霰粒子参数对强对流云降水和催化影响的数值模拟研究

本文利用三维对流云AgI催化模式, 开展了霰粒子密度和落速参数的敏感性模拟试验, 以研究高凇附度时霰粒子参数的选取对催化模拟结果的影响。敏感性试验中对七个霰微物理过程进行了调整。分析发现改变霰落速参数和霰密度, 可以引起3小时模拟的总降水量增加4.9%。催化后改变了敏感性试验中霰落速和上升气流的配置, 并影响到霰碰并云水和冰晶的过程, 及霰融化成雨水的过程。在高凇附度云中如果只增加霰密度而没有增加相应的落速系数, 将使云中霰含量大幅增加。霰参数也影响了自然云和催化云的降水效率。过量催化使得催化云的降水效率低于自然云。增加霰密度的同时也增加霰落速系数, 将使其降水效率高于对照试验, 从而影响催化效果。在高凇附度云中采用大密度和较大下落系数, 并且利用比数浓度平均落速计算霰粒子比数浓度的下落过程, 会使催化效率从25%减少到15%, 极大地改变催化效果。所以在高凇附度的暴雨个例中, 应当采用高霰密度和相应的高霰落速, 否则减雨的催化效果将会被大幅夸大。

Numerical Simulation Study of the Impacts of Graupel Parameters on Strong Convective Rainfall and Seeding Effects

By using a three-dimensional convective cloud model with the AgI seeding scheme, sensitivity simulations are conducted with various graupel densities and fall velocities. These parameters influence seven microphysics processes of graupel particles. Numerical simulations show that these parameters affect rainfall amount as much as 4.9%. The relationship between graupel fall velocities and wind updrafts are modified after seeding, and the values of collection of cloud water by graupel, collection of ice by graupel, and melting of graupel to rain water are influenced. When increasing only graupel density, graupel mixing ratios are increased significantly. Graupel density and fall speed parameter also change the rainfall efficiency of both seeding and natural clouds. Increasing the graupel density along with the fall velocity parameter results in relatively high rainfall efficiency, and their seeding effects are only 15% rather than the 25% noted in control seeding simulation. Therefore, in the simulation of the rime density of convective clouds, both the graupel density and fall velocity parameter should be increased; otherwise, the seeding effect will be significantly enlarged.