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.