Abstract:Using the NCEP grid 1°×1° data and convection observational data, The vertica l helicity was applied to analyze heavy rainstorm processe, which occurred in Ju ne, 2005 over Guangdong. The results of diagnostic analyses show that both the r apidly strengthening trend of the value in positive center of the vertical helic ity at lower level and the rapidly lessening trend of the negative one at upper level during the rainstorm can reflect the position and intensity of the heavy r ainstorm in Guangdong. When the value in negative center of hp at upper level ra pidly reduced and the positive one at lower level rapidly increased, and when th e region of both the positive helicity center turning strong and the negative on e turning poor overlapped near t he same longitudeor latitude, the rainfall over the corresponding region reached the maximum and the intensity of the rainstorm reached the strongest. During the heavy rainfall which is never suffered in a c entury in Longmen and the most heavy rainfall days in Guangdong, positive vertic al helicity center at the lower level troposphere and negative one at the uppe r troposphere tends downwards to the low level.