摘要
文中分析了 1998年 7月 2 0～ 2 3日发生于长江流域的持续性降水和暴雨过程 ,在分析大尺度降水和中小尺度暴雨相对应的环流场和天气实况的基础上 ,主要分析相应大气层结的对流不稳定和条件性对称不稳定条件 ,并对切变线上涡层不稳定做了重点介绍和分析 ,计算了条件性对称不稳定判据和涡层不稳定判据。结果表明 :降水期间大气低层有对流不稳定和对称不稳定能量的积聚 ,在这两类不稳定条件都基本满足的情况下 ,涡层不稳定的维持对此次降水过程中暴雨的发生提供了有利的不稳定环境场 ,具体的计算分析还表明环境场的配置制约着切变线上低涡扰动的发展 ,是造成降水的重要原因之一。
In this paper,the torrential rain occurring over Yangtze River Basin in 20-23July 1998 is analyzed. Based on circulation and weather events corresponding to large-scale precipitation and meso-microscale torrential rain, convective instability and conditional symmetry instability in atmosphere are analyzed, the criteria of symmetry instability as well as vortex sheet instability are colculated and analyzed. Analyses of the convective instability and conditional symmetry instability indicate that the convective instability provides instable energy for the torrential rain, and energy of conditional symmetry instability also accumulates at 925-1000 hPa during the rainfalls. Because the criterion of the conditional symmetry instability is not satisfied above 700 hPa for all rainfall regions, it is not enough to explain the formation of the torrential rain if the conditional symmetry instability itself is considered. The torrential rain did not always occur in the areas where the criterion of convective instability and conditional symmetry instability are satisfied. On the condition of convective instability and conditional symmetry instability, it is easy to explain the torrential rain over Yangtze River Basin with the theory of vortex sheet instability. Calculation of the prerequisite of vortex sheet instability also indicates that vortex sheet instability is an important factor contributing to the torrential rain over the Yangtze River Basin in 20-23 July 1998. All results manifest that under the condition that convective instability and conditional symmetry instability are in existence, maintenance of vortex sheet instability provides favored circumstance for the torrential rain. Material calculation also indicates that the disposition of environment field restrains the vortex development along shear line, which is an important factor to precipitation over the Yangtze River Basin.
出处
《气象学报》
CAS
CSCD
北大核心
2003年第3期323-333,共11页
Acta Meteorologica Sinica
基金
中国科学院知识创新工程项目(KZCX3 SW 213)
中国科学院KZCX2 2 0 8项目
关键词
长江流域
暴雨
非线性不稳定条件分析
降水过程
Torrential rain,Convective instability, Symmetry instability, Vortex sheet instability
