拉萨近半个世纪气温的年际和年代际变化

利用拉萨1952-2005年月平均气温、最高气温、最低气温,及年极端最高气温、极端最低气温,分析了近半个世纪拉萨气温的年际和年代际变化。结果发现:近半个世纪以来,拉萨四季平均气温、平均最低气温均表现为显著的升温趋势,以冬季升温幅度最大。平均最高气温除春季升温不明显外,其它各季均表现为显著的增暖趋势。年平均气温以0.27℃/10a的幅度在升高,年最低气温的升温幅度明显大于最高气温。年平均气温日较差则表现为极显著的减小趋势,这主要是由于最低气温的明显升高引起的。年极端最高气温、极端最低气温也都表现为显著的升高趋势,以极端最低气温升高幅度最大,特别是近25年,升幅达1.26℃/10a。20世纪60年代至今,拉萨平均气温、平均最高气温和最低气温均呈明显的逐年代升高趋势。年平均气温异常偏暖出现在1999年和2005年,异常偏冷发生在20世纪60年代。年平均气温存在准5a、准15a年际振荡和准24a的年代际振荡周期特征。

Interannual and Decadal Variations of Temperature in Lhasa from 1952 to 2005

Using the data of monthly mean temperature(Ta),maximum temperature(Tmax),minimum temperature(Tmin),annual extreme maximum and minimum temperature from 1952 to 2005 in Lhasa of Tibet,the interannual and interdecadal variations of the temperature were analyzed.The results showed that in past 50 years,the seasonal Ta and Tmin displayed significant increasing trend in Lhasa,especially in winter.The increasing trend of Tmax was in all season(except spring).In addition,the warming for annual mean temperature indicated an increase of 0.27℃/10a,annual Tmin increase was bigger than that of Tmax.The trend of annual daily temperature rang was decreasing,and its decrease was because of obviously increasing Tmin.Also,the increasing trend of annual extreme maximum and minimum temperature was obvious,especially in the last 25 years(1981-2005),annual extreme minimum temperature trend indicated an increase of 1.26℃/10a.The interdecadal variations of Ta,Tmax and Tmin increased from 1960s to 2000s,the 1960s was the coldest decade.There were anomalous warm years of Ta in 1999 and 2005,whereas anomalous cold years in the 1960s.The annual mean temperature in Lhasa during recent 50 years had mainly the interannual oscillation periods of quasi 5 years,15 years and interdecadal oscillation periods of quasi 24 years.