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东亚冬季大范围长时间气温反相事件及成因探究

East Asia large scale temperature reversal events and the exploration of its cause in winter

  • 摘要: 东亚冬季气温存在显著的季节内冷暖起伏,给人民的生产生活带来了深远的影响。本文主要使用1980-2022年冬季逐日NCEP再分析资料,筛选42年冬季中最典型的“冷转暖”事件和“暖转冷”事件,分析了东亚冬季大范围、长时间的气温反相事件的特征及其主要影响因子。结果表明:(1)在42年冬季中存在典型的21个“冷转暖”事件及6个“暖转冷”事件,偏暖和偏冷之间的气温差均高达10℃以上,维持时间超30天,并且“冷转暖”事件和“暖转冷”事件均表现出全区一致的冷暖转相。(2)无论是“冷转暖”事件还是“暖转冷”事件,在温度转相前2天左右乌拉尔山地区的位势高度先发生位相转变。伴随着乌拉尔山地区位势高度异常由负转正,2天后东亚气温将由偏暖转为偏冷,反之亦然。(3)“暖转冷”事件中,乌拉尔山地区位势高度异常的转向与NAO南中心密切相关,在温度转向前35天NAO南中心在平流层已出现位势高度正异常信号,并下传至对流层,形成波作用通量向东传播至乌拉尔山地区,使得其位势高度由负转正,进而造成东亚气温反转。“冷转暖”事件则主要与NAO的北中心有关,温度转向前30天位势高度负异常已出现在平流层,并下传至对流层进一步造成乌拉尔山地区位势高度转向。平流层NAO南、北中心位势高度的变异与相应气温转向事件中气温的30天超前相关系数高达-0.8,因此,对它的监测和预测将有利于我们提前30天预测东亚冬季气温大范围、长时间的季节内转向。

     

    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.

     

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