梅雨锋上引发暴雨的低压动力学研究

A Dynamic Study of One Kind of Meiyu Front Lows Producing Heavy Rainfall

对 1 998年“二度梅”结束前后长江中下游地区准静止锋上一次气旋发生发展过程进行了涡度收支的诊断分析。结果表明 :( 1 )风场 (尤其是辐散风场 )对该气旋发生发展有重要影响 ;( 2 )低层辐合场是直接决定气旋发生发展的动力因子 ,它导致低层正涡度制造 ,对气旋的发展起直接作用 ;( 3)涡度平流上正下负的配置和水汽凝结潜热释放 ,通过影响上升运动及低层辐合对地面气旋的发展起间接作用。在系列研究工作的基础上 ,提出了梅雨锋上第二类气旋 (低压 )

Vorticity budget was diagnosed during the developing process of a cyclone which occurred on Meiyu (Baiu)front around the end of the second stage of Meiyu (Baiu) in 1998. It was found out that it is different not only from the classical Euramerican cyclone models, but also from the mesoscale lows which usually occur during Meiyu (Baiu) period. It belongs to another kind of cyclone on Meiyu (Baiu)front. Its characteristics are as follows: (1) Wind is the major feature of this cyclone. (2) From the results of the budgets of vorticity, two different factors influenced the development of the cyclone: one factor, the low\|level convergence field directly determined the occurrence and development of the cyclone. It created low\|level positive vorticity and had direct effects on the development of the cyclone; the other factor, the positive horizontal advection of vorticity in mid\|and upper troposphere and the whole\|level vertical advection of vorticity had indirect effects on the development of the cyclone through the low\|level convergence. (3) Based on a series of research work, including this paper, a physical model of one kind of cyclones on Meiyu front has been suggested.