一次暖云降水主导的暴雨过程中电荷结构特征及其成因的模拟研究

为了认识以暖云强降水为主导的对流单体中的电荷结构特征及其形成原因, 利用加入了起放电参数化方案的WRF模式, 模拟了2017年5月7日广州局地突发的以暖云降水为主导的特大暴雨过程, 分析讨论了此次过程中一个单体成熟发展阶段的电荷结构的特征及其成因。结果表明, 此次以暖云降水为主导的特大暴雨过程中的单体对流强度较弱, 云顶高度低于同地区典型对流过程, 强回波区由大雨滴形成, 范围较小, 顶较低, 对流运动向0℃层以上输送的过冷水较少, 不利于冰相粒子形成, 导致大小冰相粒子含量均较少, 其中含量最多的冰相粒子为雪花, 其次依次为霰、冰晶、冰雹。云内起电较弱, 以非感应起电为主。非感应起电主要以对流区中-15℃层以下正的起电率为主, 感应起电率以对流区中的负极性为主。对流区中空间净电荷呈三极性结构, 其中中部负电荷区和底部正电荷区中心电荷密度及电荷区范围相当, 上部正电荷区相对较弱, 范围较小。对流区外围仅有弱的中部负电荷区和底部正电荷区。中部负电荷区由带负电荷的冰晶和雪花共同主导, 上部正电荷区由带正电荷的雪花主导, 底部正电荷区主要是由带正电荷的霰粒子及带正电荷的雨滴主导。强起电区和放电区重合, 主要集中在回波中心上部35~50 dBZ的对流区。 

SIMULATION STUDY OF CHARACTERISTICS AND CAUSES OF CHARGE STRUCTURE IN RAINSTORM DOMINATED BY WARM CLOUD PRECIPITATION

In order to understand the characteristics and causes of charge structure in convective cells dominated by warm cloud precipitation, WRF model with electrification and discharge parameterization scheme is used in this study to simulate the sudden rainstorm dominated by warm cloud precipitation in Guangzhou on May 7, 2017, and analyze the characteristics and causes of charge structure of a monomer in this process. The results show that the height of the cloud top during the extreme rainstorm dominated by warm cloud precipitation is lower than that in a typical convective process in the same area, and the convection intensity is weaker. The strong echo area consists of heavy raindrops, with a smaller range and a lower top. There is less supercooled water transported above the 0 ℃ layer, which is not conducive to the formation of ice phase particles. Therefore, in the monomer maturation stage, the proportion of small and large ice particles is small, among which most are snowflakes, followed by graupels, ice crystals, and hail. The electrification in the cloud is weak with non-inductive electrification as the dominant. The noninductive electrification is mainly positive below-15 ℃ in the convection zone, and the inductive electrification shows negative polarity in the convection zone. The net space charge in the convection zone has a tripolar structure. The density and range of charge in the middle negatively charged region and the positively charged region at the bottom are similar; the main positively charged region is relatively weak with a small range. There is only a weak negatively charged zone in the middle and a positively charged region at the bottom of the periphery of the convection zone. The middle negatively charged region is dominated by negatively charged ice crystals and snowflakes, the upper positively charged region is dominated by positively charged snowflakes, and the positively charged region at them bottom is mainly dominated by positively charged graupel particles and positively charged raindrops. The strong electrification zone and the discharge zone overlap, mainly concentrated in the convection zone of 35—50 dBZ above the echo center.