Research On The Abnormal Characteristics And Mechanism Of The Intensity Of Winter Cold Waves In Northern China In The Past 40 Year

Based on the daily minimum temperature data from 1980 to 2019 provided by the National Meteorological Information Center(China),the monthly reanalysis data from NCEP/NCAR,the monthly sea surface temperature(SST)the sea ice density data provided by Hadley Center(UK),the spatio-temporal characteristics of the intensity anomaly of cold waves in the winter of northern China are analyzed,and the impact of changes in the intensity and location of the Eurasian teleconnection pattern(EU)on the cold wave was further discussed.The influence mechanisms of the mid-latitude SST anomalies(SSTA)in the northern hemisphere and Arctic sea ice on it are also investigated.The results show that:(1)There are interannual and interdecadal variations in the single-station cold wave intensity in northern China.The interdecadal changes in cold wave intensity are more pronounced before 1998,and interannual variability is greater after 1999.The cold wave is strongest in North China,followed by the junction of Inner Mongolia,Gansu and Xinjiang.The distribution of cold wave intensity mainly includes regional consistent type,east-west reverse phase type,and tripolar type anomalies.The regional consistent type anomaly can basically reflect the overall spatiotemporal variation characteristics of cold wave intensity.The intensity of the cold wave has shown a weakening trend in most areas of northern China,and an upward trend in Xinjiang,western Inner Mongolia,and parts of Northeast China.(2)In the winter of 1980—2019,there were stationary wave activities related to EU over the Eurasian continent,and the upstream energy supplement maintained the anomalous center of the wave train.When the EU is relatively strong,it will cause a strong cold wave in most areas of northern China.The spatial distribution of cold wave intensity will vary with the location of the geopotential height anomaly center near Lake Baikal in the EU.The high value region of cold wave intensity in 1999—2012 is northward relative to 1980—1991,and the low value region of cold wave intensity in 2013—2019 is westward relative to 1992—1998.(3)The regional consistent anomaly of cold wave intensity is closely related to the North Pacific SSTA from pre-spring to winter and the North Atlantic SSTA from pre-autumn to winter.The "-PDO"-like SSTA in the North Pacific from pre-spring to pre-autumn and negative SSTA in the North Atlantic from pre-autumn to winter can trigger the winter teleconnection or wave train anomalies,such as the negative Arctic Oscillation("-AO"),positive Eurasian teleconnection("+EU"),Pacific-North America("PNA")-like pattern,negative North Atlantic Oscillation("-NAO").In pre-autumn and winter,the interaction of two oceans makes the upstream Rossby wave energy dispersing downstream,and continuously strengthens the "+EU",resulting in Ural Mountain ridge and East Asian trough stronger.Along with the cooperation of300 h Pa jet stream that is weak in the north and strong in the south,it will facilitate the southward movement of cold air from high latitude and accumulation in northern China.The coordination of the high-and low-level anomalous circulation leads to an enhancement of the cold wave intensity in northern China.The changes in the sea ice in the northern part of the Severnaya Zemlya and the western part of the Beaufort Sea in the pre-summer,and the sea ice near Novaya Zemlya in pre-autumn are closely related to the regional consistent anomaly of winter cold wave intensity.The changes in the sea ice in key regions will trigger wave train anomalies in Eurasia,in conjunction with weak north to strong south jets,low-level northerly winds,and cold air heaps,resulting in an increase in cold wave intensity.