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为了验证雷暴单体中是否会由于降水退屏蔽作用导致正地闪的发生,建立了典型的雷暴云三极性电荷结构模型,利用现有的闪电放电参数化方案,通过改变中负和下正电荷区的高度和电荷密度进行的对比试验,对雷暴单体中降水退屏蔽作用和正地闪发生之间的关系进行研究.结果表明,在雷暴单体中发生降水时,引起的雷暴云中负和下正电荷区高度下降以及电荷密度的减小会使雷暴云中电场和电势的分布发生变化.当中负和下正电荷区的高度降低时,模拟域内最大电场强度降低,最大电场强度处电势增大,最大电场强度处和地面之间电势差增大,使正先导更容易发展到地面形成正地闪.当中负和下正电荷区的电荷密度减小时,模拟域内最大电场强度降低,最大电场强度处电势的绝对值先减小后增大,在电势增大过程中最大电场强度处和地面之间电势差增大,正先导也更容易发展到地面形成正地闪.因此,雷暴单体中降水退屏蔽作用对正地闪的发生是有利的.“,”In order to understand if precipitation shielding can cause positive Cloud-to-ground (CG) lightning flashes in thunderstorm cell,a normal tripole charge structure model of thunderstorm,including lightning discharge parameterization,was established and used to study the relationship between precipitation shielding and positive CG lightning flashes in thunderstorm cell through changing altitudes and densities of middle negative and lower positive charge regions.The results indicate,when precipitation occurs in thunderstorm cell,the altitudes and charge densities of the middle negative and lower positive charge region will decrease,which will change the distribution of spatial electrical field and potential and then triggered lightning.When the altitudes of the middle negative and lower positive charge region decrease for the reason of downward flow caused by precipitation,the maximum electrical field strength will decrease and its correspond electrical potential will increase,thereby,the electrical potential difference between the point of the maximum electrical field and ground surface will increase,the positive leader is easier to reach the ground to form positive CG lightning flashes.And when the charge densities of the middle negative and lower positive charge region decrease for the reason of the electric charge adhere to precipitation fell out of the cloud,the maximum electrical field strength will decrease and its correspond absolute value of electrical potential will decrease first and then increase.During the absolute value of electrical potential is decreasing,which is negative and its orientation is vertical upward.It is of course impossible to produce a positive CG lightning flash.But when the densities of middle negative and lower positive charge region decrease to a certain degree,the value of the electrical potential will be positive and its orientation is vertical downward.Then the value of the electrical potential will keep increasing.The electrical potential difference between the point of the maximum electrical field and ground surface will increase too,the positive leader is easier to reach the ground to cause positive CG lightning flashes.So,the hypothesis that precipitation shielding can cause positive CG lightning flashes is reasonable in thunderstorm cell.