Climate Change of the Cold Wave Frequency of China in the Last 53 Years and the Possible Reasons

By virtue of the 740 stations daily surface temperature data in China from 1951 to 2004,the climatology and the climate change of the cold wave frequency of China are analyzed and the possible reasons for the climate change of it are further discussed in this paper.Firstly,a cold wave is defined according to the difference between the maximum and the minimum daily temperature and the anomaly of the minimum daily temperature from its climatological 10-day mean temperature during the period of the activity of a cold air.Then the temporal and spacial distributions of the cold wave frequency of China are revealed.Cold waves of China occur mainly in autumn,especially in November.But the temporal distributions of cold waves between southern China and northern China are not all the same.The cold waves are relatively more in spring than in autumn in southern China,with the situation being opposite in northern China.The cold waves occur mostly in northern China,especially in northern Xinjiang and middle Inner Mongolia,being over 10 times per year on average.There were 371 regional and countrywide cold waves of China from 1951 to 2003,including 104 countrywide ones.Further analyses are processed and the main conclusions are as follows: In recent 53 years,cold waves in most stations of China decreased significantly,especially in Northeast China.As for the countrywide cold wave and the regional cold wave,both of them decreased obviously and their linear trend coefficients are-0.031 times/year and-0.063 times/year,respectively.The regional cold wave in northern China decreased most,with its linear trend coefficient being-0.071 times/year.The cold wave began to decrease in the 1960s and changed abruptly in the late 1970s.The decreasing trend is most significant in winter and least significant in spring.On the basis of analyses about climatology and climate change of the cold wave frequency of China,the possible reasons why they have changed are discussed by correlation analysis.In winter,the strength of Siberian high has a positive correlation with the frequency of regional and countrywide cold waves of China.The weakening of Siberian high mainly resulted in the decrease of their total number.Under the background of global warming,the surface temperature of China and the temperature of the cold mass over Siberian high have increased evidently in the last 53 years.And they both have the negative correlation with the cold wave frequency,especially in autumn and winter and in northern China.They may explain directly why the cold wave frequency of China decreased,the gale frequency having being decreased accordingly.And,it may cause the increase of the surface temperature of China,especially in northern China,that Siberian high and the winter monsoon have weakened in the last 53 years on different degree.They have important impacts on the cold wave frequency of China through the change in temperature.