地面湿度对雷暴云电过程影响

分析了南京地区2002～2011年(共10年)闪电和地面相对湿度的卫星观测资料,分析表明:闪电密度与相对湿度呈正相关。为了进一步研究相对湿度对雷暴云起电和放电的影响,采用二维雷暴云起、放电数值模式进行敏感性试验。结果表明:随着相对湿度的增大,云滴数目增多,上升风速增强;当相对湿度增加时,较大的上升气流和云水含量有助于产生更大尺寸的冰晶和霰粒子;较大的云滴、霰和冰晶通过非感应起电和感应起电机制促进电荷分离;当相对湿度从60%增加到90%时,总闪数增加,并且只有当相对湿度高达90%时,才能产生地闪。整体而言,相对湿度越大,对流活动更快更强,促进了雷暴云初始起电和放电。

Effects of Relative Humidity on Electrification and Lightning Discharges in Thunderstorms

Ten-year measurements of lightning and relative humidity from 2002 to 2011 have been analyzed in the Nanjing city, China. Statistical analysis shows the lightning density is positively correlated to relative humidity during this period. To further investigate the effect of relative humidity on electrification and lightning discharges in thunderstorms, a two-dimensional cumulus model incorporating dynamics, microphysics, and thunderstorm electrification mechanisms is used to present a sensitive study. The results show that the higher relative humidity in surface leads to more cloud droplet and stronger updraft. Greater updraft and cloud water content primarily contribute to stronger ice crystal and graupel particles production with increasing relative humidity. A greater formation of cloud droplet, graupel and ice crystal result in increasing charge separation via non-inductive and inductive mechanism. The total lightning flashes increase as the relative humidity increase from 60% to 90%, and only tests with high relative humidity of 90% can produce negative cloud to ground (CG) flashes and positive CG flashes. In general, the increase of relative humidity condition generally leads to a quicker and stronger convection, which results in earlier electrification and lightning discharges in thunderstorm.