Abstract:
Winter temperatures in East Asia have significant subseasonal oscillation, which have a profound impact on people"s production and life. Based on the reanalysis data of NCEP during the period of 1980–2022, the most typical temperature reversal events in winter of 42 years were found and analyzed in terms of their characteristics and main influencing factors by using correlation analysis, power spectrum analysis, butterworth filter, Plumb wave activity flux analysis and other statistical methods. The results show that: (1) In the winter of 42 years, there are 21 typical "cold-to-warm" events (CTWE) and 6 "warm-to-cold" events (WTCE). In all events, the temperature difference between the warm and cold period was more than 10℃. Besides, the temperature reversal was observed over the whole region. (2) In all events, the geopotential height anomaly in 500hPa over the Ural Mountains has a phase transition 2 days before the reversal of the East Asian temperature. During the WTCE, the anomalous geopotential height of the Ural Mountains changes from negative to positive, 2 days later the temperature anomaly in East Asia changes from warm to cold, and vice versa. (3) Further analysis reveals that during the WTCE, the reversal of the anomalous geopotential height in the Ural Mountains region is closely related to the southern center of NAO. 35 days before the reversal of East Asia temperature, positive geopotential height anomaly has been observed in the southern center of NAO in the stratosphere, then it propagates downward to the troposphere and excites wave flux propagating eastward to the Ural Mountains region, further leading to the anomalous geopotential height in Ural Mountains transition from negative to positive. However, the CTWE is mainly related to the northern center of NAO. Negative geopotential height has existed in the norther center of NAO in the stratosphere 30 days before the reversal of East Asian temperature anomaly. The 30-day leading correlation coefficient between the geopotential height of NAO centers and the corresponding temperature anomaly in different reversal events is as high as -0.8, exceeding 95% confidence level. Therefore, monitoring and prediction of the geopotential height over NAO centers in stratosphere will help us to predict the subseasonal reversal of winter temperature in East Asia 30 days in advance.