Relationship of Ural Blocking Zonal Width to Cold Air Intrusion in China under Varying Barents–Kara Sea Ice Conditions

The zonal width of the Ural blocking (UB) is a potentially crucial characteristic related to cold events in Eurasia. While most studies focus on the intensity, duration, frequency, and mobility of blocking events, the importance of UB zonal width has often been overlooked. Against the backdrop of the declining Arctic sea ice concentration (SIC), the changes in UB zonal width and their association with winter extreme cold events in China remain unclear and require further investigation. This study defines the UB zonal width as the longitude difference between the easternmost and westernmost points of the 120-gpm contour line in the 500-hPa geopotential height (Z500) anomaly field. Based on the NCEP/NCAR reanalysis data and SIC observations during 1970–2020, the UB width and cold air events under varied SIC conditions are examined. It is found that as SIC decreases in the Barents–Kara Sea (BKS), the UB extends zonally, coinciding with the transition of the North Atlantic Oscillation (NAO) from its positive to negative phase. Additionally, linear baroclinic model (LBM) simulations indicate that as the BKS warms, the zonal width of the UB broadens. Concurrently, warming sea surface temperatures (SST) in the BKS lead to decreased 500-hPa zonal wind (U500) and meridional potential vorticity gradient (PV_y) over mid–high latitudes in Eurasia. As a result, energy dispersion weakens and nonlinearity strengthens in the Ural region, resulting in a more zonal extension of the UB. Consequently, the frequency of winter cold events of varying intensities in China increases, such as high-to-low latitude (H–L) and middle-to-low latitude (M–L) cold events. For H–L cold events, both intensity and frequency are higher during low SIC years when the UB widens. Conversely, for M–L events, there is no significant difference in the relationship of UB and cold air intrusion between high and low SIC years. Overall, reduced BKS SIC leads to a more zonal extension of the UB, facilitating the southward movement of cold air and influencing southern China.