Abstract:
Based on surface and sounding data, radar data and ECMWF (ERA5) 0.25°×0.25° global reanalysis data, the circulation situation, environmental conditions, radar products and the evolution characteristics of headwind area during a local heavy rainstorm were analyzed, which happened in Jiaozhou Bay, Qingdao City on August 19, 2016. The results show that surface cold front at the edge of the subtropical high entering the inverted trough, and the convective weather triggered by the infiltration of cold air into the warm area of the surface convergence line was the formation mechanism of this process. The heavy rainstorm process was closely related to the topography, and it mainly distributed in the large value area of the front vortex of the windward slope formed by the low altitude warm and humid air flow and mountain uplift, and the vertical ascending motion in the middle and low levels and relative humidity in this area are well coordinated. The period of heavy precipitation in the heavy rainstorm area was consistent with the period of vertical ascending motion, and the maximum hourly rainfall appeared in the jump stage of vertical ascending motion intensity. The height of 0℃ layer and the specific humidity of the near surface layer had little change before the beginning of precipitation, while the instability indexes of CAPE, K index and vertical wind shear were significantly enhanced compared with 8.a.m. The analysis of radar products showed that the convective cells causing the heavy rainfall were convective storms in the warm zone, and the vertical wind shear increased 20~30 minutes before the heavy rainfall. The four headwind areas generated during the precipitation process all appeared after the formation of the convective cells, which were the divergent airflow generated by the downdraft of the convective cells in the opposite direction to the ambient wind. Among them, the upwind area of the two low-level relative humidity areas with large value can be developed and enhanced, while the development of the upwind area further promoted the enhancement of convection. This evolution feature has a good indicator function for the near forecast and early warning of the heavy rain process.