Abstract:

Based on GSI (Gridpoint Statistical Interpolation) assimilation system, the processes of rainstorm occurring in southwestern Hu’nan from 5 to 7 April 2014 were simulated by the Ctrl (no assimilating radiance) and Expl (assimilated the radiance from AMSU-A satellite into initial field of the weather research and forecasting (WRF) model) experiments, and the simulated results in two groups experiment were compared with the observation. Result are as follows: (1) The assimilation of AMSU-A radiance was efficient to reduce rainstorm false rate of forecast, and the accuracies of the simulated range and intensity in precipitation center were significantly improved. The assimilating radiance had a great contribution to adjust the initial field. The disparities of wind field and vorticity field mainly reflected on the weakening of dynamic mechanism, while the relative humidity field presented on the decrease of the water vapor transportation in precipitation center of southwestern Hu’nan and northeastern Guangxi, thus reduced the false center of rainfall in northeastern Guangxi. (3) After assimilating radiance data, the ascending motion between 108°E and 108.7°E along rainstorm center strengthened, and the humidity in high level increased, which consisted with the increase of precipitation in Guizhou. Meanwhile, the ascending motion over the rainstorm center reduced, and the relative humidity in high and low layer decreased, which caused the decreasing of precipitation, thus the simulated results after the simulation was closer to the observation.

Key words: GSI, AMSU-A radiance data, numerical simulation, rainstorm

摘要：

基于GSI(Gridpoint Statistical Interpolation)同化系统，将AMSU-A辐射率资料同化进初始场，针对2014年4月5～7日发生在我国湘西南地区的一次暴雨过程进行模拟研究，并对比了AMSU-A辐射率资料同化前后2组试验方案的模拟结果。发现：（1）同化AMSU-A辐射率资料后有效地减小了对此次暴雨的空报率，且对降水中心的范围和强度模拟的准确性均显著提高；（2）辐射率资料的同化对初始场的调整有较大贡献。其中，风场和涡度的差异主要体现在动力机制的削弱，而湿度场的差异体现在对降水中心水汽输送的减弱，从而减少了虚假的降水中心；（3）同化辐射率资料后，沿暴雨中心108°E~108.7°E范围的上升运动得到加强，且高层湿度增加，与贵州境内降水量增加相符。同时，暴雨中心附近上空上升运动减弱，高低层相对湿度均减小，造成其降水量减小，模拟结果更为接近实况。

关键词: GSI, AMSU-A辐射率资料, 数值模拟, 暴雨