近50年西藏冷暖冬的气候变化特征

Climatic Change in Cold and Warm Winter over Tibet during 1961-2010

依据中国国家标准《暖冬等级》,参照单站、区域暖冬等级标准,确定了单站和区域冷冬等级。在此基础上,分析了1961-2010年西藏18个站冷、暖冬事件的气候变化特征。结果表明:近50年西藏各地冬季平均气温呈明显的升高趋势,升幅为0.29～1.04oC/10a,以班戈最大;尤其是近20年升温更强烈,达0.73～2.36oC/10a。西藏区域暖冬指数表现为显著的上升趋势,线性趋势为16.0%/10a,明显高于东北、华北、西北等区域。各站暖冬频率为32%～52%,强暖冬事件频率为6%～26%;区域暖冬共出现了21次(年),其中强暖冬事件10次(年),主要出现在21世纪初;2006年和2009年是50年中范围最广、强度最大的暖冬。各站冷冬频率为18%～40%,强冷冬事件频率为2%～20%;区域冷冬站数约以每10年12%的速率减少。区域冷冬共发生了16次(年),以20世纪60年代居多,其中区域强冷冬事件出现了8次(年),1962年是近50年中范围最广、强度最大的冷冬,1968年和1983年次之。

According to the China national standard,the warm winter is classified into two groups by space and intensity grades.In the space group the warm winter is divided into two spatial grades as single station warm winter,and regional warm winter.In the intensity group,there are two grades as weak warm winter（warm winter） and strong warm winter.Average winter air temperature is divided into three probability categories to define the threshold of warm winter for single station and its warm winter intensity.Then the division criteria for regional winter warm intensity are calculated according to percentile rank of warm winter stations.In accordance with this standard,the grade of single station and regional cold winter are determined.On the basis of the division method for cold and warm winter,the characteristics of cold and warm winter from 1961 to 2010 over Tibet are analyzed.The results show that the mean temperature in winter has increased over Tibet with a rate of（0.29-1.04） o C/10a in recent half century,and the maximum value is in Bangoin.Especially in recent 20 years（1991-2010） ,the warming amplitude becomes stronger with a rate of（0.73-2.36） o C/10a.Regional warm winter index has an obvious rising trend at a decadal rate of 16%,which is higher than that in Northeast China,North China and Northwest China.Frequency of single station warm winter is 32%-52% with 6%-26% of strong warm winters.There are 21 regional warm winter years over the 50 years with 10 strong warm winters,and there are more occurrences of warm winter in the 2000s,while the most extensive and strongest of regional warm winter occurred in 2006 and 2009.The results also show that the frequency of single station cold winter is 18%-40% with 2%-20% of strong cold winters,and that regional cold winter index has a decreasing trend at a decadal rate of 12%.There are 16 regional cold winter years over the 50 years with 8 strong cold winters,and more occurrences of cold winter was observed in the 1960s.Additionally,the year 1962 witnessed the most extensive and strongest regional cold winter,followed by 1968 and 1983.