东北冷涡过程对江淮梅雨期降水的影响机制

Analysis of Impacts of Northeast Cold Vortex Processes on Meiyu Rainfall Period over Yangtze-Huaihe River Basin

利用1954—2003年中国740站逐日降水资料以及NCEP/NCAR再分析资料,对东北冷涡影响江淮梅雨的机制进行了研究。结果发现,东北冷涡出现以后,随着它的东移南压与西伸的副热带高压之间相互作用,使我国江淮地区南侧对流层中上层的气压梯度力加强,气压梯度力做功使得动能增大,随后动能向下输送,导致江淮以南地区的西南低空急流形成;低空急流引导的北上暖湿气流与东北冷涡引导的南下干冷空气相互作用,有利于梅雨锋的形成和维持,激发江淮地区低层对流不稳定增加,上升运动出现,从而导致江淮梅雨期降水活跃。

Based on the daily precipitation at 740 stations in China and the NCEP/NCAR reanalysis data from 1954 to 2003, the possible mechanism for the influence of northeast cold vortex （NECV） on Meiyu in the Yangtze-Huaihe River basin is studied. The results show that when the NECV moves eastward and southward, and meanwhile the western Pacific subtropic high extends westward correspond- ingly in the middle troposphere. Interactions between the NECV and the western Pacific subtropical high lead to the enhancement of pressure gradient in the mid-upper troposphere over the southern part of Yangtze-Huaihe River basin, which results in the increase of kinetic energy. Subsequently, the down- ward transfer of the kinetic energy facilitates the formation of southwest low level jet（LLJ） in the low troposphere. The convergence between the warm and wet southwesterly flow induced by the LLJ and the southward dry and cold air from the NECV is favorable to the formation and maintenance of Meiyu front,and the strengthening of convective instability of low troposphere in the Yangtze and Huaihe River basin, which result in ascending motion and active Meiyu rainfall.