层状云结构和降水机制研究及人工增雨问题讨论

Research Progress of Stratiform Cloud Structure and Precipitation Mechanism and Discussion on Artificial Precipitation Problems

总结了层状云及其降水物理研究的部分成果。在此基础上,讨论了层状云人工增雨的几个问题,提出用常规观测资料判断人工增雨条件的方法。具体结果如下:层状云结构是不均匀的。层状云系在垂直方向上具有分层结构。"催化—供给"云是降水性层状云的典型结构,"催化—供给"云相互作用是导致降水的主要过程。按微观结构可以将降水性层状云分成3层:冰相层、冰水混合层和液水层。冰相层是催化云,冰水混合层和液水层是供给云。层状云降水过程研究表明,对应于层状云或"催化—供给"云的3层宏观结构,发生着不同的微物理过程,粒子形成和增长过程也不同。冰相层的冰晶和雪,凝华是其主要增长方式,其次是雪与冰晶的聚合过程;雪(或聚合体)落入冰水混合层后,继续通过凝华增长或贝吉龙过程增长,同时撞冻过冷云水增长,有部分冰雪晶通过撞冻增长而转化成霰。在液水层,雪(或聚合体)霰开始融化,同时收集云暖区云水增长。冰相粒子的撞冻增长过程和凝华增长过程相比同样重要。层状云各层对降水的贡献不同。一般而言,对于"催化—供给"云,催化云对降水的贡献低于30%,供给云在70%以上。在以上研究的基础上,讨论了层状云人工增雨的问题。(1)"催化—供给"云结构有利于云水转化成降水,只有冰相层、冰水混合成和液水层相互"配合",才能形成有效降水。可以将"催化—供给"云作为层状云人工增雨催化的结构条件。(2)要选择降水形成以冷云过程为主的层状云催化,冰面饱和水汽量和过冷水含量要大些。(3)层状云人工增雨原理应该补充。降水形成不但经历贝吉龙-芬德森过程,冰水混合层的聚合和撞冻增长也是十分重要的过程。过冷水对于降水的形成非常重要,但冰面饱和水汽量对降水的形成也同样重要。最后,结合层状云的研究成果,提出用常规探测资料判别层状云人工增雨催化条件的方法:利用卫星云图和雷达回波判别"催化—供给"云的结构,用雷达RHI回波(在距离高度显示器上的回波)判别降水机制和液水层。

Research achievements in cloud and precipitation physics of stratiform clouds are summarized in this paper. Several problems associated with artificial precipitation for stratiform clouds are discussed, and a method of evaluating artificial precipitation conditions by using conventional observation data is offered. Specific results are listed below： The structure of a stratiform cloud is not uniform and includes layered structures in the vertical direction. The＂seeding-feeding＂ cloud is typical structure of stratiform cloud precipitous, and interaction of the seeding cloud and feeding is the main process in precipitation. The stratiform cloud precipitous may be divided into the following three lay- ers according to its microphysical structure： An ice phase layer, a mixed layer with ice and liquid water, and the liquid water layer. The ice phase layer is the seeding cloud, and the mixed and liquid water layers are feeding clouds. A study of stratiform cloud precipitation processes corresponding to the three-layer structure of the cloud revealed differences in microphysical processes, particle formation, and growth processes. Sublimation is the main growth mode of ice and snow crystals in the ice phase layer, followed by the polymerization process of these crystals. Snow, or poly- mers, falling into the mixing layer continue to grow by sublimation or the Bergeron process, in addition to accretion, and some of the ice crystals and snow are converted into graupel. In liquid water, snow, or polymers, begins to melt and to collect cloud water. The accretion and sublimation growth processes are also important for ice particles. Each layer in the cloud provides a different contribution to precipitation. The contribution rate of the seeding cloud is generally less than 30%, and that of the feeding cloud is more than 70%. On the basis of the above study results, the following conclusions are drawn： （1） The seeding-feeding cloud bene- fits from the transformation of cloud water to precipitation, and mutual cooperation among the ice phase, mixing, and liquid water layers results in the formation of effective precipitation. Therefore, the seeding-feeding cloud should act as a seeding condition for artificial precipitation. （2） For a stratiform cloud to be seeded, the cold cloud process is important. For effective precipitation, a super-saturated water vapor amount with respect to ice, in addition to the content of su- per-cooled water, should be high. （3） The artificial precipitation principle for stratiform clouds should be considered. Although the Bergeron-Findeisen process is critical to precipitation formation, aggregation and accretion in the mixing layer, super-cooled water and super-saturated water vapor are also important. Finally, combined with achievements in stratiform cloud research, conventional detection data is used for the dis- criminant method on artificial precipitation conditions of stratiform clouds to determine that the seeding-feeding cloud structure is distinguished by satellite cloud pictures and radar and that the precipitation mechanism and the liquid water layer can be discriminated by using radar range height indicator （RHI） echo.