Preliminary study of a mesosynoptic case in early spring

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.

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