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《科学通报(英文版)》 2013-06
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Precursory influence of the Antarctic Oscillation on the onset of Asian summer monsoon

GAO Hui *,LIU YunYun,WANG YongGuang & LI WeiJing National Climate Center,China Meteorological Administration,Beijing 100081,China  
The Asian summer monsoon(ASM) begins firstly over the Indo-China Peninsula in early May and over the South China Sea(SCS) in mid-May.The different monsoon onset dates can exert distinct effects on the summer rainfall in Asia.Statistical results indicate that the Antarctic Oscillation(AAO) in the boreal winter has a significant precursory influence on the ASM onset dates.In stronger AAO years,both the Mascarene high and the Australia high in March are stronger owing to the "see-saw" structure of atmospheric circulation over the subtropics and higher latitudes in the Southern Hemisphere,and the tropical intertropical convergence zone(ITCZ) is deeper.Thus,the pressure gradient between the subtropical and tropical regions increases in spring.As a result,the Somalia cross-equatorial flow(SCEF) occurs earlier,strengthens,and enhances the westerlies over the tropical Indian Ocean.The enhanced westerlies impel an eastward withdrawal of the western Pacific subtropical high and intensify the convergence and rising motion at the lower troposphere,accelerating the burst of ASM.Differently,weaker AAO weakens the pressure gradient between the tropical and subtropical regions and delays the establishment of SCEF,resulting in a delayed onset of ASM.This study extends the leading time of seasonal forecast of ASM onset from the previous spring to winter and provides useful information about precursory signals in climate prediction operation.
【Fund】: supported by the National Basic Research Program of China (2012CB417205);; the International Cooperation Program of Ministry of Science and Technology of China (2009DFA23010);; the Special Research Fund of Public Welfare Project (Meteorology:GYHY200906018 and GYHY201306070);; the National Science & Technology Supporting Program (2009BAC51B)
【CateGory Index】: P425.42
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