亚欧中纬度关键区正位势高度距平场配置与中国冬季区域性极端低温事件的联系

基于中国地面台站观测资料和NCEP再分析资料,研究了欧亚中纬度500 hPa高度场关键区正异常配置及其与中国冬季区域性极端低温事件(Regional Extreme Low Temperature Events, RELTE)的联系。结果表明,发生RELTE时乌拉尔山(简称乌山)、贝加尔湖(简称贝湖)和雅库茨克—鄂科斯克海(简称雅鄂)附近的某一区域出现高度场正异常的概率为0.83,即欧亚关键区500 hPa正高度距平场的相互匹配是形成RELTE的直接原因。在此基础上,将三个关键区域高度场异常配置分为7种类型:乌山型、贝湖型、雅鄂型、乌山—贝湖型、乌山—贝湖—雅鄂型、乌山—雅鄂型、贝湖—雅鄂型。不同类型异常模态对应的RELTE在空间分布、持续时间和强度等各有差异,如:乌山型对应RELTE以全国型为主,平均持续天数达14.2天;乌山—雅鄂型对应的RELTE以东北—华北型为主,事件平均持续天数为14.1天。此外,不同类型的异常配置均对应有超前于RELTE的前期特征,平均超前时间为1~8天不等。超前天数的空间分布、高度场异常的时间演化,进一步揭示了乌山以西和雅鄂以东两个方向高度场异常的发展并形成多种环流异常模态的过程,也验证了RELTE存在前期信号的可能性。

The Euro-Asia Height Positive Anomalies Character and Its Probable Influence on Regional Extreme Low-Temperature Events in Winter in China

Based on observation data and NCEP/NCAR reanalysis data, the 500-hPa height positive anomalies mode of Euro-Asia and its probable influence on regional extreme low-temperature events (RELTEs) in China during winter are investigated. The results indicate that the probability of positive anomalies occurring in one of three areas (Ural, Baikal, or Okhotsk) is 0.83 when there is a RELTE, suggesting that the height anomalies mode in high areas of the Euro-Asia blocking might be directly responsible for such RELTEs. The modes with positive height anomalies are divided into 7 types, with positive anomalies in Ural, Baikal, Okhotsk, Ural-Baikal, Ural-Baikal-Okhotsk, Ural-Okhotsk, and Baikal-Okhotsk. Each RELTE corresponds to a different anomaly mode, with differences in spatial distribution, duration, and intensity. For example, the positive anomalies modes of Ural-Baikal and Ural-Okhotsk always correspond to RELTEs affecting all of China and northeast-northern China, with average durations of 14.2 and 14.1 days, respectively. Furthermore, each type of positive height anomaly provides advance warning of the RELTEs, with average lead times of up to 1-8 days. The spatial distribution of average advance days and the development of height before or after the first day of RELTEs also suggest that the positive height anomalies mode could develop from two directions: west of Ural or east of Okhotsk. This further validates the probability of the advance warning for RETLEs.