The Impact Of The “warm Arctic-cold Eurasian” Mode Transition On Extreme Cold Events In Winter In China

In the context of global warming,the "Warm Arctic-Cold Eurasia"(WACE)interdecadal temperature variation pattern appeared in the Polar-Eurasia region.At the same time,winter extreme cold events in China have shown an increasing trend.Studying the relationship between cold events and WACE,and revealing the response mechanism of cold events in China to WACE,will help to improve the level of climate prediction,and provide a reference for disaster prevention and mitigation and scientific response to climate change and its impact.Based on the ERA5 reanalysis data,NCEP\NCAR reanalysis data and 39 climate model data from the Sixth Global Coupling Model Comparison Program,this study investigated the impact of WACE mode transition on winter extreme cold events in China.The result is as follows:(1)Multi-modal ensemble(MME)can better capture the spatial distribution characteristics of WACE.For a single mode,the accuracy of the simulation of the location of the Ural Blocking High(UB)can significantly affect the mode's ability to reproduce the WACE mode.(2)On the interdecadal scale,the WACE mode transition(from WACE-to WACE+)makes the frequency of cold nights(warm days)in winter increase(decrease)and the intensity increase(decrease)in most areas of China,except the Qinghai-Tibet Plateau.The most significant increase(decrease)in the northern region.From the perspective of the intra-seasonal time scale,the extreme events in late winter have the strongest response to the WACE mode transition;in terms of the types of events affected,the WACE mode transition has a much greater impact on cold nights than warm days.(3)The analysis of the influence mechanism showed that the response of the cold event to the WACE mode transition may be related to UB.In WACE+ years,the intensity of UB increased,merged with the Western European Blockade(WEB),and then intruded to the poles,promoting the exchange of cold and warm air,which was conducive to the formation of a warm Arctic-cold Eurasian situation,resulting in an increase(decrease)of cold nights(warm days)in most parts of China).At the same time,the strong UB was maintained stably in the winter of the WACE+ year,and the cold air in East Asia frequently moved southward,which had a significant impact on northern China.(4)Further use the principle of conservation of potential vorticity to explain the reasons why the southward movement of cold air at high latitudes induces the development of low-level cyclones and the strengthening of the East Asian trough during the phase transition of WACE.In the WACE-year,the strong cold air is mostly concentrated in the Arctic region.When transitioning to the WACE+ year,the high potential vortex anomaly at high latitudes gradually strengthens,and travels southward along the isentropic plane,accompanied by the strengthening of the northerly wind.When the abnormally high potential vorticity propagates to the mid-latitudes,the positive vorticity in the middle and lower layers of the atmosphere develops,leading to the deepening of the East Asian trough.Therefore,the cold air broke out to the south,and the cold event in China in the WACE+ year intensified.