重庆地区一次雷暴云电过程及其对初始云滴数浓度响应的数值模拟

采用耦合了Saunders和Takahashi两种非感应起电参数化方案的RAMS(Regional Atmospheric Modeling System)模式,对重庆地区一次雷暴过程进行模拟,对比分析了两种起电参数化方案下,电荷开始分离时和雷暴云发展到成熟阶段时的水成物粒子的分布、所带电荷密度以及雷暴云的电荷结构分布。模拟结果表明,在Saunders起电参数化方案下,雷暴云的电荷结构从起电到放电都呈现偶极性特征,而在Takahashi参数化方案下,雷暴云的电荷结构则由反偶极性发展成正偶极性。为研究CCN(cloud condensation nuclei)对雷暴云的影响,本文进行了两组敏感性试验,随着云滴初始数浓度增加,雷暴云的电荷结构没有发生极性翻转,但雷暴云中电荷量增加,电荷分布区域变大,有利于闪电发生。在Saunders起电参数化方案下,当云滴初始数浓度大于2 000 cm-3时,电荷量变小。通过分析微物理量场和微物理过程发现,随着云滴初始数浓度增加,冰相粒子质量混合比增加,在Saunders起电参数化方案下,当云滴初始数浓度大于2 000 cm-3时,霰粒子质量混合比减小。验证了CCN的变化能影响云的微物理过程,从而影响雷暴云的电荷分布以及闪电的发生,尤其是冰相物质的变化显著影响了雷暴云的起电过程。

A numerical simualtion on a thunderstorm in Chongqing and its response to changes in initial number concentration of cloud droplets

In this paper,RAMS(Regional Atmospheric Modeling System) model,coupled with two non-inductive charging parameterization schemes(Saunders and Takahashi schemes),is adopted to stimulate a thunderstorm occurred in Chongqing.A comparative analysis of two schemes is presented on the distribution of hydrometeor particles,the charge density and the distribution of charge structure in the thunderstorm when the charges start to separate and the thunderstorm reaches its maturity.Simulation results show that a dipole characteristic is presented from electrifying to discharging in the charge structure with Saunders scheme,while the characteristic in the charge structure switches from inverse dipole to positive dipole with Takahashi scheme.To study the impact of CCN(cloud condensation nuclei) on the thunderstorm,two sets of sensitivity tests have been carried out.As the initial number concentration of cloud droplets increase,no polarity conversion occurs in the charge structure,however,in the thunderstorm,the charge amount increases and the distribution area of charge expands,which is conductive to the occurrence of lightning.With Saunders scheme,the amount of charge decreases when the initial number concentration of cloud droplets is over 2 000 cm^-3.Through analysis of the microphysical field and microphysical process,it is found that the mass mixing ratio of ice-phase particles increases as the initial number concentration of cloud droplets increases,while the mass mixing ratio of graupel particles decreases when the initial number concentration of cloud droplets is over 2 000 cm^-3,with Saunders scheme.This verifies the impact of CCN variation on the microphysical process,thus further on the distribution of charge in the thuderstorm and the occurrence of lightning,especially the impact of variation of ice-phase materials on the electrification process of thuderstorm.