Definition of Early and Late Winter and Associated Interannual Variations of Surface Air Temperature in China
Received:October 09, 2018  
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KeyWord:Early winter  Late winter  In-phase evolution  Out-of-phase evolution  Stationary waves  Transient waves
Author NameAffiliationE-mail
WEI Wei Chengdu Meteorological Bureau, Chengdu 611130  
WANG Lin Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029 wanglin@mail.iap.ac.cn 
CHEN Quanliang Plateau Atmosphere and Environment Key Laboratory of Sichuan Province/School of Atmospheric Sciences, Chengdu University of Information Technology, Chengdu 610225  
LIU Yuyun Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029  
LI Zhen Key Laboratory of Regional Climate-Environment in Temperate East Asia, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029  
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Abstract:
      Based on daily mean air temperature (T m) and daily minimum air temperature (T min) data from 762 Chinese stations, analysis of the probability density distribution of annual minimum air temperature in China showed a clear bimodal distribution. It was found that there are significant regional differences in the distribution of annual minimum air temperature during the East Asian winter monsoon. Inspections of the spatial distribution of the frequency of annual minimum air temperature in the two peaks revealed significant regional differences, which were roughly divided into two climatic zones by the 0℃ line of the long-term mean winter air temperature. By analyzing the date of annual minimum air temperature in the two climatic zones, the boreal winter was divided into an early winter that spans from November 16th to January 15th of the following year, and a late winter that spans from January 16th to March 15th. Following this definition, the interannual variations of early and late winter air temperatures in China were studied by season-reliant empirical orthogonal function (SEOF). Meanwhile, the associated atmospheric stationary and transient waves and their interactions were analyzed based on the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data. It revealed that the first two SEOF modes of surface air temperature from early to late winter depicted the in-phase evolution and the out-of-phase evolution. The spatial morphology of the atmospheric circulation anomaly in early and late winter in the in-phase evolution mode is relatively consistent, and intensity of the circulation anomalies strengthens gradually from early to late winter. However, the atmospheric circulation anomaly in early and late winter in the out-of-phase evolution mode is quite different, as is their spatial morphology. Dynamic and thermal forcing effects of transient waves and the dispersion of the stationary waves play an important role in the maintenance and development of stationary waves from North Atlantic to Eurasia. Waves on the North Atlantic in the in-phase evolution mode spread energy from North America to Europe, which strengthens the European high. Energy dispersions of this center are significantly enhanced in late winter, which forms the wave from Europe to the east of the Kara Sea and further to Lake Baikal. Dynamic and thermal forcing effects caused by atmospheric transient waves make a positive contribution to the maintenance and development of the atmospheric centers of action in Europe and the Baikal area. Characteristics of atmospheric stationary and transient waves and their interactions in early winter in the out-of-phase evolution mode are similar to those in late winter in the in-phase evolution mode. However, the waves in late winter spread from the center of the North Atlantic to Greenland, and further eastward through the Ural region to the northern part of the Tibetan Plateau. Movement of the storm track can lead to abnormal activities of the transient waves, making a positive contribution to the maintenance of the atmospheric centers of action in the southern North Atlantic.