一次早春中尺度天气过程的分析和预报

Preliminary study of a mesosynoptic case in early spring

本文利用单站自记及常规资料,分析了1987年3月6日造成长江下游部分地区冰雹及大风的一次强对流天气过程。发现浙北及上海南部测站的气压自记曲线均出现4次明显的波动,转换到空间上为平均移速90km/h,具有重力波特征的4个雷暴高压。计算表明,大尺度场上深厚的西南风层,强垂直风切变,高层对流层风的非地转性及其导致的辐散增大,Rossby数>0.45可作为大尺度场的诊断判据。而由稠密地面测站网计算的辐合中心、总能量脊线、风向辐合线等强对流天气的落区及移向的短时预报,都具有重要参考价值。

In this paper, a severe convective system causing hail and gale over some areas of the lower reaches of the Yangtze River on Mar. 3, 1987 is analysed. It has been found that there are four obvious undulations on the barograph trace at the stations of the south suburbs of Shanghai and the northern Zhejiang, which are corresponding to four mesohighs with the characteristics of the gravitational wave at an average speed of 90 km/h by means of a time-to-space conversion.Calculation shows that a deep SW wind layer, strong vertical wind shear, ageostrophic properties in the upper troposphere and Rossby number over 0.45 can be regarded as some diagnostic criteria of the large scale field, moreover, computed convergence center, ridge line of the total energe, convergence line etc. may be significant for nowcastings of the location and direction of the moving severe convective system by use of the data from the denser surface network.