【摘要】 选取2003年藏北高原那曲地区的两次典型过顶雷暴过程,首先总结了它们的层结特征,然后利用一个只考虑感应和非感应起电机制的三维强风暴动力和电耦合模式模拟了两次雷暴过程的电荷结构,最后从微物理场和流场出发讨论了高原雷暴电荷结构特征及其主要形成原因。结果表明,由于高原平均地表温度较低,雷暴云反转温度层以下的起电区域较小,强的垂直上升速度使大粒子能够到达较高的高度,增加了大小粒子碰并几率,易形成明显的三极性电荷结构特征;较弱的上升速度易使大小粒子比含水量中心受重力作用过早的分离,高层的小粒子和低层的大粒子基本不参与起电活动,云底部和上部的正电荷区减弱。更多还原

【Abstract】 Due to Nagqu’s unique geographical situation,dominated by large plateaus,valleys and basins which average altitudes are 4-5 km MSL,the thundercloud activity in the Qinghai-Xizang Plateau is particular.The characteristics of soundings in two thunderstorm days in Nagqu are analyzed.As the altitude of Nagqu is about 4.5 km MSL,the average surface temperature is 15.7℃,which is lower than Chinese inland plateau and littoral.The thickness between 0℃ and-20℃ levels is about 2.93 km.The average heights of cloud-base and top are 5.7 km and(12.2 km) MSL,respectively.On the average,CAPE(convective available potential energy) is critical instability(0-1000 J/kg).The mean relative humidities in the middle and upper levels are 62.1% and 43.5%,respectively.The high humidity and dynamic force can provide the favorable conditions for the formation of line storms or MCSs.The characteristics of charge structure in thunderstorm of Nagqu are analyzed by using the three-dimensional dynamic-electrification coupled model.This model only includes inductive and non-inductive charging mechanisms.Two thunderstorms are simulated.The result shows that the charge region under the temperature reversal is limited,because the surface temperature is lower in Nagqu.The mean duration of solid particles in strong updraft is longer than in weak updraft.Collision probability between big and small particles is increased in strong updraft,so it is easy to form tripole charge structure.The centers of specific water content of big and small particles are separated early in weak updraft.The small particle in the upper layer and big particle in the lower layer hardly take part in charge activity,so main positive charge region and LPCC(lower positive charge center) is small.On the average,LPCC is located in downdraft,while main positive charge region is located in updraft.Main negative charge region is distributed about zero vertical velocity.It is easy to form several alternate negative and positive charge layers in strong updraft.更多还原