不同边界层参数化方案和陆面过程参数化方案对一次梅雨锋暴雨显式对流模拟的影响分析

ANALYSIS OF THE INFLUENCE OF DIFFERENT PARAMETERIZATION SCHEMES REPRESENTING THE PLANETARY BOUNDARY LAYER AND LAND SURFACE PROCESSES ON CONVECTION-PERMITTING SIMULATIONS OF A HEAVY RAINFALL EVENT ALONG MEI-YU FRONT

利用WRF模式对2007年7月8日淮河地区特大暴雨过程开展显式对流(1.1 km)模拟试验,比较两种边界层参数化方案和三种陆面过程参数化方案对降水模拟的影响。结果表明,不同边界层参数化方案和陆面过程参数化方案主要影响模拟的强降水位置和强度,而对雨带位置的影响不大。采用MYJ边界层方案模拟的强降水更接近观测,采用YSU方案模拟的强降水偏弱;陆面过程参数化方案对比,简单的热扩散方案模拟的强降水最强、最接近观测,而RUC方案模拟的强降水最弱,Noah方案居中;同时改变陆面方案和边界层方案比单一改变其中一种方案对模拟降水的影响更大。造成强降水模拟差异的主要原因是模拟的近地面(约1 km以下)大气的湿度和温度不同,导致支持对流发生发展的入流空气的对流有效位能(CAPE)不同,进而影响模拟的对流强度和地面降水量。对强降水模拟较好的试验模拟的近地面大气湿度更大,环境入流空气的CAPE更大,对流发展更强,地面降水也更强。

Simulation sensitivities of a heavy rainfall event that occurred ahead of a mei-yu front on July 8, 2007 to different parameterization schemes representing the planetary boundary layer （PBL） and land surface processes are analyzed, using six 24-h convection-permitting simulations with the nested grid spacing of 1.11 km. The results show that the different physics schemes mainly affect the location and intensity of heavy precipitation but with little effect on the location and pattern of the accumulative rain belt. The MYJ PBL scheme has better performance than the YSU PBL scheme that produces a smaller amount of precipitation. As for the three land surface parameterization schemes, the simulations utilizing the simple thermal diffusion scheme produce a larger amount of precipitation that agrees best with the observation, followed in turn by the Noah scheme and the RUC scheme. These sensitivities of the precipitation simulation are attributed to the differences of the simulated moisture and temperature profiles in the PBL caused by the different physics schemes, which leads to different convective available potential energy （CAPE） of the environmental inflow air to support the development of the rainy storm. The best-performing simulation produces a moister PBL and larger CAPE and hence stronger con- vective system and more abundant surface precipitation.