Produce Disastrous Gale Strong Storm Formation Mechanism And Numerical Simulation Study

In this study, the mechanism of the severe convective storm accompanied with severe wind was investigated using both MM5 and a hail-bin cloud model. A severe convective storm accompanied with severe wind, heavy rain and hail on 23 August 2001 in Beijing was simulated by MM5 initiated with NCEP reanalysis data and a three-dimensional cloud model with hail-bin microphysics, which was initiated with the air soundings at Beijing at 20:00 on 23 August 2001, and some comparisons were also made between the simulated and natural storm.It showed that MM5 could well simulate the mescoscale background field and the occurrence and development of the convective storm. But the values of the simulated updraft and downdraft, especially downdraft, were much smaller than that observed due primarily to the large grid size that MM5 has. The three-dimensional cloud model with hail-bin microphysics could simulate the characteristics of the severe storm such as life cycle, rainfall distribution and diameter of hail well, and also could produce strong downdraft and wind shear (downburst).The mechanism of the downburst formation was also investigated based on the cloud microphysics of the simulated storm and it was found that this downburst was primarily produced by hail loading, and enhanced by hail melting and rain evaporation. And the loading and the melting of hail played a very important role in producing the downburst. The gale at the surface was caused by the severe downburst.