Analysis of Extreme Cold Event in 19-24 February 2022 in Yunan Province
Affected by the strong cold air in 19-24 February 2022, an extreme cold event occurred in Yunnan, which was characterized by sharp drop in temperature， affecting large areas and lasting a long time. In this paper, the extreme characteristics of the cold event and the evolution characteristics of the upper and lower atmospheric circulation during the process are analyzed by using the data of 124 meteorological observation stations in Yunnan, the reanalysis data of NCEP/NCAR and ERA5 atmospheric circulation. The results show that this cold event was very extreme, and was the second strongest cold wave weather event in Yunnan in recent ten years. The cold air intensity at 69 stations reached the cold wave standard, of which the daily average temperature at 10 stations reached or broke the lowest temperature record in February. During the cold event, the rainy and snowy weather was prominent, the accumulated precipitation in the process was close to the climatological precipitation in February, and the scope of a single day snowfall was the largest in recent 20 years. The factors that affected the strong cold event were extremely complex. The cold air activity was closely related to the strengthening and evolution of the atmosphere circulation system in midhigh latitudes, such as the Ural high ridge, the East Asia trough, the Asian upperair westerly jet, the Siberian high, and was also associated with the eastward propagation of the subtropical abnormal Rossby wave train which was originated from the North Atlantic Region. This abnormal Rossby wave train played an important role in guiding the southward dispersion of wave energy and the southward movement of cold air in the Tibetan Plateau, and had a certain impact on the strengthening of southwest water vapor transport in front of the south branch trough. Meanwhile, the convective activities in the tropics also had a certain impact on the strengthening of cold air in East Asia. During the cold event, the cold air flew southward along the northeast path, influencing Yunnan. The intersection of cold and warm air in Yunnan was very prominent, resulting in significant cooling, rain and snow during the cold event.