The Interannual Variability Of East Asian Summer Monsoon And Its Relationship With Subsurface Ocean Temperature Over The Pacific

Based on the Japan Meteorological Agency historical ocean temperature analysis data, NCEP/NCAR reanalysis dataset, the monthly mean precipitation and temperature at 160 meteorological stations in China, the interannual variation of East Asian Summer Monsoon pattern, the relationship between previous Pacific subsurface ocean temperature (SOTA) and East Asian Summer Monsoon is analyzed, and the way how SOTA probably affects the East Asian Summer Monsoon circulation are discussed. The results shows that:(1) East Asian summer monsoon(EASM) has obvious interannual variation, when the EASM strengthens, the Northwest Pacific sea level pressure is low, weak subtropical, tropical northwest south of 30° N in the Pacific, including the Southern China coast as abnormal cyclonic circulation in northern China, the Korean Peninsula to Japan for anti-cyclonic circulation, is conducive to the summer monsoon northward, for the weak monsoon years, and vice versa. strong summer monsoon years easily lead to the Yangtze River basin precipitation, summer temperature is higher, while for weak summer monsoon year, the Yangtze River Basin Rainfall, lower temperature in summer.(2) The first mode of the Pacific subsurface ocean temperature (SOTA) is characterized by warm and cold phase of ENSO cycle. The second mode shows that the anomalies of SOTA in the warm pool propagate and expand eastwards with the seasonal evolution, which makes a precursory prediction signal for ENSO. There is a significant leading correlation between the previous SOTA and post-East Asian summer monsoon. The current period of autumn and winter in the Western Pacific Warm Pool subsurface ocean temperatures warm (cold) and a trend is clearly spread eastward, it will equatorial Pacific cold (warm) SST warming (cold), when the East Asian summer monsoon is stronger (weak).(3) Subsurface temperature have significant decadal variations, mainly for the late 1970’s the interdecadal abrupt change, different interdecadal background of East Asian summer atmospheric circulation changes obviously, abrupt climate change, between East Asia Summer Monsoon and the subsurface temperature has significant correlation. Once an El Nino type SOTA patterns with a warm anomaly in the eastern Pacific and a cold one in the western Pacific, the western Pacific subtropical high is enhanced. An anomalous anticyclone with its southwesterly winds prevailing on western North Pacific, that carries moisture to Yangtze River Basin and Huaihe Basin, which favors a positive precipitation anomaly and a weak EASM. but the impact of El Nino type SOTA pattern on the East Asian summer climate change more significant than La Nina patterns. The SOTA affects on EASM mainly through its persistence, which leads sustained effects to the general circulations over East Asian Pacific. When the continuous positive(negative) SOTA in the warm pool moves eastwards, the sea surface temperature (SST) of East Pacific becomes cold (warm); The cold (warm) SST in turn strengthens the sea SOTA, As a result, a meridional wave train in general circulation is constructed over East Asia in summer, atmospheric circulations in East Asia may form the meridional wave train structure in the summer, Through anomalous western North Pacific anticyclone(cyclone) circulation, which then changes the general circulation an climate in East Asian.