The Impact of Barents Sea Ice Concentration on the Interannual Variation of Winter Extreme Cold Days over South China

Abstract 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 in the winter BRSIC tends to be accompanied by an increase in 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 ice-advection feedback. A warmer Arctic elevates the geopotential height at the high latitudes, forming a meridional thickness gradient in the high- and midlatitudes of the Northern Hemisphere. The midlatitude westerly jet over 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 time scales, 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. Significance Statement In February 2008, a catastrophic winter snowstorm struck central and southern China, causing severe impacts on the regional agriculture, infrastructure, and human health. Therefore, the winter extreme cold days (ECDs) over South China are of particular socioeconomic concern. This study underscores the pivotal role of the Eurasian westerly jet stream, closely associated with the Barents Sea ice concentration (BRSIC), in modulating the winter ECDs over South China. This serves as a bridge between the winter Arctic sea ice processes and the midlatitude weather patterns. The present findings reveal that reduced BRSIC is accompanied by enhanced local Arctic warming through coupled feedbacks and, in turn, prolongs the Ural blocking events by weakening the midlatitude Eurasian westerly jet stream. As a result, this would facilitate the southward intrusion of cold air into South China, thereby increasing the local winter ECDs and vice versa. These results have an implication for the impact of the future Arctic sea ice reduction on the winter ECDs over South China under global warming.