雷暴单体的对流强度对电荷结构的影响

摘要

A three-dimensional dynamics-electrification coupled cloud model is used to investigate the relationship between the charge structure and convection strength of a thunderstorm cell,by changing the potential temperature in the center of disturbance region and conducting sensitivity tests.Results show that the convection strength of the thunderstorm cell increases with the potential temperature disturbance and affects the spatial charge structure,but there is always a lower positive charge region.When the convection is weak,the charge structure within the thunderstorm is simple,comprising only a main negative charge region and lower positive charge region,without an upper main positive charge region.In the medium-intensity convection thunderstorm,the charge structure basically presents the normal tripole structure,and the main negative area has upper and lower two charge centers,and charge density of the upper center is larger.In addition to the main negative charge,upper main positive charge and lower positive charge regions in the strong thunderstorm cell,there is a small-range weak negative charge region under the lower positive charge region and a negative screening layer on top of the cloud.The charge structure is relatively complex,having five vertically stacked regions of charge with alternating polarity.That is because that the negative ions in the clear air attracted downward to the cloud boundary are attached to particles to form the negative screening charge layer at cloud top.Meanwhile,owing to the strong convection,graupel particles grow more rapidly,solid precipitation increases,and a short-lived weak negative charge region beneath the lower positive charge region is formed by graupel in the downdraft through the inductive collision with cloud droplets.%利用三维雷暴云动力-电耦合数值模式,通过改变中心扰动位温,设置敏感性试验组,分析探讨雷暴单体对流强度对电荷结构的影响.结果表明:雷暴单体对流强度随着扰动位温的增加而增加.对流强度不同,其空间电荷结构也明显不同,但始终存在底部次正电荷区.当对流较弱时,雷暴电荷结构简单,只有主负电荷区和次正电荷区,无主正电荷区.在中等强度的对流雷暴中,雷暴内基本呈正常三极性电荷结构,且主负电荷区有上、下两个明显的电荷中心,上部中心的电荷密度更大.在强雷暴单体中,除了正常的三极性结构以外,次正电荷区以下出现了小范围弱的负电荷区,云顶出现了负屏蔽层,从下到上呈现出正负交替的五层,是电荷结构最复杂的阶段.这主要是由于云上部的正电荷区持续时间较长,电荷密度较大,增强了对周围大气中自由离子的吸引,自由离子被吸引到云边界附着到粒子上,在云顶形成了负屏蔽电荷层.同时,由于对流强,霰粒子可以得到更快的增长,固态降水增强,下沉气流中的霰通过与云滴的感应碰撞形成了云底部短时的弱负电荷区.