湖北地区一次雷暴云电荷结构和放电特征的数值模拟研究

在三维强风暴动力—电耦合数值模式中引入非感应起电参数化方案、感应起电参数化方案以及放电参数化方案,对湖北宜昌2014年6月19日一次闪电过程中雷暴云电荷结构和放电特征进行了模拟分析。模拟结果表明,当云内粒子增多、增大,大部分霰粒子逐渐降落到中低层,上部正电荷区减小,底部正电荷堆范围开始扩大,中部负电荷区和底部正电荷区成为主要的起电区域,这种底部正电荷区较厚的三极性电荷结构不利于地闪的产生。在粒子带电分析中,霰与冰晶粒子携带的电荷量均大于云滴,说明霰与冰晶之间非感应碰撞是云中主要的起电过程。虽然云滴的电荷量较小,但霰与云滴之间感应碰撞的作用不可忽视。结合电荷结构的分布,发现底部正电荷堆的垂直分布高度与霰粒子、云滴的电荷浓度的分布有关,且霰与云滴电荷浓度的累积区与底部正电荷堆相一致。

Numerical Simulation of Charge Structure and Discharge Characteristic of a Thunderstormin Hubei Region

Based on three-dimensional dynamic-electrification coupled model which couples the non-inductive electrification parameterization, inductive electrification parameterization and lightning parameterization, a lightning process that occurred on 19 June 2014 in Hubei Province was simulated. According to the simulation results, the charge structure of thunderstorm and discharge characteristic were analyzed. The simulation results show that most of graupel particle will be down the middle and level when the particles increased in cloud, which makes the positive charge diminish in the upper of thunderstorm. But the region of lower positive charge center begins to expand, and the central of electrification region is located between the negative charge space in the middle of cloud and lower positive charge center. The charge structure of bottom-heavy dipole triggers easily IC flashes, and the most discharge characteristic is low IC. In the analysis of particle charge, the graupel and ice crystal quantity of electric charge are higher than cloud droplets, which illustrates the non-inductive collision between graupel and ice crystal is main electrification mechanism. Although the cloud droplets quantity of electric charge is less than other particles, the inductive collision between graupel and cloud droplets make a no negligible contribution to the formation of charge structure. Combined with the distribution of charge structure, the distribution of lower positive charge center have relationship with the charge concentration of graupel and cloud droplets, and the accumulation area between graupel charge concentration and cloud droplets charge concentration is consist with the position of lower positive charge center.