Characteristics Of Winter Low Temperature Events Changes And Its Relationship With The Arctic Sea-ice In The Mid-latitudes Of Eurasia Past 30 Years

Using ECMWF reanalysis datasets and NOAA/NCDC station datasets, we constructed a new coldness intensity (CI) index based on the amplitude of daily anomalously cold temperatures in winter, and calculated winter low temperature events and temperature advection on Eurasia. We analyzed the characteristics of frequency of winter cold events and the reason of it in the mid-latitudes of Eurasia during 1979-2013, and its trend past 16 years. In addition, revealing the relationship between autumn Barents-Kara sea ice extent and winter air temperature of China.The results show that:(1)The frequency of winter cold events decreased in the late 1980s, the 1990s and the early 2000s, but increased in the early and middle 1980s, especially a significant increase in cold days and cold nights emerged after the mid-2000s in the mid-latitudes over Eurasia. Severe low temperature events in winter frequently also occurred in mid-latitudes of Eurasia past 16 years. In addition,the variation in the winter coldness intensity greatly resembles the change in the frequency of cold days and cold nights compared with the intra-seasonal temperature variance, indicating that the recent frequent low temperature extremes can be well manifested by the intense coldness in the past few years.(2) Recent frequent and persistent cold surges facilitate the significant decreasing of winter temperature over the mid-latitudes of Eurasia together with continuously strengthening of winter coldness intensity. In the meantime, synoptic anticyclone during winter dramatically intensified, the continuous intensification of Siberian High associated with enhancing northerly wind and weakening westerly wind in the mid-latitudes of Eurasia. And the first two leading modes of the Northern Hemisphere winter extratropical circulation also made Siberian High increased recently, leading to negative winter temperature anomalies over mid-latitudes.(3)We found that the temperature advection is mainly dominated by cold advection in the mid-latitudes of Eurasia, both zonal and meridional advection play important part in cold events occurred more and more frequently. Besides the meridional wind and temperature gradient components cooling effect, the zonal wind and temperature gradient components also play a particularly significant role in cold anomalies in the mid-latitudes. However,the dominant components for temperature advection varies at different regions. In particular, the meridional wind and temperature gradient components dominate in Siberian region, while the zonal wind component drives cooling effect make over European, and the zonal temperature gradient play a key role cooling over East Asian.(4) When the autumn Arctic Kara-Barents sea-ice extent diminished, winter Siberian High increased, the near-surface winter south-north temperature gradient and the winter atmospheric baroclinic are significantly weakened, and winter anticyclone activities are persistent and frequent, which caused winter continuous cooling in the mid-latitudes of Eurasia. This suggests that changes of autumn Arctic Kara-Barents sea-ice extent may serve as a predictor of winter temperature changes in China.