Download leading mode of indian ocean sst and its impacts on asian summer

LEADING MODE OF INDIAN OCEAN SST AND ITS
IMPACTS ON ASIAN SUMMER MONSOON
1,2
1
1
2
Yang Mingzhu Ding Yihui Li Weijing Mao Hengqing
1 Laboratory for Climate Studies, China Meteorological Administration, National
Climate Center, Beijing 100081
2 Group of Meteorological Audio & Video Information, China Meteorological Ad
ministration, Beijing 100081
Abstract
The Indian Ocean sea surface temperature (SST) was analyzed by using empirical o
rthogonal function (EOF), and the leading mode of Indian Ocean SST (LMIO) was
extracted. The Major spatial and temporal characters of LIMO were discussed. Based
on the above analysis, the relationships between LMIOS and China summer rainfalls
(CSR) were further investigated, and the impacts of LMIOS on Asian summer monsoon
circulation were explored. The following notable results are obtained: the
significant evolutional characters of LMIO are the consistent warming trend of
almost the whole Indian Ocean basin, the distinctive quasi 3 and quasi 10
oscillations and remarkably interdecadal warming in 1976/1977 and 1997/1998,
respectively. The increasing trend of LMIO was close related with CSR, i.e. it was
close related with reductions in the summer precipitation in North China, southern
Northeast China, eastern South China and western Southwest China, and with increases
in summer precipitation in the middle and lower reaches of Yangtze River, northern
Northeast China and Northwest China. And it was rather close/positively related with
Meiyu precipitation in the middle and lower reaches of Yangtze River. The LMIO rising
trend had distinctive impacts on the Asian summer monsoon system and the water vapor
transports. That is to say, the consistent rising trend of LMIO was associated with
the weakening of South Asian high, the easterly south of the Tibetan plateau, and
the cross equatorial flows over the South China sea-Southeast Asia -southwest Indian
ocean area, and the strengthening of northerly winds over 10°N-20°N, 40°E-110°
E at the upper level; with the strengthening of northwest Pacific ocean subtropical
high and its larger area at the middle level; and with the strengthening of Somali
cross equatorial jet and the weakening of the low circulation of Indian summer
monsoon in the sector of India and Indian ocean, and the strengthening of lower level
south wind over the middle and lower reaches of Yangtze River and South China and
the weakening of lower level southwesterly over North China; and with the increase
in ground surface pressure over the Asian continent. Changes in the moisture flux
transport integrated vertically over the whole troposphere are similar with those
in the lower level circulation. To sum up, the significant SST increasing trend of
Indian Ocean basin was one of the important causes for the weakening of the Asian
summer monsoon circulation and the southward shift of summer rain band in China.
Key words: Leading EOF mode of Indian Ocean SST, Indian summer monsoon rainfall,
China summer rainfall, Asian summer monsoon, Water vapor transport.