东亚季风环流由夏向冬的季节转变与中国前冬气候的关系

Relationship Between the Seasonal Transition of East Asian Monsoon Circulation from Summer to Winter and Early Winter Climate in China

利用NCEP/NCAR再分析资料、CMAP降水及Hadley环流中心海温资料等,对东亚季风环流由夏向冬的季节转变与中国前冬气候的关系进行了研究。参考前人定义的亚太热力差指数,计算了1979-2016年亚太热力场由夏向冬的季节转变时间(平均为56. 6候)。结果表明,该季节转变时间点能很好地表征东亚季风环流由夏向冬的季节转变。东亚季风环流由夏向冬的转变特征表现为:低层大陆热低压转为大陆冷高压,阿留申低压形成加强,低空偏南风转为偏北风;中层东亚大槽形成,副高单体减弱成一个副热带高压带;高层南亚高压中心从青藏高原移至菲律宾以东洋面上,高空偏北风转为偏南风。此外由夏向冬的季节转变时间与中国前冬降水和地面气温有着紧密的联系,并且该转变时间的早晚与前期夏季热带太平洋的海温呈现类ENSO异常海温型的相关分布,即表现为前期夏季热带中东太平洋海温偏低(高)时,后期东亚夏季型季风环流向冬季型季风环流转变易偏晚(早),这对东亚季风环流季节转变的预测提供了依据。

The NCEP/NCAR reanalysis,CMAP rainfall and Hadley centre SST datasets are used to investigate the relationship between the seasonal transition of East Asian monsoon circulation from summer to winter and early winter climate in China.It is found that,based on the Asia Pacific thermal difference index （APTDI）in 19792016 defined before,the time of seasonal transition from summer to winter determined by the APTDI （average in pentad 56.6） can well represent the characteristic and process of the seasonal change in East Asian monsoon circulation from summer to winter.The transition characteristic of the circulation can be summarized as follows.The continental warm low at lower tropospheric level turns to the continental cold high and the Aleutian low has formed,while the low level southerly winds turn to be northerly winds.At mid tropospheric level,the East Asia major trough forms gradually and the subtropical high changes to a high pressure belt.Furthermore,the South Asia high shifts from the Tibetan Plateau to the east of Philippines,together with prevailing northerly into southerly at upper tropospheric level.It is concluded that the transition time of East Asian monsoon circulation from summer to winter is close related to early winter rainfall and land surface temperature of China.And there is a significant ENSO like correlation pattern between the seasonal transition time and previous summer SST anomalies,which means it can provide a basis for the prediction of the seasonal transition of East Asian monsoon circulation.