2021年中国降水异常气候特征及4次典型极端天气过程分析

Analysis of unusual climatic characteristics of precipitation and four typical extreme weather processes in China in 2021

2021年,我国天气形势复杂,气候异常性显著,极端事件频发。本文简要回顾了我国主汛期和华西秋雨的异常性特征,并对河南和湖北4次高影响天气过程展开了初步分析。结果表明:(1) 2021年4-10月全国平均降水较常年同期偏多7.8%,其中河南、河北和山西等部分地区偏多1倍以上。(2)在外强迫因子“拉尼娜”异常海温的影响下,副热带高压外围水汽和北方冷空气异常活跃,导致华西秋雨降水量打破1961年以来历史记录。(3)河南“21.7”特大暴雨发生在台风、低涡、切变线和辐合线共同作用的背景下,大量来自西北太平洋的水汽,在低空急流与边界层急流耦合、地形的动力阻挡抬升和热力抬升共同作用下,强降水雨带出现在山前。(4)在有利的多尺度环流背景下,地形与低层风场辐合带的相互作用触发了对流,并使得降水维持在狭长山谷地形区域内,引发随州“8.12”极端强降水。(5)中γ尺度的强对流单体的合并加强导致了武汉两次对流大风事件,中层突然增强的水平风引发了下沉运动,下落后造成地面局地强冷池和地面极值大风。

In 2021, the weather situations are complex, the climate anomaly is significant, and extreme events occur frequently in China.This paper briefly reviews the abnormal characteristics of the main flood season over China and Huaxi Autumn Rain, and makes a preliminary analysis of four high impact weather processes in Henan and Hubei. The results show that the mean precipitation over China from April to October 2021 was 7.8% more than its normal value, specifically 100% more than that in some areas such as Henan, Hebei and Shanxi Province. Under the influence of the external forcing factor "La Nina" abnormal SST, the water vapor in the periphery of the subtropical high and the cold air in the north were very active, the Huaxi Autumn Rain broke the historical record since 1961. The "21.7" rainstorm in Henan Province occurred under the background of typhoon, vortex, shear line and convergence line. A large amount of water vapor from the Northwest Pacific appeared in front of the mountain under the coupling of low-level jet and boundary layer jet, dynamic blocking uplift and thermal uplift of terrain. Under the favorable multi-scale circulation background, the interaction between the terrain and the convergence zone of low-level wind field triggered convection, maintained the precipitation in the narrow and long valley terrain, and triggered the "8.12" heavy precipitation in Suizhou Hubei Province. The merging and strengthening of meso-γ scale strong convective cells caused two convective gale events in Wuhan. The sudden enhanced horizontal wind in the middle layer triggered the sinking movement, and the falling created the local strong cold pool and the extreme gale on the ground.