hot summer and related factors(1) Tropospheric air temperature
The zonally averaged tropospheric air temperaturein the mid-latitudes of the Northern Hemisphere was
the highest in summer (June – August) since 1979
(Figure 23). As shown in Figure 24, the values for1998 and 1988 were the second and fourth highest,
respectively, since 1979. Zonally averaged tropospheric thickness in the tropics reached an abovenormal level in July 2009 and matured in the first halfof 2010 (left panel of Figure 24). In June 2010, thethickness in the tropics remained above normal but
decreased, while that in the mid-latitudes of the Northern Hemisphere rapidly increased and remained significantly above normal throughout the summer. Similar
thickness anomaly evolution was identified in 1988 and1998 (central and right panels of Figure 24).
As research so far (e.g., Angell, 1990) has indicated,
tropospheric air temperatures increase on a global scale
after El Niño events and then remain higher than normal for several months. Examination of past La Niña
events shows a tendency for higher-than-normal tropospheric air temperatures in the mid-latitudes of theNorthern Hemisphere, while those in the tropics havebeen below normal during summers with a La Niña
event. This is consistent with the results of previous
research (e.g., Seager et al., 2003).
It is therefore possible that zonally averaged tropospheric air temperatures in the mid-latitudes of theTokyo Climate Center

Figure 23 Time series of three-month (June – August) zonallyaveraged temperature anomalies (unit: K) in the mid-latitudes(30˚N – 60˚N) of the Northern Hemisphere calculated fromthickness (850 – 300 hPa)
The base period for the normal is 1979 – 2004. The analysis data
are JRA-25/JCDAS.

Northern Hemisphere were extremely high in summer 2010
from the influence of the El Niño event and partly due tothe effects of the La Niña event.
A warming trend can be identified in the zonally averaged tropospheric air temperature in the mid-latitudes of theNorthern Hemisphere (Figure 23). This trend may be associated with global warming due to the buildup of anthropogenic greenhouse gases.

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Jan. 2009 – Aug. 2010

Jan. 1987 – Dec. 1988

Jan. 1997 – Dec. 1998

Figure 24 Time-latitude cross section of monthly, zonally averaged thickness anomaly (unit: m)
The base period for the normal is 1979 – 2004. The analysis data are JRA-25/JCDAS.

(2) Remarkably strong anticyclone over JapanThe subtropical jet stream in the vicinity of Japan
showed a southward-shifted tendency from its normal position in the first half of summer 2010, while
the jet stream shifted northward from its normal position with a frequent northward meander (a ridge ofhigh pressure) in the second half (Figure 25). Corresponding to the features of the subtropical jet stream,
the extension of the Tibetan High to Japan was
weaker than normal in the first half of summer 2010,
while it was stronger than normal and equivalentbarotropic highs developed and persisted over Japanin the second half (Figures 26 and 27).
As detailed in Section 2, convective activity wasbroadly enhanced in and around the Indian Ocean in
the second half of summer 2010 (Figure 22). Considering that research so far (e.g., Krishnan andSugi, 2001; Enomoto, 2004) indicates a link between
the Asian summer monsoon and Japan’s climate,statistical analysis was implemented to examine therelationship between convective activity linked to

Figure 25 Latitude-time cross section of normals (black lines)
and anomalies (colored shading) of the 200-hPa zonal wind speed
averaged in the vicinity of Japan (125˚E – 145˚E)
The base period for the normal is 1979 – 2004. The analysis data are
JRA-25/JCDAS.

June 2010

August 2010

Figure 26 Monthly-mean 200-hPa stream function and anomaly
The contours show the stream function at intervals of 1 x 107 m2/s, and the shading indicates stream function anomalies. In
the Northern (Southern) Hemisphere, warm (cold) colored shading denotes anticyclonic (cyclonic) circulation anomalies.
The base period for the normal is 1979 – 2004. The analysis data are JRA-25/JCDAS.

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200-hPa height and anomaly

500-hPa height and anomaly

Sea level pressure and anomaly

Figure 27 Monthly-mean atmospheric circulation around Japan (August 2010)
Panel on the left: The contours indicate 200-hPa height at intervals of 120 m. Central panel: The contours indicate
500-hPa height at intervals of 60 m. Panel on the right: The contours indicate sea level pressure at intervals of 4-hPa.
The shading shows their anomalies. The base period for the normal is 1979 – 2004. The analysis data are JRA-25/
JCDAS.

the Asian summer monsoon and the subtropical jet stream
in the vicinity of Japan (Figure 28). The results indicatedthat when convective activity is enhanced (or suppressed)
over the region from the northern Indian Ocean to thenortheast of the Philippines (10˚N – 20˚N, 60˚E – 140˚E),
the subtropical jet stream near Japan tends to shift northward (or southward) from its normal position. Furthermore, a similar statistical examination was implemented inwhich the region for averaging convective activity was
expanded to a wider area in and around the tropical Indian
Ocean and the Maritime Continent (10˚S – 20˚N, 60˚E –140˚E). The results showed that when convective activity
is enhanced over this wider area, the subtropical jet stream
near Japan tends to shift northward from its normal posi-tion (figure not shown).
It therefore seems that the northward shift of the subtropical jet in the vicinity of Japan was associated withactive convections over the broad region in and around theIndian Ocean. In addition, considering previous studies(e.g., Nitta, 1987) indicating the influence of convective
activity around the Philippines on Japan, active convections from the northern South China Sea to the area to thenortheast of the Philippines may have been partly responsible for the strength of anticyclones around Japan, especially from the second half of August to early September.

Figure 28 Linear regression coefficients of 200-hPa zonal wind speed onto area-averaged convective activity(OLR) over the region from the northern Indian Ocean to the area to the northeast of the Philippines (10˚N –20˚N, 60˚E – 140˚E) for July and August
The panel on the left indicates that when convective activity was enhanced (suppressed) over the region, the subtropical jet stream was stronger (weaker) than normal in the cold (warm) colored shading. Panel on the right: theshading shows a 95% confidence level based on F-testing. The base period for the statistical analysis is 1979 –2009. The analysis data are JRA-25/JCDAS.

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(3) Okhotsk HighThe Okhotsk High (a cool semi-stationary anticyclone)often develops around the Sea of Okhotsk from spring toautumn and occasionally brings cool air to the Pacific sideof northern and eastern Japan, resulting in cool summers. A
blocking high in the upper troposphere over the Sea of Okhotsk plays an integral role in the formation of the Okhotsk
High (Nakamura and Fukamachi, 2004). In July 2003, in
association with the development of an upper-level blocking high over the Sea of Okhotsk, the Okhotsk High appeared and persisted throughout the month, bringing aboutsignificantly below-normal temperatures in northern andeastern Japan (the panels on the right of Figure 29).
In June 2010, warm anticyclones frequently covered Japan, particularly its northern parts (the panels on the left of
Figure 29). As a result, temperatures were above normal
across most of the country. In the period from June to thefirst half of July, the Okhotsk High was less developed thisyear than in past years (Figure 30). In the second half ofJuly, the phenomenon temporarily appeared but influenced
Japan little due to the northward shift of the subtropical jet
near the country and the strong Pacific High to its east(central panels of Figure 29).

Z500 (June 2010)

Z500 (July 2010)

Z500 (July 2003)

SLP (June 2010)

SLP (July 2010)

SLP (July 2003)

Figure 29 Monthly-mean atmospheric circulation around Japan (left: June 2010; center: July 2010; right:
July 2003)
Upper panels: monthly-mean 500-hPa height (thick black contours) at intervals of 60 m and anomaly (shading)
Lower panels: monthly-mean sea level pressure (thick black contours) at intervals of 4 hPa and anomaly (shading)
The base period for the normal is 1979 – 2004. The analysis data are JRA-25/JCDAS.

Figure 30 Time series of Okhotsk High Index (2001 – 2010)
The index is the average of sea level pressure anomalies over the Sea of Okhotsk (45˚N – 60˚N, 140˚E – 155˚E).
The red lines indicate progression of 2010. The base period for the normal is 1979 – 2004. The analysis data are
JRA-25/JCDAS.

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4. Conclusion and discussion
The Advisory Panel on Extreme Climate Events identified three atmospheric circulation features related to Japan’s extremely hot summer of 2010:(1) The zonally averaged tropospheric air temperature in
the mid-latitudes of the Northern Hemisphere was thehighest for June – August since 1979
(2) A remarkably strong anticyclone persisted over Japan(3) Japan experienced less influence than usual from the
Okhotsk High (a cool semi-stationary anticyclone).

These atmospheric features and possible factors contributing to them are illustrated in Figure 31. The abovementioned primary factors are supported by statisticalanalysis and research performed to date, but the results ofthis work do not completely explain the extreme conditions
seen. In order to further understand the event and clarify
the dynamic mechanism behind it, it is necessary to investigate other possible factors and perform numerical modelexperiments.
(Shotaro Tanaka, Climate Prediction Division)

Figure 31 Schematic chart of primary factors contributing to Japan’s extremely hot summer (June – August) of 2010
The numbers of (1), (2) and (3) on this chart correspond to those in Section 4 of the main text.

References
Angell, J. K., 1990: Variation in global tropospheric temperature after adjustment for the El Niño influence,
1958-1989, Geophy. Res. Lett., 17, 1093-1096.
Enomoto, T., 2004: Interannual variability of the Boninhigh associated with the propagation of Rossby waves
along the Asian jet, J. Meteor. Soc. Japan, 82, 10191034.
Krishnan, R. and M. Sugi, 2001: Baiu rainfall variability
and associated monsoon teleconnections, J. Meteor. Soc.
Japan, 79, 851-860.
Nakamura, H. and T. Fukamachi, 2004: Evolution and dynamics of summertime blocking over the Far East andthe associated surface Okhotsk high, Quart. J. Roy. Meteor. Soc., 130, 1213-1233.
Nitta, T., 1987: Convective activities in the tropical western
Pacific and their impact on the Northern Hemispheresummer circulation, J. Meteor. Soc. Japan, 65, 373-390.
Seager, R., N. Harnik, Y. Kushnir, W. Robinson, and J.
Miller, 2003: Mechanisms of hemispherically symmetricclimate variability, J. Climate, 16, 2960-2978.

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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