热源异常对2008年初中国南方低温雨雪天气的影响

Impacts of Diabatic Heating Anomalies on an Extreme Snow Event over South China in January 2008

利用资料诊断和全球大气原始方程模式(Intermediate General Circulation Model,IGCM),研究了2008年1月中国南方地区出现罕见的持续性雨雪事件的成因。结果表明,2008年1月大气非绝热加热场的主要异常出现在热带海洋、青藏高原及中亚地区以及北大西洋。用全球异常热源强迫IGCM得到的对流层中低层环流场异常和再分析资料结果十分接近,说明非绝热加热异常和该事件密切相关。分区试验的结果显示青藏高原以及中亚地区的加热异常是导致此次事件的主要原因,中高纬度北大西洋上的海温异常也有一定贡献。前者在中国南方产生了中低层的异常南风气流和贡献率约为95%的异常垂直上升运动,加强了向中国南方的水汽输送;后者加强了北大西洋涛动正位相,能导致12%的垂直运动异常和相对于观测偏弱的环流异常。另一方面,虽然赤道中部太平洋La Ni a事件对应的热汇有利于此次事件的发生,但是热带太平洋La Ni a型海温分布的综合效应对此次事件的贡献为负,贡献率约为-27%。

An extreme event,an unusual snowstorm happening in South China in January 2008,is studied with observational data analysis and numerical modeling experiments.It is found that diabatic heating was centered in the tropical oceans,Central Asia,the Tibetan Plateau,and the North Atlantic Ocean.The results from the numerical experiments demonstrate that global diabatic heating anomalies are responsible for this extreme event.A series of numerical experiments are further designed to identify the key areas where the diabatic heating anomalies occur.The results indicate that the diabatic heating anomalies in Central Asia and the Tibetan Plateau could account for the extreme heavy snow event.Such anomalies generate anomalous air mass rising as well as southerly winds over South China.These features facilitate the water vapor transportation and result in the heavy rain and snow.Meanwhile,an anomalous heating in the North Atlantic enhances the positive phase of the North Atlantic Oscillation,which could contribute to the occurrence of this unusual snow event.On the contrary,a La Nia event happening over the same period,strengthening the heat source in the western Pacific and the heat sink in the eastern and central Pacific,is more likely to counteract the ascent and suppress the rain and snow over South China.