Changes Of Extreme Low Temperature In Northern China And Its Projection Under 1.5/2? Global Warming

Based on the CN05.1 data set of the daily temperature,NCEP reanalysis data and NCAR CESM model data,the inter-annual and decadal variation of the extreme low temperature of1961-2016 in the northernChina were analyzed by six extreme low temperature indices and percentile thresholdmethod.Its relationship with the atmospheric circulation changes is studied,and the change of the extreme low temperature in the northern China under1.5 /2 ?global warming,the probability ratio and the avoided impact are estimated.The following main conclusions are obtained:(1)The extreme low temperature threshold of northern China in winter is zonal,and decreases with the increase of latitude.The center of extreme low value is in the northeast of China,reaching-40 ?.In recent decades,there is a consistent warming trend in the whole northern region.The long-term variation of the winter extreme low temperature days in Northeast,North China and Northwest China shows a downward trend,and the inter-decadal abrupt change occurred in 1980 s.The minimum of daily maximum temperature and minimum temperature of North China and Northeast China are both 0.3 ? / 10 a and 0.5 ? /10 a,and the number of cold days in Northeast China is 0.4 days / 10 a,while that of Northeast China is 0.4 days / 10 a,and the minimum value of daily maximum temperature and minimum temperature is relatively large in North China and Northeast China.The decreasing trend of cold night days in North China is 2 days / 10 a,the duration of low temperature is 0.7 days /10 a in North China,and the largest decreasing trend is 0.4 ? / 10 a in northeast China.(2)There is a significant positive potential height anomaly in the upper polar region of 500 hPa when the intensity and frequency of extreme low temperature are strong,and the sea level pressure in the polar region is a significant positive anomaly,indicating that the polar vortex is weak.However,there is a significant negative temperature anomaly in most regions of the polar region,and the cold air tends to fall south with the polar vortex splitting.There is a significant negative anomaly of potential height in the East Asian trough region,which deepens the East Asian trough and strengthens the intensity,which leads to a strong intensity of extreme low temperature in northern China as a whole.The correlation coefficient between AO index and extreme low temperature index indicates that the negativephase of AO corresponds to the low intensity of extreme low temperature,high frequency of low temperature and long duration of low temperature in northern China in winter.Moreover,AO has the greatest influence on the northeast of China.There is also a significant positive sea ice anomaly between the east of Greenland and the East Siberian Sea in the autumn when the extreme low temperature is strong in northern China.The correlation coefficient between the key sea areas and the frequency of extreme low temperature is as high as 0.6,which indicates a significant positive correlation between the sea ice concentration and the frequency of extreme low temperature.The correlation coefficients between sea ice concentration time series and extreme low temperature intensity and frequencyare-0.48 and0.55,respectively.(3)Compared to the preindustrial level,the whole of China will experience0.32–0.46 ? higher minimum surface air temperature(SAT)warming than the global average SAT,and the winter temperature increase in northern China is the most pronounced over the country.In almost all the regions of northern China,especially Northeast and Northwest China,extreme low temperature events will occur with lower intensity,frequency,and duration.Compared with the present day,the intensity of low temperature events decreases most in Northeast China,with TXn increasing by 1.9/2.0 ? and TNn increasing by2.0/2.5 ? under 1.5/2 ? global warming,respectively.The frequency of low temperature events decreases relatively more in North China,with TX10 p decreasing by 8 days/ 11 days and TN10 p decreasing by 7 days/ 9 days under 1.5/2 ? warming.CSDI decreases most in Northwest China,with decreases of 7 days/ 10 days with 1.5/2 ? warming.DTR decreases in the Northwest and Northeast but increases in North China,with-0.9/-2.0 ? in the Northwest,-0.4/-1.5 ? in the Northeast,and 1.7/2.0 ? in North China in the 1.5/2.0 ?warming scenarios.Global warming of 2 °C instead of 1.5 °C will lead to extreme low temperature events decreasing by 6%–56% in regard to intensity,frequency,and duration over northern China,and the maximal values of decrease(24%–56%)are seen in Northeast China.