Extreme Cold Events And Interdiural Temperature Variation At The Regional Scale In China Under Global Warming Background

Based on the daily meteorological observations,reanalysis and model datasets,this study investigated the evolution and the causes of the extreme cold events at the regional scale in China via a newly-developed ‘temperature whiplash' index,self-organizing map(SOM)method and climate change partitioning method over 1961-2018 from the perspective of the temperature variability and associated large-scale circulation.Results indicate that large-scale atmospheric circulation patterns associated with extreme cold events over China are divided into four patterns(S1-S4)by using the SOM method.The S1 is characterized by a positive anomaly center near the Ural Mountains,with a negative anomaly center over Northeast China,while S2 features a positive anomaly center near the Sea of Okhotsk.For S3,its spatial pattern is similar to that of S1,but much weaker in amplitude,while S4's signs are just opposite to that of S1.During 1961-2018,the significant reduction of extreme cold events in eastern China was mainly due to the significant reduction of extreme cold events under the S4(high-south-low-north)pattern,and the thermodynamic contribution was greater than other parts.With the approach of time,especially since the 1990 s,the significant increase in extreme cold events in eastern China,especially in Northeast China,is due to the significant increase in extreme cold events under the S1(high-northlow-south)pattern,and the dynamic contribution was greater than other parts.Finally,the model evaluation shows that the Had GEM3-A-N216 ensembles have a better performance on the main characteristics of S1 and S4 patterns,especially on pattern frequency.Further,the attribution analysis of the frequency change in circulation patterns by using Had GEM3-A-N216 ensembles shows that the observed changes in the frequency of circulation patterns cannot attribute to the anthropogenic forcing,therefore,it is likely that observed changes in the frequency of circulation patterns can attribute to internal variability,or there are some deficiencies in the model simulating the changes in the frequency of circulation patterns.Also,winters in most areas of China have become increasingly volatile during 1980-2018 based on the interdiural temperature variation.This enhanced volatility has a strong expression in significant increases in whiplash events,which characterizes rapid and drastic switches between warm and cold extremes within several days.At the same time,there was a significant relationship between the increased cold extremes in some areas of eastern China and the enhanced volatility,in which cold extremes are more likely to occur in the form of the whiplash events under global warming background.Although preferentially occurring in the era of Arctic sea-ice melt under global warming background,the magnitude of enhanced volatility still lies within the range produced by atmospheric internal variability,leaving the forcing role of anthropogenic warming non-detectable.