中文摘要：

本文基于多套卫星观测数据和ERA-Interim再分析资料,分析了由冬至夏北半球副热带地区大气热源的季节转换特征及其原因。结果表明,北半球副热带大陆东部以对流凝结潜热为主的夏季型大气热源首先于4月初在我国南方地区建立,该过程与江南雨季的形成发展联系紧密。2~3月,江南地区的大气热源以感热加热为主,这时降水以大尺度层云降水为主;而在4月初之后,江南地区降水以对流性降水为主,相应地对流凝结潜热成为大气热源的主要成分。动力和热力诊断分析说明,青藏高原南部热力状况的季节变化是导致4月初江南地区降水性质和大气热源首先发生季节转换的重要原因。2~3月,随着太阳辐射逐渐增强,青藏高原地面感热随之加强,此时对流层中部的纬向西风令江南地区的对流层中部暖平流加强,引起上升运动并加强局地大尺度层云降水,令土壤湿度加大,为随后局地对流性降水的快速发展提供了有利条件。之后,青藏高原地面感热在4~5月期间继续加强,这时高原南坡的＂感热气泵＂令其四周的低空水汽向北辐合,从而加强了江南地区的低空南风,使大量水汽自南海—西太平洋向北输送,令江南地区的对流性降水快速发展,地面感热迅速减小,对流凝结潜热进而成为江南地区大气热源的主要成分。

英文摘要：

Satellite observations and ERA-Interim reanalysis data have been used to investigate the seasonal transition of atmospheric heating source（AHS） in the Northern Hemisphere from winter to summer and its possible causes in the present study. Results show that the earliest formation of summertime diabatic heating occurs over South China in early April, which is closely associated with the development of rainy season to the South of Yangtze River. The sensible heating is dominant in the AHS during February–March when the major component of total rainfall is the large-scale precipitation. After early April, convective precipitation becomes more important, corresponding to increasing importance of condensation heating in the AHS. Diagnostic analysis suggests that seasonal changes in the thermal condition over the southern Tibetan Plateau（TP） are critical for this seasonal transition of the rainfall character and the AHS. During February–March, the sensible heating over the TP is becoming stronger with the enhancement of the solar radiation. The westerlies strengthen the warm advection in the middle troposphere over South China, leading to stronger ascending motions and large-scale precipitation that increase the soil moisture. This is favorable for the subsequent rapid development of local convective precipitation. Further enhancement of surface sensible heating over the TP can make low-level moisture to converge to the north by its ＂air pumping＂ effect during April–May, which intensifies the low level southerly winds. As a result, abundant water vapor are transported from the South China Sea and western Pacific to the South of the Yangtze River, where convective precipitation strengthens and the resultant condensation heating becomes dominant in the AHS.