Diagnosis of vertical helicity, divergence flux and their extensions in heavy-rainfall events

On the basis of vertical helicity, we define three parameters, namely, the divergence flux, moisture vertical helicity and moisture divergence flux. The parameters are calculated with NCEP/NCAR real analysis data in the two heavy-rainfall events occurring in China. The result shows that the parameters are closely related to the precipitation systems since they are capable of describing the typical vertical structure of dynamical and moisture fields. The anomalies of the parameters vertically integrated well correspond with the observed 6h-accumulated surface rainfall. This suggests that the parameters are capable of predicting and indicating the development and propagation of precipitation systems. The calculation with the 6-hour forecasting data of NCEP-GFS shows that the parameters have the ability of predicting precipitation and the moisture divergence flux is significantly beller than the other parameters in predicting precipitation.