Numerical study of the influence of the latent heat on the mesoscale convective system and precipitation during a torrential rain event in North China.

A mesoscale convective system which produces torrential rainfalls on 22-24 July 2005 in North China is selected as a research case. This rainfall process is reproduced successfully by the ARPS model. On the base of the analyses of the cloud field, the dynamical field and the vertical distribution as well as the function characteristics of the latent heat released by the microphysical processes, the influence of the latent heat on the development, evolvement, dynamical field, water vapor field and rainfall of the cloud system is studied and analyzed via changing the latent heat of the main microphysical processes for conducting the sensitivity experiments. Finally, the impacting passes of the latent heat in the warm zone of the cloud is summarized. The results show that the microphysical processes play a heating up role over the 5000 m height and a cooling one under this height and the impacting levels of the latent heat of different microphysical processes are different: the vapor condensation, initial formation of cloud ice, sublimation of snow and accretion of graupel play the heating role in the upper level, the vapor condensation/graupel melting have a heating/cooling role in the middle level, and the diabatic cooling effect in the low level is mainly produced by rain evaporation. The latent heat has an important role on development processes of the cloud system and precipitation, and on the dynamical field and thus on the water vapor field, cloud field and rainfall. When cooling effect of graupel melting is ignored, which is corresponding to increasing latent heat in the warm zone of the cloud, it is propitious to form the cyclonic circulation in the low level and increase the convergence area and intensity of vapor flux. Therefore, it accelerates the development of the convective cloud system, expands the heavy rain region and increases obviously the precipitation amount. If the vapor condensation latent heat is decreased by 20%, the development of the cloud system is restrained evidently and the cyclonic circulation is not formatted in the low level. As the same time, the convergence area is decreased and the convergence of the vapor flux is lowered and, the water content in the cloud and the rainfall are all decreased. Moreover, the latent heat has an effect on the development and evolvement process of the mesoscale convective system and it changes the conformation of the cloud system, its movement and the intensity and the distribution of the convective cloud clusters.