2017年5月7日广州特大暴雨模拟中的背景场影响分析

2017年5月7日广州发生了特大暴雨,为研究不同背景场资料对这次暴雨过程的影响,模式背景场分别采用美国NCEP的GFS资料和中国的T639资料,利用GRAPES_Meso模式对这次暴雨过程进行了数值模拟和影响分析;数值试验结果表明,采用不同的背景场对这次暴雨过程具有显著影响,用T639资料(T639_run)作为模式背景场大致模拟出了这次暴雨过程,而采用NCEP GFS数据(GFS_run)模拟的降水明显偏北。其原因是,采用T639资料做背景场时,华南暴雨区域存在深厚的水汽输送,同时存在强烈的上升运动,可以产生极端强降水;而采用GFS资料进行数值模拟时,实际暴雨区上空的上升气流较弱,水汽输送也较弱,使强降水落区偏北。GRAPES_Meso模式模拟的华南地区的云顶高度整体偏高,云顶温度整体偏低,相对来说,采用T639_run的模拟结果优于GFSrun的结果,该研究结果可以为云降水方案中的水物质和云量计算方案的改进和优化提供一定的参考。

Impact of Background Field in the Numerical Simulation of Extremely Severe Rainstorm in Guangzhou on 7 May 2017

A torrential rainfall event occurred in Guangzhou on 7 May 2017. In order to study the impact of different background field data on the simulation of rainstorm process, the NCEP Global Forecast System (GFS) data and CMA T639 data were used separately to develop lateral boundary and initial conditions for the numerical simulation and impact analysis of the rainstorm with the GRAPES_Meso model. The results indicated that background fields have significant impact on the simulation of rainstorm process. The precipitation forecasts using T639 data (T639_run) as initial and boundary conditions seem to be roughly simu lated, while the location of the rainfall simulated by GFS data (GFS_run) is obviously northerly. The reason is that there is a deep water vapor transport and strong ascending motion in the rainstorm area of South China using T639 data as the background field, which can produce extremely heavy rainfall. The updraft and water vapor transport are weak in the actual storm area simulated by GFS data, making the heavy precipitation area northerly. Overall, the height of cloud top is higher and the temperature of cloud top is lower simulated by GRAPES_Meso model. Relatively speaking, the simulation result using T639_run is better than using GFS_run. This research result could provide a reference for the improvement and optimization of the calculation about the water substances and cloud fraction in cloud schemes.