减弱对流云降水的AgI催化原理的数值模拟研究

在对流云模式中增加了AgI两个预报量,耦合了考虑受水汽过饱度和温度影响的4种核化机制的AgI催化模块,使其具备了对AgI类催化剂的模拟能力,能够研究AgI类催化剂对对流云系统的影响。利用该模式对一次华南对流云降水过程进行了AgI催化数值模拟试验,对人工减缓对流云降水的可能性及原理进行了研究。模拟结果表明,在适当的时机对适当的部位进行大剂量的催化,可以减少总降水量,也可以减少最大降水中心的雨强。当催化浓度达到2×10~8 kg~(-1)时,可以减少32%的降水量,具备有效减缓对流云降水的可能性。大剂量催化后,大量的AgI粒子在冷区核化后,消耗了大量的过冷水。催化后霰粒子的落速和雨水的落速减小。催化阶段由于霰融化成雨水减少而使降水减弱。催化结束后在霰融化成雨水增多的情况下,雨水的蒸发大幅增加,从而导致了降水量的持续减少。AgI在模拟的强对流云中主要以受过饱和度影响的凝结冻结和催化剂长时间作用的浸没冻结这两种方式成核。研究所用催化方法在外场作业中具有技术可行性。

Numerical study of the AgI seeding principle for decreasing the convective cloud rainfall

After two prognostic variables are added, an AgI seeding scheme is coupled with the three-dimensional cloud model, considering four nucleation modes. A case of convective cloud rainfall is simulated using this model. Numerical seeding experiments of releasing AgI in cloud are simulated to study the possibility to decrease the convective rainfall intensity. Several tests in the different locations and different concentrations of seeding particles are designed. The results show that overseeding in updraft area with supercooled water can not only reduce the amount of rainfall, but also reduce the maximum rainfall strength. With 2×10⁸ kg^-1 seeding concentration, rainfall amount can be decreased up to 32%, which greatly lowers the possibility of causing flood. After seeding with large amounts of AgI, numerous AgI particles are nucleated, and these ice particles consume most supercooled water. The falling speeds of graupel and raindrops become weaker after seeding. The decrease of melting amount of graupel to rain in seeding cloud causes the decrease of rain amount, but later the much more evaporation of rain causes less rainfall amount. The results show that the condensation freezing and immersion freezing are the dominant nucleation modes in this convective cloud. The over-seeding methods in this research are able to be used in field operation.