华南春季降水的年代际变化及其与大气环流和海温的关系

利用1960—2010年中国降水资料、NCEP/NCAR再分析资料、NOAA提供的海表温度资料以及太平洋年代际振荡(Pacific Decadal Oscillation,PDO)指数,分析了华南春季降水的年代际变化特征及其与大气环流和海温的关系。结果表明:华南春季降水经历了偏少(1960—1971年)—偏多(1972—1992年)—次偏少(1993—2010年)三个阶段。第一阶段少雨期,500 hPa上西风气流较平直,不利于北方冷空气南下,华南地区的暖气团也不活跃,对应的水汽通量散度为异常辐散。第二阶段多雨期,500 hPa高度上,高原北部脊偏强,利于冷空气南下,与华南地区活跃的暖湿气团汇合,对应的水汽场上为水汽异常辐合。第三阶段少雨期,500 hPa西风气流上的槽脊系统偏强,利于北方强冷空气南下,孟加拉湾地区的南支槽填塞,南方暖湿空气向华南的输送减弱。华南春季降水与PDO指数存在正相关关系,从不同季节来看,在年代际时间尺度上,前期秋季的PDO指数与华南春季降水的正相关显著,PDO处于负位相时,华南春季降水偏少,反之亦然;从华南春季降水年代际变化的不同阶段来看,PDO指数与华南春季降水的正相关在1960—1971年少雨期较显著。

Interdecadal variation of spring precipitation in South China and its relationships with atmospheric circulation and SST

South China is one of the most frequent drought and flood areas in China.The main characteristics of precipitation in South China are long rainy season and large rainfall.Studying the distribution characteristics and variation rules of spring precipitation in South China can be used as a basis for the allocation and utilization of precipitation resources in spring and the early warning of drought and flood in South China.Most studies have mainly focused on the characteristics of spring precipitation and its influencing factors in South China at present,while there are few studies about the interdecadal variation of spring precipitation in South China.Interdecadal climate change is the background of monthly,seasonal and interannual climate changes and forecasts,and also affects climate change over a longer period of time.It is one of the key issues of climate change.So this paper intends to study the interdecadal variation of spring precipitation in South China,and the corresponding characteristics of atmospheric circulation and sea surface temperature(SST) anomaly.To investigate the subject of spring precipitation of 48 stations in South China,its interdecadal variation characteristics and its relationships with atmospheric circulation and SST,the daily precipitation data in China,NCEP/NCAR reanalysis data,and Pacific Decadal Oscillation(PDO) index and SST data provided from NOAA during 1960-2010 are used.This paper uses the common meteorological statistical methods and diagnostic analysis methods.It is found that spring precipitation in South China has experienced three stages:during 1960-1971,the precipitation is less than normal;during 1972-1992,it is more than normal;during 1993-2010,it is still less than normal,but the reduction degree is weaker than that in the first stage.There are great differences in the circulation background fields among the different stages of interdecadal variation of spring precipitation in South China.In the first stage,the westerly is flat at 500 hPa,which is not helpful for the north cold air southward.The warm air mass is not active with the anomalous divergence of water vapor flux divergence in South China,so the precipitation is less than normal.In the second stage,the ridge over the north of Tibetan Plateau is stronger at 500 hPa,which is favorable for the north cold air southward.The southward cold air joins the active warm moist air mass in South China,combining with the anomalous convergence of water vapor,thus the precipitation is more than normal.In the third stage,the trough and ridge system of the westerly wind is stronger at 500 hPa,which is good for the northern strong cold air southward.The southern branch trough in the Bay of Bengal fills up,which is not helpful to the southern warm moist air moving to South China.These conditions result in less precipitation in spring.Furthermore,the precipitation in South China has a positive correlation with PDO index.In the view of seasonal changes,there exists the most significant correlation between PDO index in previous autumn and precipitation in South China in spring on the interdecadal time scale.In the view of different stages of interdecadal variation of spring precipitation in South China,the positive correlation of PDO index and spring precipitation in South China is the most obvious during 1960-1971.