山东初冬一次极端降水和大风天气成因分析

利用常规地面、高空观测、雷达及ERA5再分析等资料,对山东初冬一次极端降水、大风天气成因分析,结果表明：低槽东移发展,冷空气南压,低空切变线配合东北、西北地区地面高压坝形成的“阻挡”形势利于极端降水的产生。本次水汽条件具有较强的极端性,水汽通量辐合远强于气候平均态,925 hPa和700 hPa水汽通量辐合大值区分别与雨、雪区域配合较好。降雨时垂直上升运动中心在边界层,升至600 hPa时转为降雪,降雨时低层辐合、高层辐散,降雪时由低到高呈辐散-辐合-辐散分布。冷锋过境条件对称不稳定触发产生对流,随后在冷锋后侧逆温层上由锋生过程的上升支环流强迫产生高架对流。强冷空气扰动从内蒙古高原下滑至华北平原,与近地面冷平流汇合增强,产生较强变压风,同时促进了势能向动能转换和动量下传。地形强迫造成下沉运动增强,华北地区低层形成锋面次级环流,环流前部锋区暖界面为地转偏差辐合,冷界面为地转偏差辐散。环流内有水平动能和地转偏差大值区,偏北气流和下沉运动使水平动能向南、向下输送,导致地面极端大风。

Cause analysis of one extremely precipitation and gale in Shandong Province in Early winter

Made use of conventional ground and upper air observation data, radar data and ERA5 reanalysis data, the causes of extremely precipitation and gale in early winter in Shandong were analyzed. The results show that: The low trough moved eastward, cold air pressed southward, the "block" situation formed by the cold air pressure from the south and the low altitude shear line in coordination with the high pressure dam in the northeast and northwest of the ground was conducive to the produce of extreme precipitation. The water vapor condition in this process was very extreme, Water vapor flux convergence was much stronger than the climate mean state. The moisture flux convergence regions at 925 hPa and 700 hPa were in good coordination with rain and snow regions respectively. When it rained, the lower layer converged and the upper layer diverged, when it snowed, it presented a divergence - convergence - divergence distribution from low to high. Convection was triggered by asymmetric instability of cold front transit conditions, and then elevated convection was forced by upward-ramus circulation in the inversion layer behind the cold front. Strong cold air disturbance slipped from the Inner Mongolia Plateau to the North China Plain, and convergence with the cold advection intensified, resulted strong barotropic winds, and promoted the conversion of potential energy to kinetic energy and momentum down. Topographic forcing resulted in the enhancement of subsidence movement and the formation of frontal secondary circulation in the lower layer of North China. The warm interface of the front region was the convergence of geostrophic deviation, and the cold interface was divergence of geostrophic deviation. There were large values of horizontal kinetic energy and geostrophic deviation in the circulation, and the northerly airflow and descending movement made the horizontal kinetic energy transport southward and downward, resulted in extreme surface winds.