【摘要】 针对2015年8月3日发生在西安地区的一次强降水,首先利用WRF-3DVAR同化系统循环同化雷达反射率和径向风资料来减小模式初始场误差,以此增加基于模式预报结果分析研究的可信度,然后采用敏感试验手段探究有无城市下垫面对西安地区强对流性天气的影响。结果表明,同化雷达资料可以改善降水预报,其中10～25 mm降水TS (True Shooting)和ETS (Effective True Shooting)评分较未同化结果分别提高0. 188和0. 187,降水落区和强度与观测接近。有无城市下垫面的对比试验发现,有城市时,城区平均对流有效位能增大而对流抑制能减小,低层风速减小,城区上空假相当位温的垂直梯度变大,大气更加不稳定。城市下垫面使城区降水增强,若用农田代替城市下垫面会使降水落区向南漂移约0. 2个纬距。更多还原

【Abstract】 On August 3,2015,a heavy rainfall occurred in Xi’an with floods and heavy losses. To better investigate the rainfall,highly temporal and spatial resolution radar data,mesoscale WRF model and its 3 DVAR assimilation system were used. After assimilating the radar data,the precipitation area and intensity were improved,and the TS( True Shooting) and ETS( Effective True Shooting) scores of 10～25 mm precipitation increased respectively by 0. 188 and 0. 187 compared with no data assimilation. Then two experiments with and without urban surface( CITY and NoCITY) were carried out to explore the impact of urban surface on forecast of precipitation.In CITY,the average convective available potential energy( CAPE) increased and the convective inhibition energy( CIN) reduced,low-level wind speed became smaller,and vertical gradient of the pseudo-specific temperature was larger and the atmospheric became more unstable than those in NoCITY. The urban surface enhanced precipitation over the urban area; if the urban surface was substituted by a cultivated land,the precipitation area would shift southward approximately. 2 latitudes.更多还原