2022年北京延庆一次暴雨空报过程的中尺度特征分析

Analysis of a Falsely Predicted Rainstorm Mesoscale Characteristics in Yanqing, Beijing in 2022

利用常规气象观测数据、风廓线雷达、雷达变分同化分析系统(VDRAS)风场、北京雷达拼图以及欧洲中心EC数值模式和欧洲中心ERA5大气再分析资料(0.25˚ × 0.25˚),对2022年7月5日延庆暴雨空报过程的中尺度特征和预报偏差进行分析,结果表明:1) 延庆此次降雨过程主要系统是西来槽与低层切变线,本区具备出现暴雨的环境条件,但需要明显触发抬升条件。2) 延庆站风廓线14:00至17:20期间呈现风随高度顺时针旋转变为逆时针旋转的特征,大气状态逐渐趋于稳定,并观测到16:54至17:24期间海拔2000米上下出现了反气旋环流,对应17时纬向垂直环流场在延庆中南部(116.25˚E)上空存在明显下沉运动,其抑制了延庆中南部对流发展加强。3) 预报失误的主要原因是着重考虑了低涡外围偏东风对延庆的影响,未考虑14~15时延庆西北部分散对流回波其冷出流已使延庆大气层结条件趋于稳定这一因素,同时在这次需要触发机制的降雨过程中,八达岭地形可能起到了一定的阻挡作用。Using conventional meteorological observation data, wind profile radar, the Variational Doppler Radar Analysis System (VDRAS) wind field, the Beijing radar mosaic, as well as numerical models from the European Centre for Medium-Range Weather Forecasts (ECMWF) and the ERA5 atmospheric reanalysis data (0.25° × 0.25°), an analysis of the mesoscale characteristics and forecast deviations of a falsely predicted rainstorm event in Yanqing, China on July 5 2022, , was conducted. The results indicate the following: 1) The evolution of the event was fundamentally steered by a westward-propagating upper-level trough and a low-level shear line, which, though conducive to rainstorm development, lacked an overt triggering mechanism. 2) Vertical wind shear profiles obtained from wind profiler radar indicate a transition from cyclonic to anti-cyclonic rotation with height, indicative of atmospheric stabilization processes. Notably, an anti-cyclonic circulation centered at approximately 2000 meters above ground level corresponded to subsidence over central-southern Yanqing, which acted to suppress convective activity. 3) The forecast deviation is attributed to an overestimation of the influence of easterly winds surrounding the vortex on Yanqing, and ignoring the scattered convective echoes in the northwest part of Yanqing between 14 and 15 o'clock, its cold outflow tends to stabilize the atmospheric stratification conditions in Yanqing. At the same time, as a triggering mechanism is required for this rainfall, the terrain of Badaling may serve as a barrier to some extent.