The impact of Barents Sea ice concentration on the interannual variation of winter extreme cold days over South China

The occurrences of the winter extreme cold days (ECDs) over South China could often cause serious damages to the regional economy and livelihoods. Therefore, understanding their interannual variability is of broad scientific and socioeconomic interest. Based on the observation and reanalysis datasets, this work explores the effect of Barents Sea ice concentration (BRSIC) on the winter ECDs over South China during the period of 1978-2020. The results show that the interannual variation of the winter ECDs over South China is closely associated with that of BRSIC. An interannual reduction of the winter BRSIC tends to be accompanied with an increase of the ECDs over South China, and vice versa. Specifically, the BRSIC reduction is closely coupled with Arctic warming through the positive ice-albedo feedback, ice related moisture-latent heat release and the ice-advection feedback. A warmer Arctic elevates the geopotential height at the high-latitudes, forming a meridional thickness gradient in the high- and mid-latitudes of the Northern Hemisphere. And the midlatitude westerly jet over the continental Eurasia would be weakened consistent with the thickness gradient (thermal-wind relationship), providing favorable background conditions for the long duration of Ural blocking events. As a result, under the equivalent barotropic atmospheric conditions, the prolonged Ural blocking events generate anticyclonic winds near the surface at both synoptic and climatological timescales, which could persistently transport cold air to South China, thereby increasing the local winter ECDs. In addition, the sensitivity experiments and climate model simulations have both confirmed this significant result. This study highlights the important role of the Eurasian westerly jet stream and long Ural blocking duration events in the impact of the winter Arctic sea ice processes on the extreme weather events over South China.