By using the data of synoptic charts and Datong Doppler radar data,two heavy snow processes in Datong during November 9-10,2009 and on March 14,2010 were analyzed. The results show that surface current,occluded fronts,high-altitude and low-altitude jet stream were main reasons for the heavy snow processes. Zero velocity curves were like " S" at elevations of 0. 5,1. 5 and 2. 4°,and there were a pair of " bull's-eye" structure,showing that heavy snow would occur. As for the two heavy snow processes,the qualitative judgment results based on the area of positive and negative velocity zones were consistent with the quantitative analysis results based on the average divergence well,so we can use radar images to judge features of velocity fields rapidly in practice.
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