Analysis of helicity in a rainstorm in north China

In this paper,a rainstorm in north China was simulated by the ARPS model and the establishment and development process of its helicity was analyzed in detail.Results show that the understanding of the configuration of helicity in low level and high level is helpful to analyzing the occurrence and development of the convective systems and obtaining the location of the precipitations.Area having positive values within xy-helicity front is in favor of the occurrence of the rainstorms,but its displayed range is usually larger than that of the actual precipitation.At high level,the obvious increase of the negative z-helicity indicates the stronger development of the convective systems and more rainfall;while at low level,about 3.25km in height,the central areas of the positive z-helicity usually agree well with the precipitations.Compared with xy-helicity,z-helicity is more accurate in locating the rainfall range,and thus is a better parameter indicating the maintenance,development and the intensity of a rainstorm system.