Maintenance and Development of Ural Blocking High and its Relationship with Severe Cold Wave Activities in 2020/2021 Winter

Between late 2020 and early 2021, eastern China was struck by two consecutive cold waves, leading to an extensive, severe, and persistent drop in temperature. This paper explores the features and formation mechanisms of the circulation related to these two cold waves. The primary results are as follows: (1) The circulation patterns of these two cold waves are recognized as a type of “anticlockwise turning of the transverse trough.” However, a broad ridge (or blocking high) was maintained over the Ural region from mid-December 2020 to the end of the second cold wave. The blocking high did not experience a breakdown or “discontinuous westward shift”, which differentiates it from the common cold waves in eastern Asia. (2) The maintenance and strengthening of northerly winds downstream of the Ural high results in an increase in the baroclinicity in situ. In the region downstream of the Ural high, the gradient of the geopotential height contour in the south of the transverse trough rapidly increases, and the cold temperature advection consistently enhanced and southward advanced. The aforementioned phenomena cause the intensification and southward expansion of the Siberian High. (3) Before the occurrence of the two cold waves, the energy of a low-frequency stationary wave originating at 0°E (or the west) propagates eastward, which favors the maintenance and intensification of the Ural ridge and the development of the trough downstream, offering a favorable condition for the southward outbreak of cold air.