一次层状云降水过程微物理机制的数值模拟研究

Simulation of the Stratiform Cloud Precipitation Microphysical Mechanism with the Numerical Model

层状云由于在水平上较为均匀,可以用一维模式来模拟其云微物理过程。因此,本文使用一个包含详细微物理过程的一维层状云分档模式结合地面Doppler雷达、PMS观测资料,对2007年7月1日吉林省一次锋面抬升引起的层状云降水系统进行了模拟研究。计算结果详细地刻画了水滴、霰、雪花和冰晶粒子谱分布、含水量在垂直高度上的分布与变化,并定量分析了该例中冰晶层、混合层和暖层中凝华、凝结、碰并等微物理过程对粒子谱型的影响,以及冰晶层、混合层和暖层对地面降水的贡献率。结果表明,在该例中,冰晶层对混合层的播撒以直径D<300μm的小冰晶粒子为主。从混合层播撒D>100μm的水滴粒子以及未完全融化的冰晶粒子对暖层中小云滴粒子的碰并收集作用较强,同时,一部分降水粒子在暖层内可通过随机碰并机制产生。三层云对降水的贡献分别为3.5%、38.5%和58%。三层云中若缺少混合层,地面降水仅为0.475mm/h,谱宽920μm,且雨滴粒子数浓度较高;若无暖层,降水时间滞后,雨强增加缓慢,地面降水达0.807mm/h,雨滴粒子谱宽达1500μm;无冰晶层时,降水强度与三层俱全时的模拟结果基本一致,降水及雨滴谱的改变非常微弱。

The stratiform cloud can be simulated with a one-dimensional model,duo to its uniform horizontal distribution of physical characters.In this paper,a bin category model including detailed microphysical processes has been used to simulate a precipitation of the stratiform cloud on 1 June 2007 in Jilin Province,China.The simulation results depict explicitly both the spectrums of water droplet,ice crystal,graupel,and snow and the vertical distribution of the water content.The comparison between the simulation results and the data observed by Doppler radar and the Particle Measurement System（PMS）indicates that different microphysical processes contribute differently to the forming of particle spectrum within three layers,i.e.ice layer,mixed layer,and warm layer.The results show that the seeding particles from the ice layer to the mixed layer are ice crystals with diameter D300 μm.Seeded from the mixed layer to the warm layer,both melting ice particles and water droplets with D100 μm could collect abundant cloud droplets in the warm layer,leading to an obvious increase of rain intensity in the warm layer.Meanwhile,some rain droplets can be produced by coalescing among small cloud particles in the warm layer.The contribution rates of the three layers to rain intensity are 3.5%、 38.5% and 58% respectively.The rainfall intensity near the ground and the droplet spectrum width are considerably different when there is no mixed layer or warm layer,i.e.,0.475 mm/h and 920 μm for lack of the mixed layer,whereas 0.807 mm/h and 1500 μm without the warm layer.With the absence of ice layer,there is no big difference in both rainfall intensity and water droplet spectrum,and the simulation result is close to that with presence of all the three layers.