南海夏季风爆发与前期东亚冬季风异常的关系以及ENSO的作用

基于ERA-interim再分析资料采用相关分析研究了东亚冬季风和南海夏季风爆发的关系，并探讨了ENSO在其中的作用。结果表明，弱冬季风之后的南海地区5月有异常东风、降水偏少，对应于夏季风爆发偏晚；强冬季风之后则相反；但上述关系并不十分显著。进一步利用线性回归将东亚冬季风分为与ENSO有关和无关的部分，对于与ENSO有关的冬季风，上述冬季风-夏季风爆发的关系的显著性有明显提高；但与ENSO无关的冬季风和夏季风爆发并无显著联系。这说明冬季风-南海夏季风爆发的关系主要是由与ENSO有关的冬季风造成的。这一关系可以用ENSO激发的菲律宾异常反气旋或气旋来解释，以弱冬季风之后夏季风爆发偏晚为例:El Ni?o事件一方面激发出菲律宾异常反气旋，使得冬季风偏弱；另一方面又引起热带印度洋增暖，由于局地海气相互作用正反馈和印度洋电容器效应，菲律宾异常反气旋得以维持到晚春。该异常反气旋及其南侧的异常东风不利于南海夏季风的爆发，从而导致夏季风爆发偏晚。

The Relationship between the East Asian Winter Monsoon Anomaly and the Subsequent Summer Monsoon Onset over the South China Sea and the Impact of ENSO

Linkage between the East Asian winter monsoon (EAWM) and the South China Sea (SCS) summer monsoon onset (SCSSMO) and the impacts of ENSO have been studied by applying the method of correlation analysis to the ERA-interim reanalysis dataset. Anomalous easterly winds and less precipitation in the SCS tend to occur during May after a weak EAWM, which corresponds to the situation of late onset of the summer monsoon. However, this relationship is not robust during the time period of study. We further separate the EAWM into an ENSO-related part (EAWM_EN) and an unrelated part (EAWM_res) by linear regression method. The results indicate that the link of the EAWM_EN to the SCSSMO becomes statistically significant, but the link of the EAWM_res to the SCSSMO is very weak. Hence, the EAWM-SCSSMO relationship is mainly caused by the anomalous winter monsoon associated with ENSO. And this relationship can be explained by the anomalous anticyclone/cyclone over the Philippine Sea (AACPS/ACPS) associated with ENSO. For example, during an El Niño event, anomalous anticyclone over the east of Philippine is induced and the tropical Indian Ocean tends to be warmer. Due to the positive feedback of the local air-sea interaction and the Indian Ocean capacitor effect, this AACPS can be maintained and persist until late spring. The anomalous easterly winds on the south of AACPS may be unfavorable for the onset of summer monsoon. Therefore, the SCSSMO tends to be late in the El Niño year.