The Synergy Between The East Asian Summer Monsoon And The South Asian Summer Monsoon And Its Relations With Regional Rainfall In China

Using the precipitation data in China and the reanalysis data from European Centre for Medium-Range Weather Forecasts(ECMWF)during the period of 1979 to 2014,the index for the interface between the East Asian summer monsoon and the Indian summer monsoon(IIEI)defined by Cao is calculated,and the interannual variation of IIEI,the feature of its positive-anomaly and negative-anomaly years,as well as the relations between IIEI and China's regional precipitation are also analyzed on the basis of the comparison between IIEI and the indices of East Asian summer monsoon and the Indian summer monsoon by Empirical Orthogonal Function(EOF),correlation analysis,wavelet analysis,composite analysis and differential analysis.The results show that the IIEI has positive correlation with the index of East Asian summer monsoon and negative correlation with the Indian summer monsoon,and it has a stable fluctuation with a period of 3-5 years.Meanwhile,there are negative correlations between IIEI and precipitation in most of the southern China.In the positive-anomaly years of IIEI,the East Asian summer monsoon is stronger than Indian summer monsoon,the intensity of South Asian high is weaker and its position is both by south and by west,and the intensity of West Pacific subtropical high is weaker and the location is both by east and by north.The south China is controlled by the northeastern winds.And it is northerly wind at the low level of the South China Sea,which inhibits the transport of water vapor to the southern China.The sinking movement results in the less precipitation in the most southern China and cause drought easily.In negative-anomaly years of IIEI,the East Asian monsoon is weaker than the South Asian monsoon.The intensity of South Asian high is stronger and its position is east shifting,and the strength of the West Pacific subtropical high is stronger and its position is both by west and by south.The southern China is controlled by the southwest wind.And it is southerly wind at the low level of the South China Sea,and the water vapor from the Arabian Sea and the Bay of Bengal transports to the vast areas of the southern China by the south airflow,and meets with the dry-cool airflow from the north.Because of the anomalous upward movement,it brings much more precipitation in the southern China and is easy to cause floods.Therefore,thesynergistic evolution of the East Asian monsoon and the South Asian monsoon is the important reason for the anomalous precipitation in the southern China.And IIEI can reflect the synergistic variation of the East Asian monsoon and the South Asian monsoon and its joint influences on the weather-climate in China.