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HOME > Climate System Monitoring > Composite map for El Niño / La Niña events > Composite analysis of atmospheric circulation in El Niño and La Niña events

Composite analysis of atmospheric circulation in El Niño and La Niña events

JMA has updated its statistical analysis on the relationship between El Niño Southern Oscillation (ENSO) and atmospheric circulation using the Japanese 25-year reanalysis (JRA-25; Onogi et al. 2007) and the JMA Climate Data Assimilation System (JCDAS) dataset. As a result, new statistical products based on the Japanese 55-year reanalysis dataset (JRA-55; Kobayashi et al. 2015) are available. This page outlines statistical analysis of atmospheric circulation and related characteristics.


Data and methods

Sea surface temperatures (SSTs) are based on COBE-SST datasets (JMA 2006; http://ds.data.jma.go.jp/tcc/tcc/products/elnino/cobesst_doc.html). Atmospheric circulation data are based on JRA-55 (http://jra.kishou.go.jp/JRA-55/index_en.html), and tropical convective activity is inferred from outgoing longwave radiation (OLR). The original OLR data are from observations conducted by NOAA's polar-orbiting satellites. High-frequency variations such as eddy kinetic energy are defined as two- to eight-day band-pass filtered fields. Monthly and three-month mean fields are calculated from these datasets.

The base period for the analysis is 1958 - 2012 (1979 - 2012) for SST and JRA-55 (OLR) datasets, while that for the three-month periods from November to January and December to February is 1958/59 - 2012/13 (1979/80 - 2012/13). Anomalies are defined as deviations from the average in these periods. It has been suggested that atmospheric response to tropical SST anomalies during El Niño events does not always correspond to that observed during La Niña events (Hoerling et al. 2001). Composite analysis of anomaly fields has been performed in consideration of the asymmetric relationship between these events.

The El Niño Monitoring Indices used in analysis and for the corresponding regions are shown in Table.1. In the definition of El Niño and La Niña phases, the five-month running mean SST deviation in NINO.3, NINO.WEST and IOBW satisfies the threshold requirements shown in Table.1 for at least six consecutive months. The definition for NINO.3 is based on that used by JMA. The SST deviation is defined as the deviation from the latest sliding 30-year period.


Table 1 El Niño Monitoring Indices
ENSO Index Area ENSO threshold (five-month running mean)
La Niña phase El Niño phase
NINO.3 Eastern Pacific 5ºS - 5ºN, 150ºW - 90ºW Below -0.5ºC Above +0.5ºC
NINO.WEST Western Pacific EQ - 15ºN, 130ºE - 150ºE Above +0.15ºC Below -0.15ºC
IOBW Indian Ocean Basin 20ºS - 20ºN, 40ºE - 100ºE Below -0.15ºC Above +0.15ºC

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Statistical characteristics

This section outlines the characteristics of seasonal mean composite anomalies in the positive and negative phases of the ENSO indices.

1. Atmospheric circulation in the El Niño (positive) phase of NINO.3

Winter (December - February)

OLR and precipitation anomalies indicate that convective activity is enhanced over the central to eastern equatorial Pacific and suppressed over and around the Maritime Continent in response to the east-west contrast of SST anomalies over the equatorial Pacific. Enhanced convective activity is seen over the Gulf of Mexico, and suppressed convective activity is seen over the South Pacific Convergence Zone (SPCZ), the northern part of South America and the tropical North Atlantic. The Inter-Tropical Convergence Zone (ITCZ) exhibits equatorward shift.

In the lower troposphere, cyclonic (anti-cyclonic) circulation anomalies straddling the equator are seen, and westerly (easterly) wind anomalies are dominant over western to central parts of the Pacific (the eastern Indian Ocean to the Maritime Continent and the Atlantic). These patterns are consistent with those of the gMatsuno - Gillh response (Matsuno 1966, Gill 1980) to convective heat source anomalies. In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere. Zonal wind anomalies in the lower and upper troposphere indicate weaker-than-normal Walker Circulation.

The subtropical jet stream demonstrates a southward shift over the area from the Middle East to East Asia in line with cyclonic circulation anomalies in the upper troposphere. The jet stream exhibits northward meandering to the east of Japan. In the 500-hPa height field, wave trains such as the Pacific - North American (PNA) pattern (Wallace and Gutzler 1981) are seen over the area from the tropical North Pacific to North America with negative anomalies to the south of Alaska. In line with these anomalies, negative sea-level pressure anomalies are seen to the south of Alaska, indicating enhancement and eastward shifting of activity associated with the Aleutian Low.

Spring (March - May)

OLR and precipitation anomalies indicate that convective activity is enhanced over the central to eastern equatorial Pacific and suppressed over and around the Maritime Continent in response to the east-west contrast of SST anomalies over the equatorial Pacific. Suppressed convective activity is seen over the equatorial Atlantic and the north Indian Ocean.

In the lower troposphere, cyclonic (anti-cyclonic) circulation anomalies straddling the equator are seen, and westerly (easterly) wind anomalies are dominant over the equatorial Pacific (from the Indian Ocean to the Maritime Continent and the equatorial Atlantic). In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere, indicating weaker-than-normal Walker Circulation.

The subtropical jet stream exhibits a southward shift over the area from the Middle East to southern China. In the 500-hPa height field, positive anomalies are seen over Japan in line with the northward meandering of the jet stream.

Summer (June - August)

OLR and precipitation anomalies indicate that convective activity is enhanced over the equatorial Pacific and suppressed over the Maritime Continent in response to the east-west contrast of SST anomalies over the equatorial Pacific. Suppressed convective activity is seen over India, indicating an inactive Indian monsoon. The coefficient of correlation between the NINO.3 index and the intensity of the Asian summer monsoon (SAMOI-A) is a statistically significant negative value, indicating the weaker-than-normal Asian monsoon circulation seen in El Niño events (not shown).

In the lower troposphere, cyclonic circulation anomalies straddling the equator are seen, and westerly wind anomalies are dominant over the Pacific. In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere. Cyclonic circulation anomalies are seen over vast areas of southern Eurasia, indicating a weaker-than-normal Tibetan High in its northern part and a southward shift of the subtropical jet stream.

In the 500-hPa height field, negative anomalies are seen over Japan and the North Pacific in line with southward meandering and enhancement of the jet stream over Japan and the North Pacific, respectively. In the sea level pressure and 850-hPa stream function fields, negative anomalies are seen over vast areas of the North Pacific, indicating a weaker-than-normal subtropical high.

Autumn (September - November)

OLR and precipitation anomalies indicate that convective activity is enhanced over the equatorial Pacific and suppressed over and around the Maritime Continent in response to the east-west contrast of SST anomalies over the equatorial Pacific.

In the lower troposphere, cyclonic (anti-cyclonic) circulation anomalies straddling the equator are seen, and westerly (easterly) wind anomalies are dominant over the western to central Pacific (the Indian Ocean). In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere, indicating weaker-than-normal Walker Circulation.

The subtropical jet stream exhibits a southward shift over vast areas from Northern Africa to the North Pacific in line with cyclonic circulation anomalies in the upper troposphere.

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2. Atmospheric circulation in the La Niña (negative) phase of NINO.3

Winter (December - February)

OLR and precipitation anomalies indicate that convective activity is suppressed over the western to central equatorial Pacific and enhanced over and around the Maritime Continent in response to the east-west contrast of SST anomalies in the equatorial Pacific. Enhanced convective activity is seen over the South Pacific Convergence Zone (SPCZ) and the northern part of South America, and suppressed convective activity is seen over and around the Gulf of Mexico.

In the lower troposphere, anti-cyclonic (cyclonic) circulation anomalies straddling the equator are seen, and easterly (westerly) wind anomalies are dominant over the western to central Pacific (from the eastern Indian Ocean to the Maritime Continent). In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere. Zonal wind anomalies in the lower and upper troposphere indicate stronger-than-normal Walker Circulation.

The subtropical jet stream exhibits a northward shift over East Asia in line with anti-cyclonic circulation anomalies in the upper troposphere. The jet stream is stronger than normal over Japan. In the 500-hPa height field, wave trains such as the PNA pattern are seen over the area from the tropical North Pacific to North America with positive anomalies to the south of Alaska. In line with the positive anomalies, positive sea-level pressure anomalies are seen to the south of Alaska, indicating a weakening and westward shift of the Aleutian Low activity.

Spring (March - May)

OLR and precipitation anomalies indicate that convective activity is suppressed over the equatorial Pacific and enhanced over and around the Maritime Continent in response to the east-west contrast of SST anomalies. Enhanced convective activity is seen over the equatorial Atlantic and the north Indian Ocean.

In the lower troposphere, anti-cyclonic (cyclonic) circulation anomalies straddling the equator are seen, and easterly (westerly) wind anomalies are dominant over the equatorial Pacific (from the Indian Ocean to the Maritime Continent). In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere, indicating stronger-than-normal Walker Circulation. The subtropical jet stream exhibits a northward shift over South to East Asia.

Summer (June - August)

OLR and precipitation anomalies indicate that convective activity is suppressed over the equatorial Pacific and enhanced over the Maritime Continent in response to the east-west contrast of SST anomalies. Enhanced convective activity is seen over India, indicating an active Indian monsoon. The statistical relationship between NINO.3 and SAMOI-A indicates the stronger-than-normal Asian monsoon circulation seen in La Niña events (not shown).

In the lower troposphere, anti-cyclonic circulation anomalies straddling the equator are seen, and easterly wind anomalies are dominant over the Pacific. In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere. Anti-cyclonic circulation anomalies are seen over Eurasia, especially over Central Asia and the northeastern part of East Asia, indicating a stronger-than-normal Tibetan High in its northern part and a northward shift of the subtropical jet stream.

In the 500-hPa height field, positive anomalies are seen over Japan in line with northward meandering of the jet stream. In the sea level pressure and 850-hPa stream function fields, positive anomalies are seen over vast areas of the North Pacific, indicating a stronger-than-normal subtropical high.

Autumn (September - November)

OLR and precipitation anomalies indicate that convective activity is suppressed over the equatorial Pacific and enhanced over and around the Maritime Continent in response to the east-west contrast of SST anomalies over the equatorial Pacific.

In the lower troposphere, anti-cyclonic (cyclonic) circulation anomalies straddling the equator are seen, and easterly (westerly) wind anomalies are dominant over the western to central Pacific (the Indian Ocean). In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere, indicating stronger-than-normal Walker Circulation.

The subtropical jet stream exhibits a northward shift over vast areas of southern Eurasia in line with anti-cyclonic circulation anomalies in the upper troposphere.

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3. Atmospheric circulation in the El Niño (negative) phase of NINO.WEST

Winter (December - February)

OLR and precipitation anomalies indicate that convective activity is enhanced over the central to eastern equatorial Pacific in line with equatorward shift of the ITCZ and suppressed over and around the Maritime Continent in response to the east-west contrast of SST anomalies over the equatorial Pacific. Enhanced convective activity is seen over the Gulf of Mexico, and suppressed convective activity is seen over the South Pacific Convergence Zone (SPCZ), the northern part of South America and the tropical North Atlantic.

In the lower troposphere, cyclonic (anti-cyclonic) circulation anomalies straddling the equator are seen and westerly (easterly) wind anomalies are dominant over the western to central Pacific (the Maritime Continent). In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere. Zonal wind anomalies in the lower and upper troposphere indicate weaker-than-normal Walker Circulation.

The subtropical jet stream exhibits a southward shift over the area from Northern Africa to East Asia in line with cyclonic circulation anomalies in the upper troposphere. The jet stream exhibits northward meandering to the east of Japan. In the 500-hPa height field, positive anomalies are seen to the east of Japan.

Spring (March - May)

OLR and precipitation anomalies indicate that convective activity is enhanced over the central to eastern equatorial Pacific and suppressed over and around the Maritime Continent in response to the east-west contrast of SST anomalies over the equatorial Pacific. Suppressed convective activity is seen over the equatorial Atlantic and the north Indian Ocean.

In the lower troposphere, cyclonic circulation anomalies straddling the equator are seen and westerly wind anomalies are dominant over the equatorial Pacific. In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere.

The subtropical jet stream exhibits a southward shift over the area from the Middle East to southern China. In the 500-hPa height field, positive anomalies are seen over Japan.

Summer (June - August)

OLR and precipitation anomalies indicate that convective activity is enhanced over the equatorial Pacific and suppressed over the Maritime Continent in response to the east-west contrast of SST anomalies over the equatorial Pacific.

In the lower troposphere, cyclonic circulation anomalies straddling the equator are seen, and westerly wind anomalies are dominant over the western to central Pacific. In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere.

The subtropical jet stream exhibits a southward shift over the area from East Asia to the North Pacific. In the 500-hPa height field, negative anomalies are seen over the area from Japan to the North Pacific in line with southward meandering or enhancement of the jet stream over the area. In the sea level pressure and 850-hPa stream function fields, negative anomalies are seen over vast areas of the North Pacific, indicating a weaker-than-normal subtropical high.

Autumn (September - November)

OLR and precipitation anomalies indicate that convective activity is enhanced over the equatorial Pacific and suppressed over and around the Maritime Continent in response to the east-west contrast of SST anomalies over the equatorial Pacific.

In the lower troposphere, cyclonic circulation anomalies straddling the equator are seen and westerly wind anomalies are dominant over the western to central Pacific. In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere.

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4. Atmospheric circulation in the La Niña (positive) phase of NINO.WEST

Winter (December - February)

OLR and precipitation anomalies indicate that convective activity is suppressed over the western to central equatorial Pacific and enhanced over and around the Maritime Continent in response to the east-west contrast of SST anomalies over the equatorial Pacific. Enhanced convective activity is seen over the South Pacific Convergence Zone (SPCZ) and the northern part of South America, and suppressed convective activity is seen over the Gulf of Mexico.

In the lower troposphere, anti-cyclonic (cyclonic) circulation anomalies straddling the equator are seen and easterly (westerly) wind anomalies are dominant over the western to central Pacific (over the area from the eastern Indian Ocean to the Maritime Continent). In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere. Zonal wind anomalies in the lower and upper troposphere indicate stronger-than-normal Walker Circulation.

The subtropical jet stream exhibits a northward shift over East Asia in line with anti-cyclonic circulation anomalies in the upper troposphere. The jet stream is stronger than normal over Japan. The 500-hPa height field shows negative anomalies over and around Japan, and sea level pressure shows negative anomalies to the east of Japan.

Spring (March - May)

OLR and precipitation anomalies indicate that convective activity is suppressed over the equatorial Pacific and enhanced over and around the Maritime Continent in response to the east-west contrast of SST anomalies over the equatorial Pacific.

In the lower troposphere, anti-cyclonic circulation anomalies straddling the equator are seen and easterly wind anomalies are dominant over the western to central equatorial Pacific. In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere.

The subtropical jet stream exhibits a southward shift over the area from Japan to the western North Pacific. In the 500-hPa height field, negative anomalies are seen over Japan.

Summer (June - August)

OLR and precipitation anomalies indicate that convective activity is suppressed over the equatorial Pacific and enhanced over the Maritime Continent in response to the east-west contrast of SST anomalies over the equatorial Pacific.

In the lower troposphere, anti-cyclonic circulation anomalies straddling the equator are seen and easterly wind anomalies are dominant over the western to central Pacific. In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere.

Autumn (September - November)

OLR and precipitation anomalies indicate that convective activity is suppressed over the equatorial Pacific and enhanced over and around the Maritime Continent in response to the east-west contrast of SST anomalies over the equatorial Pacific.

In the lower troposphere, anti-cyclonic (cyclonic) circulation anomalies straddling the equator are seen and easterly (westerly) wind anomalies are dominant over the western to central Pacific (the Indian Ocean). In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere, indicating stronger-than-normal Walker Circulation.

The subtropical jet stream exhibits a northward shift over southern Eurasia in line with anti-cyclonic circulation anomalies in the upper troposphere.

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5. Atmospheric circulation in the El Niño (positive) phase of IOBW

Winter (December - February)

OLR and precipitation anomalies indicate that convective activity is enhanced over the central to eastern equatorial Pacific in line with equatorward shift of the ITCZ, and suppressed over and around the Maritime Continent in response to the east-west contrast of SST anomalies over the equatorial Pacific. Suppressed convective activity is seen over the South Pacific Convergence Zone (SPCZ).

In the lower troposphere, cyclonic (anti-cyclonic) circulation anomalies straddling the equator are seen, and westerly (easterly) wind anomalies are dominant over the western to central Pacific (over the area from the Indian Ocean to the Maritime Continent). In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere. Zonal wind anomalies in the lower and upper troposphere indicate weaker-than-normal Walker Circulation.

The subtropical jet stream exhibits a southward shift over the area from the Middle East to East Asia in line with cyclonic circulation anomalies in the upper troposphere. The jet stream exhibits northward meandering to the east of Japan. In the 500-hPa height field, positive anomalies are seen to the east of Japan.

Spring (March - May)

OLR and precipitation anomalies indicate that convective activity is suppressed over and around the Philippines.

In the lower troposphere, cyclonic circulation anomalies are seen over the central equatorial North Pacific, anti-cyclonic circulation anomalies straddling the equator are seen, and easterly wind anomalies are dominant over and around the Maritime Continent. In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere.

In the 500-hPa height field, positive anomalies are seen over Japan in line with the northward shift of the jet stream.

Summer (June - August)

OLR and precipitation anomalies indicate that convective activity is suppressed over the Philippines in response to the east-west contrast of SST anomalies over the equatorial Pacific.

In the lower troposphere, northeasterly or easterly wind anomalies are seen in and around the southern part of the South China Sea, and anti-cyclonic circulation anomalies are seen over the Philippines. These characteristics are consistent with those of Indian Ocean capacitor effect proposed by Xie et al. (2009).

In the 500-hPa height field, positive anomalies seen over Eastern Siberia indicate the frequent occurrence of blocking highs over the area. In association with these blocking highs, the Okhotsk high is seen over and around the Okhotsk Sea.

Autumn (September - November)

OLR and precipitation anomalies indicate that convective activity is enhanced over the central to eastern equatorial Pacific and suppressed over and around the Maritime Continent in response to the east-west contrast of SST anomalies over the equatorial Pacific. Suppressed convective activity is seen over the northern part of South America.

In the lower troposphere, cyclonic (anti-cyclonic) circulation anomalies straddling the equator are seen, and westerly (easterly) wind anomalies are dominant over the western to central Pacific (over the area from the Indian Ocean to the Maritime Continent). In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere. Zonal wind anomalies in the lower and upper troposphere indicate weaker-than-normal Walker Circulation. The jet stream exhibits a southward shift over vast areas from the Middle East to the North Pacific.

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6. Atmospheric circulation in the La Niña (negative) phase of IOBW

Winter (December - February)

OLR and precipitation anomalies indicate that convective activity is suppressed over the equatorial Pacific and enhanced over and around the Maritime Continent in response to the east-west contrast of SST anomalies over the equatorial Pacific. Enhanced convective activity is seen over the South Pacific Convergence Zone (SPCZ) and the northern part of South America.

In the lower troposphere, anti-cyclonic (cyclonic) circulation anomalies straddling the equator are seen, and easterly (westerly) wind anomalies are dominant over the western to central Pacific (over the area from the Indian Ocean to the Maritime Continent). In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere. Zonal wind anomalies in the lower and upper troposphere indicate stronger-than-normal Walker Circulation.

The subtropical jet stream exhibits a northward shift over the area over East Asia in line with anti-cyclonic circulation anomalies in the upper troposphere. In the 500-hPa height field, negative anomalies are seen over Japan.

Spring (March - May)

OLR and precipitation anomalies indicate that convective activity is suppressed over the western Pacific and enhanced over and around the Philippines.

In the lower troposphere, anti-cyclonic (cyclonic) circulation anomalies straddling the equator are seen, and easterly (westerly) wind anomalies are dominant over the western to central Pacific (over the area from the eastern Indian Ocean to the Maritime Continent). In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere. Zonal wind anomalies in the lower and upper troposphere indicate stronger-than-normal Walker Circulation.

The subtropical jet stream exhibits a northward shift over the area from South to East Asia. In the 500-hPa height field, negative anomalies are seen over Japan in line with southward shift of the jet stream.

Summer (June - August)

OLR and precipitation anomalies indicate that convective activity is suppressed over the central to eastern equatorial Pacific and enhanced to the east of the Philippines.

In the lower troposphere, anti-cyclonic (cyclonic) circulation anomalies straddling the equator are seen, and easterly (westerly) wind anomalies are dominant over the western Pacific (over the Maritime Continent). A tri-pole pattern with cyclonic circulation anomalies over the area from the Indochina Peninsula to the south of Japan and Eastern Siberia and anti-cyclonic circulation anomalies over eastern Japan is seen.

In the upper troposphere, the jet stream exhibits a northward shift over vast areas of Eurasia and northward (southward) meandering over Central Asia and Japan (over China). In the 500-hPa height field, positive anomalies are seen over northern Japan.

Autumn (September - November)

OLR and precipitation anomalies indicate that convective activity is suppressed over the central to eastern equatorial Pacific and the equatorial Indian Ocean, and enhanced over and around the Maritime Continent.

In the lower troposphere, anti-cyclonic (cyclonic) circulation anomalies straddling the equator are seen, and westerly (easterly) wind anomalies are dominant over the western to central Pacific (over the area from the eastern Indian Ocean to the Maritime Continent). In the upper troposphere, the signs of anomaly patterns are opposite to those observed in the lower troposphere. Zonal wind anomalies in the lower and upper troposphere indicate stronger-than-normal Walker Circulation.

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References

Gill, A. E., 1980: Some simple solutions for heat-induced tropical circulation. Q. J. Roy. Met. Soc. 106, 447-462.

Hoerling, M. P. and A. Kumar, T. Xu, 2001: Robustness of the nonlinear climate response to ENSO's extreme phases. J. Climate, 14, 1277-1293.

JMA, 2006: Characteristics of Global Sea Surface Temperature Data (COBE-SST), Monthly Report on Climate System, Separated Volume No. 12.

Kobayashi, S., Y. Ota, Y. Harada, A. Ebita, M. Moriya, H. Onoda, K. Onogi, H. Kamahori, C. Kobayashi, H. Endo, K. Miyaoka, and K. Takahashi, 2015: The JRA-55 Reanalysis: General Specifications and Basic Characteristics. J. Meteorol. Soc. Japan, 93, 5 - 48.

Matsuno, T., 1966: Quasi-geostrophic motions in the equatorial area. J. Meteor. Soc. Japan, 44, 25-43.

Onogi, K., J. Tsutsui, H. Koide, M. Sakamoto, S. Kobayashi, H. Hatsushika, T. Matsumoto, N. Yamazaki, H. Kamahori, K. Takahashi, S. Kadokura, K. Wada, K. Kato, R. Oyama, T. Ose, N. Mannoji and R. Taira, 2007: The JRA-25 Reanalysis. J. Meteor. Soc. Japan, 85, 369-432, doi:10.2151/jmsj.85.369.

Wallace, J.M., and D.S. Gutzler, 1981: Teleconnections in the geopotential height field during the Northern Hemisphere winter. Mon. Wea. Rev., 109, 784-812.

Xie, S-P, Hu K, J. Hafner, H. Tokinaga, Y. Du, G. Huang, T. Sampe, 2009: Indian ocean capacitor effect on Indo-western Pacific climate during the summer following El Niño, J. Climate, 22, 730 - 748.

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