气溶胶对雷暴云起电以及闪电发生率影响的数值模拟

A Numerical Study of Aerosol Effects on the Electrification and Flash Rate of Thunderstorms

本文利用二维耦合气溶胶模块的雷暴云起电模式，结合一次南京雷暴个例，进行250 m分辨率雷暴云起电模拟实验，探讨了气溶胶浓度对雷暴云空间电荷分布以及闪电发生率的影响。在这个气溶胶模块中，假定一个三模态的气溶胶对数分布，考虑了气溶胶活化过程。结果显示：（1）随着气溶胶浓度增大，雷暴云电荷结构保持为三极型。（2）当气溶胶浓度从50 cm^-3增加至1000 cm^-3时，水成物粒子浓度上升，雷暴云电荷量和闪电发生率增加明显。（3）气溶胶浓度在1000～3000 cm^-3范围时，云水竞争限制了冰晶的增长，导致雷暴云上部主正电荷堆电荷量降低。云滴和霰粒子浓度缓慢上升促进中部主负电荷堆和底部次正电荷堆电荷量继续增大。闪电发生率保持稳定。（4）当气溶胶浓度大于3000 cm^-3时，水成物粒子浓度稳定，云内的电荷量以及闪电发生率保持为一定量级。

AbstractA two-dimensional cumulus model coupled with an aerosol module is used to simulate a case of tropical convection in Nanjing. Numerical simulations at a resolution of 250 m are performed to investigate the effect of aerosol concentration on the electrification and lightning flash rate in the thunderstorm clouds. In this aerosol module, the distribution of aerosol particles is fitted by superimposing three log-normal distribution functions, and the activation of aerosol particles to form cloud droplets is considered. The results show that： （1） The charge structure in the thundercloud remains a triple charge structure as the aerosol concentration increases. （2） When the aerosol concentration is changed from 50 to 1000 cm^-3, a stronger formation of cloud droplets, graupel and ice crystals results in an increasing charge separation and lightning flash rate. （3） In the range of 1000–3000 cm^-3, the decrease in ice crystals caused by vapor competition leads to a reduction in upper positive charge, while the enhancement of graupel and cloud droplets results in the contribution of inductive charge to the middle negative charge region and lower positive charge region increasing with greater aerosol concentration. The flash rate shows a slight change. （4） At very high aerosol concentrations （above 3000 cm^-3）, the magnitude of the charge and lightning flash rate, which remains steady in the thundercloud, is insensitive to aerosol concentration.