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.