East Asia Large-Scale Temperature Reversal Events in Winter and the Exploration of Their Cause

Winter temperatures in East Asia exhibit significant subseasonal oscillations, profoundly affecting production and daily life. Using NCEP-NCAR reanalysis data from 1980 to 2022, the most typical winter temperature reversal events over the past 42 years were identified and analyzed. This analysis focused on their characteristics and main influencing factors, employing correlation analysis, power spectrum analysis, Butterworth filter, Plumb wave activity flux analysis, and other statistical methods. Key results include: (1) The analysis of 42 winters identified 21 typical “cold-to-warm” events (CTWEs) and 6 “warm-to-cold” events (WTCEs). In all events, the temperature difference between the warm and cold periods exceeded 10°C. Temperature reversals were observed over the whole region. (2) In all events, a phase transition in the 500-hPa geopotential height anomaly over the Ural Mountains occurred 2 days before the East Asian temperature reversal. During WTCEs, this anomaly shifted from negative to positive, leading to a warm-to-cold temperature change in East Asia after two days and vice versa. (3) Further analysis reveals that WTCE reversals are closely related to the southern center of the North Atlantic oscillation (NAO). Thirty-five days before the temperature reversal in East Asia, a positive geopotential height anomaly was observed in the southern center of NAO in the stratosphere. This anomaly propagated downward to the troposphere, exciting a wave flux that moved eastward toward the Ural Mountains region, leading to a transition of the geopotential height anomaly from negative to positive in that region. However, the CTWEs were mainly affected by the northern center of NAO, where a negative geopotential height anomaly was present in the northern center of NAO in the stratosphere 30 days before the East Asian temperature anomaly reversal. The 30-day leading correlation coefficient between the geopotential height changes in the NAO centers and the corresponding temperature anomalies in different reversal events is as high as −0.8, exceeding the 95% confidence level. Therefore, by monitoring the geopotential heights in the southern and northern NAO centers in the stratosphere, we can predict East Asian winter temperature reversals up to 30 days in advance.