一次河北大暴雨的华北低涡结构和涡度收支分析

Study of the Vortex Structure and Vorticity Budget on a Heavy Rain in North China

利用Micaps系统下常规资料、云图资料和NCEP全球再分析资料,对2004年7月11—12日发生在河北省中南部的一次局地大暴雨个例进行了诊断分析。结果表明:200 hPa西风槽、500 hPa华北低涡和中低层偏东风,是这场暴雨的直接影响系统,该过程中的华北低涡为低层冷心、高层暖心结构,具有随高度向西北倾斜的特征,涡度场特征明显,暴雨区对应着深厚的正涡度区,散度场结构零乱,非高层辐散、低层辐合的配置,暴雨区上空上升运动较强。冷空气来源于500 hPa以下的东北地区,水汽的源地来自渤海,低层偏东风可能是暴雨区所需水汽的主要携带者。水平涡度平流项和水平涡度辐散项作用相反,水平涡度辐散项对总涡度起直接作用且为正贡献,而垂直平流项对总涡度贡献比较小。

Based on routine observations, satellite data in Micaps system and NCEP 1°×1° re-analysis data, a local severe heavy rain occurred in Hebei Province on July 11-12, 2004 was analyzed. The westerly trough at 200 hPa, low eddy in North China at 500 hPa, and easterly wind in middle and lower levels were the direct influence system of the rainfall. The low eddy in North China was a very deep baroelinic system. The three dimensional structure was that the curve of temperature was sunken in the lower level and protuberant in the higher level with the obvious vorticity field characteristics.The rainfall was corresponded with the deep positive vorticity. The disconvergence field was disorder and the upward motion was strong in rainstorm area. The cold air came form northeast area below 500 hPa; the height of convection was lower; the source of vapor was from Bohai Sea and the easterly winds in the lower levels may be the main carrier in transporting the water vapor. In the vortieity budget equation, the horizontal vorticity advection is opposite to the horizontal vorticity diversion which played the main role in the totel vorticity field.