AREM3．0模式对“5．31”天气过程的模拟分析

NUMERICAL SIMULATION ANALYSIS OF "5.31" HEAVY RAIN EVENT BY AREM 3.0 MODEL

运用AREM模式对2005年5月31日发生在湖南新邵的一次特大暴雨天气过程进行模拟分析。利用模式输出的1 h基本物理量计算螺旋度,结果表明:螺旋度对特大暴雨的预报有指示意义,特大暴雨产生在低层正螺旋度中心与高层负螺旋度中心相配合的区域。在暴雨强盛期,螺旋度中低层最大正值位于750 hPa,最大负值位于450 hPa。比较新邵1 h实况降雨量和AREM模式模拟的降水值与相应时刻的螺旋度,发现5月31日19～22时之间的暴雨增幅最大,为172 mm/3 h,而螺旋度值也相应出现了最大的增幅20 m2/(s2.3 h),31日21～22时新邵暴雨出现峰值,但螺旋度却开始减小,此后两者又一致地逐渐减弱。

The AREM3.0 model is used to simulate a heavy rainfall on May 31, 2005 in Xinshao, Hunan Province, and the simulation is satisfactory. Based on reliable outputs, the helicity is calculated. It is found that the helicity is an evident predictor of heavy rains. The heavy rain is usually generated where a positive helicity center exists in low-level atmosphere and a negative helicity center in the high level. During the heavy rainfall period, the maximum value of the positive helicity at low levels is found at 750 hPa while the minimum at 450 hPa. Comparing the 1-hr interval observed precipitation with the simulated values, as well as the corresponding helicity, we find that the increment of the rainstorm is the largest during 19：00 - 22：00, May 31, 172 mm/3 h, while the helicity reaches its maximum of 20 m^2/（s^2·3 h）. During the time of 21：00 - 22：00, while the value of the precipitation peaks, the helicity begins to decrease, followed by consistent weakening of them both.