不同云方案对祁连山降水模拟的影响

应用MM5中尺度模式,选用4种不同云微物理方案(Dudhia简单冰相方案、Reisner混合相方案、Reisner2霰方案和Schultz微物理方案),对2002年7月12-13日祁连山区降水过程进行了数值模拟试验。模拟结果的对比分析表明,不同云微物理方案在祁连山区降水的模拟中对降水落区的模拟均偏南;除Reisner2霰方案外,其他3种方案对降水中心落点的模拟影响不大,降水中心强度对云微物理方案不敏感;显式降水和参数化降水对云微物理方案有不同程度的依赖性;云微物理过程通过影响动力条件发生发展的时间和强度,来影响强降水发生的时间和强度。通过各云微物理参数的分析发现,各物理过程中微物理参数参与降水的过程不同:对Dudhia简单冰相方案来说,雨水和云水是形成降水的主要过程;Reisner混合相方案中降水的形成主要是由于雨水、云水、雪和霰的碰并过程,冰晶的碰并相对较弱;在Reisner2霰方案中,雨水、云水、冰晶、雪和霰均参与碰并碰冻过程;Schultz微物理方案中冰晶、雪和霰的碰并过程更为重要。

Cloud microphysical processes on simulation of precipitation in Qilian Mountains

Based on the MM5 model with four different cloud microphysical schemes(Duhia simple ice,Reisner mix phase,Reisner2 graupel and Schultz microphysical schemes),numerical simulations are carried out to study the cloud physical processes in a rainfall event over Qilian Mountains during 12-13 July 2002.Comparisons among the experiments and against the observations indicate that the simulated rainfall area from the four cloud physical processes are further south than the observed one.Except Reisner2 graupel scheme,other three schemes have little effect on the center of rainfall area,and the intensity of precipitation center is not sensitive to cloud microphysical processes.The explicit precipitation and parameterize precipitation depend on different cloud microphysical processes.Cloud microphysical processes impact on the occurrence time and intensity of strong precipitation by affecting the occurrence/development times and intensity of dynamic conditions.Analysis of the cloud microphysical parameters shows that the processes of the parameters concerned with precipitation are different for the four different schemes.For Duhia simple ice scheme,rain water and cloud water are primary.For Reisner mix phase scheme,the collection of rain water,cloud water,snow and graupel may paly a main role for precipitation,and the coagulation of ice crystal is relatively weak.For Reisner2 graupel scheme,rain water,cloud water,snow,ice and graupel all are concerned with collection and accretion processes.For Schultz microphysical scheme,the collection of ice,snow and graupel is more significant.