Effect of the Blocking High-East Asian Trough on Three Extreme Cold Events in Eastern Asia

Three extreme cold events occurred in eastern Asia in January 2016, January 2021, and December 2023. As important factors in atmospheric circulation anomalies, the Blocking High and East Asian Trough (BH-ET) structure played key roles during these three extreme cold wave events. Among these two dynamic patterns, the BH affected the development of the cold waves in two different ways: (1) before the cold waves in 2016 and 2023, the BH pushed the cold air southward, resulting in a slow and gradual cooling, with a cooling rate (CR) in eastern Asia of 1.34 degrees C d-1 and 1.2 degrees C d-1, respectively, and (2) in January 2021, the sudden collapse of BH caused the cold air to rapidly attack mid-latitude regions, with a CR of 1.87 degrees C d-1. In terms of the spatial CR, the temperature drop in 2021 occurred 38.8 % and 55% faster than those in 2016 and 2023, respectively. At the same time, the ET influences the wind direction of cold waves by modulating the pressure gradient. Before the cold waves occurred, the meridional wind field near the ET showed negative values, forming northwesterly or northeasterly winds, which continued to affect the southern part of East Asia. The meridional wind in January 2021 was stronger than those in 2016 and 2023, which is thought to be the reason for the strength of the 2021 cold wave. Finally, results from the temperature Empirical Orthogonal Function (EOF) analysis from 1980-2023 verify an obvious BH-ET structure in the three cold wave events, which suggests that this particular climatological state provides a climatic background for the occurrence of cold waves.

Advances in Atmospheric Sciences