南海及周边地区晚春初夏降水变异关联主模态及其机理

Coherent leading modes of precipitation variation in late spring and early summer over the South China Sea and surrounding area and their mechanisms

基于近38年的观测资料,对南海及周边地区5、6份降水变异关联主模态及其机理进行了统计诊断分析。南海及周边地区5、6月份降水的第一关联主模态反映出5、6月的降水变异的空间分布相似,即中南半岛、南海及菲律宾海均为同号区,而在中国南方地区则与之反号;时间尺度上以年际变化为主。该模态与前期发生的ENSO事件有密切联系,在ENSO冷事件(暖事件)的强迫作用下,使得5、6月份在南海-菲律宾附近出现持续的异常气旋(反气旋),进而影响南海及周边地区的降水的持续异常。第二模态显示南海及周边地区5月、6月降水异常的空间分布大致反相,其中在南海中部及菲律宾海的降水异常与我国东部的降水负异常反号;时间尺度以年代际变化为主。该模态主要是受南海夏季风爆发时间出现年代际提前的影响所致,其中又以低频季内分量的年代际变异的作用更为重要。

The coherent leading modes of precipitation variation over the South China Sea and surrounding area in May and June and their mechanisms statistically were studied,based on the observed data in recent thirty-eight years.The first coherent leading mode shows the similar spatial patterns of precipitation anomalies in May and June.The anomalies in the Indochina Peninsula,the South China Sea and the Philippine Sea are in-phase,which are out of phase with the anomalies in southern China.The first principle component is dominant on interannual time scale.This first leading mode is closely attributed to ENSO events occurred in the previous year.The cold(warm)ENSO events force the persistent anomalous cyclone(anti-cyclone)over the South China Sea and the Philippine Sea in May to June,which eventually leads to a persistent anomalous precipitation over the South China Sea and surrounding areas.The second coherent mode exhibits a rough anti-phase spatial distribution in May and in June.The anomalies in the east part of China are anti-phase to those in the central South China Sea and the Philippine Sea.The second principle component is dominant on interdecadal time scale.This mode is mainly attributed to the advanced interdecadal change of the South China Sea summer monsoon onset affected strongly by the interdecadal change of evolution of low frequent intraseasonal oscillation.