福建一次大暴雨过程的多尺度分析

Analysis of Multi-Scale Characteristics of a Severe Rainstorm in Fujian

利用常规气象资料、自动气象站降水资料和NCEP再分析1°×1°等资料,对福建2017年6月初一次强降水过程进行多尺度分析。结果表明:(1)冷空气与暖湿气流相互作用形成持续性暴雨,中尺度系统的活动导致短时暴雨。(2)较大的风暴相对螺旋度,低层的正涡度和中低层的上升运动有利于中尺度对流系统(MCS)的发展和维持;强烈的热力不稳定和较强的垂直风切变是中尺度对流发展的环境特征。(3)强的整层水汽通量和水汽辐合为暴雨区提供水汽来源和水汽条件。(4)锋生的大小和位置对降水的强度和落区有很好的指示作用;低层以水平锋生为主,中层以垂直锋生为主,有利于成片暴雨的发生。(5)中尺度系统对天气尺度的水汽辐合和边界层对流不稳定条件有增幅作用;上下两支次级环流的上升支叠加,有利于低层不稳定能量的释放,促进中尺度系统的发展。

By utilizing the conventional meteorological data,precipitation data of automatic meteorological stations,and NCEP reanalysis data(1°×1°),the process of the severe rainstorm happened in Fujian in early June 2017 is analyzed.Some conclusions are derived from the results:(1)The continuous precipitation was formed by the interaction of the northern cold air flow and the warm and wet flow from the south.The activity of mesoscale systems caused the short-term rainstorm.(2)Relatively large relative helicity,positive vorticity at the lower level,and rising movement at the middle and low levels were beneficial to the development and maintenance of MCSs.Strong thermal instability and strong vertical wind shear were the ambient characteristics of mesoscale convective development.(3)The strong whole layer vapor flux and water vapor convergence provided water vapor sources and conditions for the rainstorm area.(4)The size and position of the frontogenesis can be exploited as good indicators of the intensity and the falling area of the rainstorm.The lower level was dominated by horizontal frontogenesis and the middle-level was dominated by vertical frontogenesis,which was beneficial to large areas of heavy rainfall.(5)The mesoscale systems played a role in strengthening synoptic scale water vapor convergence,and meanwhile enhanced the convective instability conditions of the boundary layer.The upper and lower branches of the two secondary circulations were superposed,and this superposition was beneficial to the release of the instability energy accumulated at lower level,and promoted the development of the mesoscale system.