Characteristics and Causes of Intraseasonal Variation of Winter Temperature in China under Different Interdecadal Scale

This study investigates the intraseasonal variation characteristics of winter temperature in China and related atmospheric circulation anomalies under two different interdecadal time scale stages, classified as before and after 1986, using observed temperature data in China from 1951 to 2020, NCEP/NCAR reanalysis dataset, and statistical methods. The proportion of anti-phase years of temperature in early winter (December) and late winter (January–February) is higher in each stage than in the same phase years. Furthermore, the season-reliant empirical orthogonal function (S-EOF) method was used to obtain the dominant modes of the interseasonal variation in winter under two interdecadal time scale periods. Before 1986, the dominant spatial mode in winter showed that the national cold (warm) in early winter was likely to change to the warm (cold) in southern China in late winter, implying that the intraseasonal variability in the southern region was greater than that in the northern region. After 1986, the dominant spatial mode is more likely to demonstrate that the cold (warm) in northern China in early winter changed to the obvious warm (cold) in the entire country in late winter, indicating that the intraseasonal variability in the northern region is greater than that in the southern region. The interseasonal variation of winter temperature is significantly affected by the interseasonal variation of the key circulation of the East Asia winter monsoon system. Before 1986, the tropospheric circulation anomaly signal in the middle and high latitudes of Eurasia weakened significantly from early winter to late winter, correlating to the positive phase anomaly years of the dominant mode. The circulation adjustment in the middle and upper troposphere was more prominent in the Northwest Pacific, the subtropical height field was enhanced, and the tropical easterly jet expanded northward. The circulation adjustment in winter is conducive to the country-wide cold in early winter, while warm in southern China in late winter, resulting in strong intraseasonal variability in the southern region. After 1986, the circulation anomalies in the high, middle, and low latitudes of Eurasia increased significantly from the early winter to the late winter, and the circulation in the middle and high latitudes of Eurasia adjusted significantly, while the circulation in the low latitudes changed little. The northern region of China was cold in the early winter, warm in the late winter, and the intraseasonal variability was greater than in the southern region. The subtropical circulation and the mid-high latitude circulation play major roles in the intraseasonal variability of southern and northern China in the two interdecadal scale stages (before and after 1986), respectively.