青藏高原“三江源地区”雨季水汽输送特征

利用40年NCEP/NCAR再分析资料和青藏高原三江源地区的降水资料,分析了三江源地区的水汽输送特征.研究表明:在东亚和印度季风驱动下的西南暖湿气流是三江源地区空中主要水汽来源,其次是来自西边界中东高压中的偏西气流和西风带中的偏北气流,这3种大尺度环流背景的气流汇集到三江源区,使该地区6-9月处在水汽辐合区内,同时在高原大地形的动力作用下,三江源地区近地面层维持定常的切变、低涡等天气系统,源源不断的降水为这一区域形成江河源头创造了条件.在水汽输入的各边界中,南边界季节变化特征显著,冬、春季水汽输入量小,夏、秋季水汽输入量大,9月达到全年的最大值.西边界的水汽输入量季节变化特征不明显,一年四季有水汽输入.北边界冬、春季水汽输入量小,夏、秋季水汽输入量大,6月达到全年的最大值.水汽输出主要在东边界.从三江源地区空中净水汽输入(输出)量收支的月际变化来看,6-9月水汽是收入的,5月收支平衡,10月到次年4月水汽是支出的,三江源地区的这种净水汽输入(输出)量收支的月际变化与该地区降水量的月际变化基本一致.冬、春季以西边界的水汽输入为主,夏、秋季以南边界的水汽输入为主.青藏高原三江源地区主要水汽输入边界的水汽通量近40年来呈现减少的变化趋势,这将影响到三江源地区未来的降水变化.

The climatic characteristics of vapor transportation in rainy season of the origin area of three rivers in Qinhai-Xizang Plateau

Using NCEP/NCAR data and 40 years precipitation data of Qinhai Xizang Plateau meteorological stations. The results showed that the main water resource of the origin area of three rivers (Changjiang, Huanghe, Lancangjiang) in Plateau is the southwest wet airflow by East Asia and Indian monsoon and the secondly is the west airflow from Middle Asia high pressure of west boundary and the third one is the north airflow in the westerlies. These three different airflows of large-scale circulation background influx to the three rivers in Plateau and make thisregion lie in the convergence area of vapor from June to September. At the same time the ground layer of the source of three rivers in Plateau maintain stationary weather systems such as shear and vortex and so on under the dynamic effect of large topography of Qinhai-Xizang Plateau and form the source of rivers in this area being perpetual rainfall. The vapor flux of main importing boundary of the source of three rivers in Plateau present descending trend in near 40 years and will influence on the precipitation change of the origin area of three rivers in the future.