雷暴起电和放电物理过程在WRF模式中的耦合及初步检验

Coupling of Electrification and Discharge Processes with WRF Model and Its Preliminary Verification

本文将雷暴云的起电、放电物理过程引入中尺度的WRF(Weather Research and Forecasting)模式,并对超级单体和飑线过程进行了模拟研究。起电过程在Milbrandt双参数微物理方案中写入,包含霰、雹与冰晶、雪之间的非感应起电机制,以及霰、雹与云滴之间的感应起电机制。放电参数化方案只考虑了闪电的整体效应。对一次超级单体的模拟结果表明,电荷结构呈现正、负、正的三极性结构,主正电荷区在-40℃到-60℃之间,主负电荷区在-10℃到-30℃之间,下部正电荷区在零度层附近,总电荷浓度最大值接近2nC/m3。这种电荷结构的垂直分布同以往在强对流天气系统中观测到的典型电荷结构一致。对飑线过程的模拟结果表明,部分单体电荷结构呈现出反的偶极性且飑线中最大电荷浓度小于超级单体。在飑线成熟阶段,模拟得到的闪电分布与观测的地闪活动在分布型上相似。

The processes of cloud electrification and lightning parameterization are introduced into the Weather Research and Forecasting （WRF） model, in which the supercell and squall line are simulated. The numerical formulation of the electrical processes includes the noninductive graupel-ice, hail-ice, hail-snow and inductive graupel-cloud, hail-cloud charge separation mechanisms coupled with the Milbrandt two-moment microphysical scheme. In the mean time, a bulk lightning parameterization is considered in the model. On the one hand, the simulation of supercell produces a normal tripolar charge structure, consisting of a main negative charge region （-10℃ to -30℃） with an upper main positive charge region （-40℃ to -60℃） and a lower positive charge region （near 0℃）. The maximum total charge density is approximately 2 nC/m^3. The simulated vertical profile of charge structure is in accordance with the previous classical structure observed in the severe convective weather. On the other hand, the simulation of the squall line shows the inverted dipolar charge structure in some cells and the maximum total charge density is smaller than that of the supereell. Moreover, the simulated distribution of lightning density is similar to the observed cloud-to-ground （CG）lightning density in the mature stage of the squall line.