Characteristics Of Extreme Low Temperature In China In Winter And Its Projections Under Global Warming Of 1.5? And 2?

Based on temperature data of 691 non-missing value stations with homogeneity processing from 1961 to 2014 in China,NCEP/NCAR reanalysis data and CMIP5 climate model data,we calculated several indices of extreme low temperature and then analyzed the changes of extreme low temperature in winter in China and its relationship with Mongolia High through climatic statistical methods.Furthermore,characteristics of annual and winter temperature in China under global warming 1.5? and 2? were discussed.Main conclusions of this study are as follows.Cool days,cool nights,frost days and ice days have decreased in most part of China,in particular in the southern part of Northwest China,North China,the eastern part of Northwest China,East China,Central China,Southwest China and plateau regions,with the trends of-0.9d/10a,-1.7d/10a,-1.5d/10a and-1.4d/10a,respectively.The maximum Tmin and minimum Tmin in winter have increased across the country,with the trends of 0.4 ?/10a and 0.6?/10a,respectively;Days of extreme low temperature have fluctuated during 1960s to mid-1970s,then have demonstrated a downward trend from late 1970s and early 1980s to the beginning of 21 century and the decline starts to slow down since 2006,which is a response to global warming hiatus.The number of extreme low temperature days in most regions of China is positively correlated with the intensity and area of Mongolia High while extreme low temperature is negatively correlated to the change of intensity and area about Mongolia High.Areas with much more significant correlation are concentrated in the north part of northeast,east part of northwest region,central China,and southwest region.When Mongolia High is stronger and has a larger activity area above the average,the pressure of Eurasia shows a positive anomaly.Large troughs in East Asia deepen and ridges intensify in higher level,in addition there is downward airflow in the Siberian region correspondingly.As a result,the temperature near surface decreases and the anticyclone anomalies can then lead to colder air in the high latitudes of northern area move towards south,resulting in cooling with different level in most parts of China and even extreme cold events in severe cooling areas.However when Mongolian High's intensity is weak and the activity area is smaller than the average value,it would have little effect on winter temperature and extreme low temperature in China.With the year of 1850-1900 as the baseline period,the time period for the RCP4.5 scenario to reach global warming of 1.5? is from 2017 to 2036,and the time period to reach global warming of 2? is from 2037 to 2059 while the time period to reach global warming of 1.5? is from 2016 to 2030 and the period of global warming of 2 ? is from 2031 to 2044 under the RCP8.5 scenario.The warming range of mean temperature in China during the period of global warming of 1.5? and 2? is greater than 1.5? and 2? respectively,indicating that warming degree in China exceeds the global mean.At the periods of global warming of 1.5?and 2?,mean temperature along with maximum and minimum temperature all increase across the country.The warming range of minimum temperature is greater than mean temperature and maximum temperature.The degree of warming in northern China and the Tibetan Plateau is greater than that in south China.The regions of the most significant warming are concentrated in the northwestern part and Tibetan Plateau.Moreover,temperature increase in winter is greater than annual while with larger regional differences.