一次暴雨过程的锋生特征及风场演变分析

Analysis of frontogenesis characteristics and the winds field evolution of a rainstorm process

本文利用ECMWF ERA-INTERIM(0.25°×0.25°)再分析资料和FY-2H卫星云顶亮温资料,通过计算锋生函数、非地转风、水平风切变强度的分布与暴雨的关系,对2020年7月5—7日江苏一次暴雨过程的成因进行了诊断分析。结果表明,强降水区中低层锋生、中高层锋消。850 hPa锋生变化能反映出对暴雨的影响,散度项、变形项对锋生为正贡献,变形项、倾斜项与总锋生变化趋势基本一致,散度锋生始终伴随整个降水过程,暴雨最强阶段是由倾斜锋生叠加在水平锋生上作用的结果。锋生加强了风场的非地转性,并强迫出锋面次级环流,非地转风的散度形成次级环流上升支。对流层低层,锋生强度随急流发展同步增强。200 hPa高空急流经向v场变化与暴雨强度演变趋势正相关:暴雨开始阶段,v场增大,降水增强;当高空急流v场最大时,暴雨最强;暴雨减弱结束阶段,高、低空v场减小,北风增大,高空西南风急流右后方次地转现象消失,转为超地转西南风。

By using ECMWF ERA-INTERIM(0.25°×0.25°)reanalysis data and FY-2H TBB data,through calculating the relationship between frontogenesis function,non-geostrophic wind,horizontal wind shear intensity distribution and rainstorm,the cause of a rainstorm process in Jiangsu on July 5-7,2020 was diagnosically analyzed.Results indicate that in areas of heavy precipitation,frontogenesis occurs in the middle and lower layers,and frontogenesis disappears in the middle and upper layers.The 850 hPa frontogenesis change can better reflect the impact on rainstorm.Divergence term and deformation term are positive contributions to frontogenesis.The deformation term and tilt term are basically consistent with the change trend of total frontogenesis.Divergence frontogenesis is always accompanied by the whole precipitation process.The strongest stage of rainstorm is the result of superposition of tilt frontogenesis on horizontal frontogenesis.Frontogenesis strengthens the non-geostrophic nature of the wind field and forces secondary circulation on the front,with the divergence of non-geostrophic winds forming an ascending branch of the secondary circulation.In the lower troposphere,the intensity of frontogenesis increases synchronously with the development of the jet stream.The meridional v field change of 200 hPa upper air jet is positively correlated with the evolution trend of rainstorm intensity:at the beginning of rainstorm,v field increases and precipitation increases;when the upper jet v field is the largest,the rainstorm is the strongest;at the end of rainstorm weakening,the high and low level v fields decrease,the north wind increases,and the secondary geostrophic phenomenon in the right rear of the upper level southwest jet disappears,turning into the super geostrophic southwest wind.