A Numerical Study Of A Thunderstorm In Chongqing And Its Response To Changes In Initial Concentration Of Cloud Droplet

In this paper, Model RAMS(Regional Atmospheric Modeling System), coupled with two non-inductive electric parameterization schemes---Saunders and Takahashi, is adopted to stimulate a thunderstorm occurred in Chongqing on July15th,2010.Firstly, a comparative analysis, in the two electric parameterization schemes, is performed on distribution of hydrometeors particles, charge density and distribution of thundercloud charge structure when the charge separation starts and the thundercloud develops to a mature stage. The simulation results show that the charge structure with positive dipole emerges in both schemes when the thundercloud develops to a mature stage. In Saunders scheme, dipole characteristics is presented in thundercloud charge structure from charging to discharging, while the thundercloud charge structure, in Takahashi scheme, switches from inverse dipole to positive dipole.Secondly, this paper presents the impact of cloud droplet number concentration on thundercloud charge. Sensitivity tests show that by increasing the initial concentration of cloud droplets, cloud droplets and polymer particles increased, and graupel particles increased first, then changed slowly and decreased afterwards. No polarity conversion occurred in the thundercloud charge structure, however, the amount of charge also increased first, then changed slowly and decreased afterwards. By analyzing the microphysical field and microphysical process, it is found that the mass mixing ratio of ice-phase particles improves as the initial concentration of cloud droplets increases.Finally, the paper comparatively studies the impact of changes in cloud droplet number concentration on thundercloud. In Saunders scheme, better consistency is presented in changes of the amount of charge and that of graupel particles. In terms of the spatial distribution of the charge, in Takahashi scheme, the distribution of graupel particles and the charge presents a better consistency in the horizontal direction, however, in Saunders scheme, the distribution of graupel particles and the charge presents a better consistency in the vertical direction. In Saunders scheme, both the amount of charge and the mass mixing ratio of graupel particles decreases when the initial concentration of cloud droplets is over2000cm"3. This verifies the impact of CCN variation on microphysical process, thus further on the distribution of thundercloud charge and the occurrence of lightning, especially the impact of variation of ice-phase materials on the electrification process of the thundercloud.