浙江一次江淮气旋后部强对流暴雨过程诊断研究

DIAGNOSTIC RESEARCH OF SEVERE CONVECTIVE RAINSTORM EVENT AT THE BACK OF A JIANG-HUAI CYCLONE IN ZHEJIANG PROVINCE

关键词:  强对流暴雨  冷式切变  垂直螺旋度  湿位涡  积雨云

Key words:  severe convective rainstorm  cold shear  vertical helicity  moist potential vorticity  cumulonimbus cloud

摘要:

利用地面降水观测、NCEP/NCAR FNL再分析、ECMWF模式预报场和FY-2H静止卫星TBB资料，对2020年6月30日浙江省一次暴雨过程进行了综合分析。结果表明：(1) 200 hPa南亚高压强高空辐散、中纬度低槽东移、副热带高压带状稳定的阻塞形势、江淮气旋后部下摆冷空气与暖湿气流交汇形成的冷式切变等共同提供了有利的环境条件；(2) 对流层中低层水汽通量向高空伸展、700 hPa正的垂直螺旋度中心都对暴雨落区有示踪作用，高层正水汽通量散度强于低层负水汽通量散度，垂直螺旋度和垂直速度中心几乎重合，先低层强辐合后强垂直上升运动均为本次暴雨的发生提供了重要的水汽和动力条件；(3) 暴雨发生在MPV、MPV1和MPV2为正负过渡的零值区，为对流不稳定和斜压不稳定相结合区域，θse线密集区与地面近乎垂直，湿位涡的高值中心位于θse梯度最大处，高空湿位涡下传触发了位势不稳定能量的释放，引起大范围的强对流暴雨；(4) 850 hPa冷切变线附近的降水云团，是由多个块状对流云团合并加强形成完整的带状积雨云团，而上游不断有新生对流云团生成东移补充消散的老单体，触发阶段对流云后向传播，扰动发展阶段对流云团合并过程，形成对流云串的“列车效应”。

Abstract:

Based on surface precipitation observational data, NCEP/NCAR FNL reanalysis data, ECMWF model prediction field data and FY-2H geostationary satellite TBB data, the present study analyzed a rainstorm process in Zhejiang Province on June 30, 2020. The results show that: (1) Favorable conditions for the process include the strong upper-air divergence of the 200 hPa South Asian High, the eastward movement of the low trough in the middle latitudes, the stable blocking of the subtropical high, and the cold shear formed by the intersection of the cold air and the warm and wet air at the back of the Changjiang River-Huaihe River Cyclones (Jianghuai Cyclones). (2) The expansion area of water vapor flux in the mid-low troposphere and the vertical helicity at 700 hPa are both good indicators for heavy rain. The positive water vapor flux divergence at the upper troposphere is stronger than the negative one at the lower troposphere. The vertical helicity and the vertical velocity center almost coincide. The strong low-level convergence followed by the strong vertical upward movement provide good water vapor and dynamic conditions for the rainstorm. (3) The rainstorm area is located near the transition zone of the positive and negative value of MPV, MPV1 and MPV2. This zone is also the conjoint area of convective and baroclinic instability. The region in which the isentropic of θse densely distributed is almost perpendicular to the ground. The high-altitude cold air flow drives the high-potential vortex to the lower level, causing regional severe convective rainstorm. (4) The precipitating cloud near the cold shear line at 850 hPa has been consolidated from multiple massive convective clouds into a completely banded cumulonimbus cloud, and newborn convective clouds move eastward continually from the upstream, forming a significant “train effect”.