Maintenance and development of the Ural high and its contribution to severe cold wave activities in winter 2020/21

2020年底至2021年初,连续两次强寒潮入侵中国东部地区,导致大范围强降温.本文研究这两次寒潮的特征和形成机理.主要结果如下:从2020年12月中旬到2021年1月中旬,乌拉尔山地区维持一宽阔的高压脊.脊前北风的维持和加强导致局地斜压性增加,导致下游横槽槽底等高线梯度加大,冷平流加强,西伯利亚高压加强和向南扩张.准定常波能量传播是乌拉尔山阻塞发展和持续的主要原因.

Two successive severe cold waves invaded eastern China from the end of 2020 to early 2021,leading to an extensive,severe,and persistent drop in temperature.The paper investigates the features and formation mechanisms of the two cold waves.The main results are as follows:(1)An anticlockwise turning of the transverse trough was observed in both cold waves.However,a broad ridge was maintained over the Ural area from mid-December 2020 till mid-January 2021.No breakdown or discontinuous westward shift of the blocking high was observed,which is different from typical cold waves in eastern Asia.(2)The maintenance and strengthening of northerly winds in front of the Ural high led to an increase in baroclinicity in-situ.In the downstream region,the gradient of the geopotential height contour in the south of the transverse trough rapidly increased and the advection of cold temperature consistently enhanced and advanced southwards.This in turn caused the intensification and southward expansion of the Siberian high.(3)Energy propagation of the quasi-stationary wave was a reason for the development and persistence of the Ural blocking.Prior to the occurrence of the two cold waves,the energy of the low-frequency stationary wave originating from near 0°E(or even to the west)propagated eastwards,which helped the Ural ridge intensify and maintain.Meanwhile,it also contributed to the development of the trough downstream of the ridge and resulted in the anticlockwise turning of the transverse trough,providing a favorable condition for the southward outbreak of cold air.