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

Numerical Simulation of Charge Structure and Discharge Characteristic of a Thunderstorm in Hubei Region

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。

Based on the three-dimensional dynamic-electrification coupled model which couplesthe non -inductive electrification parameterization, inductive electrification parameterization andlightning parameterization, a lightning process occurred on June 19th, 2014 in Hubei Province wassimulated. According to the simulation results, the charge structure of the thunderstorm and itsdischarge characteristic were analyzed. It is showed that, most of graupel particle move downwardgradually to the middle and low level when the particles increased in both amount and size in cloud,which makes the positive charge diminish in the upper of thunderstorm, while the region of lowerpositive charge center begins to expand, and the negative charge space in the middle level as wellas the positive charge space in the lower level in cloud in hence became the dominantelectrification region. Such charge structure with bottom-heavy dipole triggers easily IC flashes, andthe most discharge characteristic is low IC. In the analysis of particle charge, the graupel and icecrystal quantity of electric charge are higher than cloud droplets, which illustrates the non-inductivecollision between graupel and ice crystal is the main electrification mechanism. Although the clouddroplets quantity of electric charge is less than other particles, the inductive collision betweengraupel and cloud droplets makea no negligible contribution to the formation of charge structure.Combined with the distribution of charge structure, the distribution of lower positive charge center isrelatted to the charge concentration of graupel and cloud droplets, and the accumulation areabetween graupel charge concentration and cloud droplets charge concentration is consist with theposition of lower positive charge center.