The impact of two atmospheric circulation patterns in Asia on low-temperature events in Yunnan province during winter

Using the daily average temperature data of 125 national meteorological observation stations and NCAR/NCEP reanalysis data from 1961 to 2022, the main patterns of Asian circulation changes in winter and their impact on low-temperature events in Yunnan province were analyzed. The results show that there are two patterns of atmospheric circulation at 500 hPa in Asia during winter, namely zonal and meridional patterns, and the impact of the two patterns on low-temperature events in Yunnan province is significantly different. During the zonal circulation pattern, the stronger cold air flows directly southward from Lake Baikal to low latitudes, mainly affecting the eastern part of East Asia. The low-temperature events in Yunnan province also mainly occur in the eastern region. At this time, the low-temperature process is closely related to the strengthening of the Ural Mountains High and the Siberian High, as well as the wave trains at mid-to-high latitudes in Eurasia. During the meridional circulation pattern, the cold air flows southward along the eastern coast of the East Asian continent with the northerly airflow of the eastern side of the anomalous anticyclone in Lake Baikal, and moves southeast in the form of backflow in mid-to-low latitude areas. The activity is located southward and westward, which is beneficial for the low temperature of Yunnan province, the Tibet Plateau, and low latitude areas in Southeast Asia. At this time, the low-temperature events are mainly related to the changes in the subtropical wave train and the strengthening of positive surface level pressure (SLP) anomalies on the Tibet Plateau, but not closely related to the strengthening of High pressure in the Ural Mountain and the Siberian.