Research On The Variation Characteristics And Influencing Factors Of Severe Winter Cooling Events In China In The Past 60 Years

This paper uses Chinese ground station data,NCEP/NCAR reanalysis data,NOAA sea surface temperature data and Hadley Center sea ice density data from 1960 to 2020 to analyze the characteristics of different levels of cold air in winter in China,explore the characteristics of atmospheric circulation anomalies for different types of extreme cold events(ECE),and study the possible influence of Arctic sea ice and northern hemisphere SST on the frequency changes of different types of ECE.The results show that:(1)There is little difference in the distribution of the frequency of general cold events from north to south,and the duration is longer in the north than in the south;the frequency of ECE is more in the north than in the south,the duration is longer in the south than in the north,and the cooling amplitude is greater in the south than in the north,and the frequency has decreased in most parts of the country in recent 61 years.According to the spatial and temporal characteristics of ECE frequency,ECE can be divided into national type(NT ECE),north-south inversion type(N-S ECE)and northeast-north China inversion type(NE-NC ECE).(2)The anomaly of NT ECE is significantly correlated with SST inversion phase changes in the northern Indian Ocean-South China Sea and the eastern Atlantic Ocean in winter,as well as with the first mode in the key area of Arctic sea ice change in the early spring,summer and winter during the same period.Low winter sea ice in the Greenland and Barents Seas and cold SSTA anomalies in the eastern subtropical Atlantic can excite Eurasian positive phase(+EU)remotely correlated wave trains,resulting in the development of a high-pressure ridge in northern Asia,a strong easterly East Asian trough,weakened polar frontal rapids,and strong subtropical rapids.The Siberian high(SH)is weak in the north and strong in the south of Asia,while the Aleutian low(AL)is stronger and located to the west than average,guiding cold air down from the Taymyr and Laptev Sea;the anomalously warm SST in the Indo-South China Sea is conducive to strengthening the meridional circulation between the South China Sea and central Siberia,allowing northerly wind anomalies in East Asia to extend southward to the South China Sea region,resulting in a consistent high frequency of NT ECE in winter.(3)The anomaly of N-S ECE are related to the low-latitude SST anomalies in the Northern Hemisphere and the second mode of Arctic sea ice change from spring to winter in the early period.In winter,the colder SST anomalies in the northern Pacific and Atlantic at low latitudes in the northern hemisphere and the positive phase of the second mode of Arctic sea ice change can excite the +EU-like wave train,but the centre of the anomaly is more westward,the Ural Mountains high pressure ridge and the East Asian trough are stronger and more westward,and the cold air from Novaya Zemlya and the Taimyr Peninsula affects the north southward,while the south is affected by the southerly wind anomaly,and the ECE frequency is low.(4)The high frequency of ECE in the northeast China and low frequency in the north China is associated with the "reverse C" positive phase in the North Pacific Ocean and The "reverse C" Negative phase in the North Atlantic Ocean.This anomaly also excites the +EU wave train,but the wave train is more northerly,and 500 h Pa high-pressure ridge is located to the west and north than average,and a strong eastward East Asian trough,with cold air from the Laptev Sea and East Siberian Sea to the northeast,while southerly wind anomalies cause by weak cyclonic circulation anomaly in central Mongolia and strong northerly subtropical high pressure make frequency of ECE in north China less.