THE HELICITY ANALYSIS OF MEI-YU FRONT STORM RAINFALL DURING JULY, 1991

In this paper, the evolution of the helicity during the period of Mei-yu of July. 1991, is analyzed. The results show that the evolution of helicity is a indicator of storm rainfall in a certain sense. And the horizontal distribution of the z-helicity is corresponding to the storm rainfall region properly in the middle and lower troposphere (below 500hPa).The vertical structure of z-helicity above the precipitation center is advantageous to the maintenance of the storm rainfall. The effect of this kind of structure is called "dynamic flywheel"