1980-2009年西藏地区水汽输送的气候特征

Climate Characteristics of Water Vapor Transport over Tibet Region in 1980-2009

利用1980-2009年NCEP/NCAR月平均再分析格点资料,分析了近30a来西藏地区水汽输送的气候特征.结果表明:1)西边界和南边界为水汽流入边界,北边界和东边界为水汽流出边界;夏季水汽总输入量最大,冬季最小且季节差异显著;春季水汽总输出量最大,冬季最小且季节差异不明显;春、冬季为净水汽支出,夏、秋季为净水汽收入;2)无论是年还是不同季节平均,近30a来西边界水汽输入量、北边界水汽输出量基本呈现增加趋势或弱的减少趋势,东边界水汽输出量、南边界水汽输入量基本呈现减少趋势;总水汽输入、输出量均呈现减少趋势;年、夏季、秋季净收入量呈现减少趋势,春季、冬季净支出量呈现增加趋势;3)西藏地区冬、春、秋季的水汽主要来自中纬度西风带水汽输送,夏季水汽主要来自阿拉伯海、孟加拉湾、南海和西太平洋地区,夏季南边界的水汽输送状况对西藏地区降水起着决定性作用.

In this paper,the climate characteristics of water vapor transport in Tibet Region from 1980 to 2009 are investigated by using NCEP/NCAR reanalysis.It is found that through the west and south boundaries water vapor inputs while through the north and east boundaries water vapor outputs.Total input exhibits significant seasonal variation,large in summer and small in winter.However,total output has insignificant seasonal variation,large in spring and small in winter.The net water vapor balance is minus in spring and winter and plus in summer and autumn.Whatever the annual mean or the seasonal mean water vapor inputs through the west boundary has basically presented an increasing trend,so has the output through the north boundary,but sometimes slight decreasing,and the water vapor output through the east boundary and the input through the south boundary,the total water vapor input or output have presented a decreasing trend in the last 30 years,together with a decreasing trend of the net water vapor income in summer and autumn and annually and an increasing trend of the net water vapor loss in spring and winter.Furthermore,net water vapor income exhibits a decreasing trend in annual mean,in summer and autumn,but an increasing trend of net water vapor expenses in spring and winter.The main water vapor in Tibet Region comes through subtropical westerly transportation in winter,spring and autumn,but comes from Arabic Sea,Bay of Bengal,South China Sea and west Pacific Ocean in summer.The vapor through south boundaries in summer is conclusive for precipitation over Tibet region.