华南降水季节演变的年代际变化

INTERDECADAL CHANGE OF THE SEASONAL EVOLUTION OF RAINFALL OVER SOUTH CHINA

利用中国测站的逐日降水资料和NCEP/NCAR再分析资料,分析了近35年华南降水季节演变的年代际变化特征及其相关的大气环流异常特征。华南地区降水季节分布型在1990年代初期发生了年代际转变,其中,华南西部降水在1990年之前为双峰型分布,1990年之后变为以6月为峰值的单峰型分布;华南东部降水在1990年之前是以5月、8月为峰值的弱双峰型分布,1990年之后变为以6月、8月为峰值的显著双峰型分布。华南东、西部降水季节分布的年代际变化分别与华南全区6月降水量的年代际增加以及8月华南东、西部降水显著反相的年代际变化(东多西少)密切相关。1990年之后,大雨及以上强降水事件发生频率的增强是导致上述年代际变化的主要原因。华南6月降水年代际的增强与南海区域的西北太平洋副热带高压(简称西太副高)脊线位置的年代际异常偏南密切相关。7月华南地区降水的年代际增加与西太副高年代际东撤及影响华南地区的热带气旋频数年代际增多有关。8月华南东、西部降水显著反相的年代际变化(东多西少),一方面受印度洋及南海上空夏季风年代际减弱的影响,使得输送到华南西部的水汽减少,另一方面西太副高的年代际增强并西伸,使得源自副高西南侧的水汽更直接输送至华南东部地区有关;同时也与登陆和影响华南东、西部的热带气旋的年代际增多和减少有关。

This paper studies the interdecadal change of the seasonal evolution of rainfall over South China and its atmospheric circulation anomalies in the recent 35 years,based on the observed daily precipitation data from 1979 to 2013 provided by China Meteorological Administration and the reanalysis data of NCEP/NCAR.The seasonality of rainfall evolution in South China experienced an interdecadal change in the early 1990s.However,the interdecadal changes of rainfall seasonality in the eastern and western South China are different to each other.The precipitation pattern of seasonal distribution in the western South China changed from a bimodal pattern to an unimodal pattern with a peak in June around 1990,while in the eastern South China the weak bimodal precipitation pattern with two peaks in May and August,respectively,turned into a significant bimodal pattern with two peaks appearing in June and August,respectively,around 1990.The study also shows that the interdecadal changes of the seasonal precipitation pattern in both eastern and western South China are closely related to the interdecadal increase of precipitation in June in South China and the significant inverse interdecadal change in the east and the west of South China(less rainfall in the west part and more rainfall in the east part)in August,which are directly contributed by the significant interdecadal change of heavy precipitation frequency around 1990.The increase of precipitation over South China in June is caused by the interdecadal southward advancement of the western Pacific subtropical high after 1990,while the interdecadal increase of precipitation over South China in July results from the interdecadal eastward withdrawal of the western Pacific subtropical high,and the interdecadal increase of tropical cyclones affecting South China.The significant out-of-phase interdecadal change in both the east and west part of South China in August is associated with the interdecadal weakening of South tropical Asian summer monsoon,which leads to a weak transport of water vapor to the western South China,and the interdecadal intensification of the western Pacific Subtropical high and its westward extension forced by the interdecadal warming of sea surface temperature in the subtropical northwestern Pacific,which results in intensified water vapor transport to the eastern South China from the southwestern flank of the western Pacific subtropical high.Meanwhile,the interdecadal change of tropical cyclones affecting South China has direct impact on the interdecadal change of precipitation over South China in August.