华北“7.20”特大暴雨多尺度特征分析

利用华北地区248个加密气象观测站资料、FY-2G黑体亮温TBB、邢台站探空资料、华北地区多普勒雷达资料、欧洲中心（ECMWF）0.25°×0.25°和NCEP/NCAR（1°×1°）再分析资料，对2016年7月19—21日一场特大暴雨进行多尺度特征分析。结果表明：200 hPa南亚高压系统呈东西带状分布，500 hPa为“东高西低”环流背景，鄂霍茨克海附近闭合高压下游阻挡效应使上游系统移速缓慢，华北长时间处于深槽之中，环流形势利于产生稳定经向型暴雨；通过高低层流场对比发现，高空急流入口区右侧与低空急流出口区左侧重叠区为最强降水区域，降水大值区均位于太行山及燕山山脉迎风坡；垂直方向上，垂直上升运动中心介于散度辐合中心与辐散中心之间，剧烈的抽吸效应将水汽输送至高层，冷暖气流交汇及水汽上升过程凝结潜热释放导致对流系统迅速发展。河北地区稳定的深厚气旋是本次暴雨的关键系统，19日石家庄地区强对流单体（>45 dBz）存在时间超过20 h。MCS影响范围广、特殊山脉地形作用、系统停留时间较长等原因造成累积降水量增大，是本次暴雨与“7.21”北京特大暴雨相比的突出特点之一。

Multi-scale characteristics of the "7.20" heavy rainstorm event in North China

Multi-scale characteristics of a heavy rainstorm event from July 19 to 21, 2016 were analyzed in this study, using encrypted meteorological observations at 248 stations in North China, the temperature of a black body (TBB) retrieved from the FY-2G satellite, radiosonde data at Xingtai station, Doppler radar data in North China, and the reanalysis data from European Center for Medium-range Weather Forecast (ECMWF) with a 0.25°×0.25° resolution and from the National Centers for Environmental Prediction (NCEP) with a 1°×1° resolution.The results show that the South Asian High at 200 hPa is distributed from east to west, meanwhile, the background atmospheric circulation at 500 hPa is characterized by "east high and west low".Due to the block effect of a closed high pressure near the Sea of Okhotsk, upstream systems move slowly and the area in North China is trapped in a deep trough for a long time period.Such a circulation favors the formation of a stable oriented rainstorm event.In a comparison of flow fields at upper and lower altitudes, the strongest precipitation occurs within the overlying area between the right inlet area of upper-level jet and the left exit area of low-level jet, with the maximum precipitation values occurring at the windward slopes of Taihang Mountains and Yan Mountains.A center of the vertical ascending movements is located between a convergence center and a divergence center.Water vapor is transported to upper levels due to the intense suction effect, and the convective system rapidly develops in the presence of convergence of cold and warm air flows and the release of condensation latent heat during ascending movements of water vapor.A deep and stable cyclone over Hebei province is important for the formation of this heavy rainstorm event, with the lasting time exceeding 20 h of a super convection cell (>45 dBz) in Shijiazhuang on July 19.Cumulative precipitation increases mainly due to a wide effect area of the meso-scale convective system (MCS), the topographic effect of mountains, and long maintaining time of the system, which is also one of the specific characteristics of this heavy rainstorm event in comparison with another heavy rainstorm event in Beijing on July 21, 2012.