西北地区近50a降水变化及水汽输送特征

用NCEP/NCAR再分析资料和中国西北地区145个站的降水资料,研究了西北地区降水与亚洲季风区水汽输送特征的关系。主要结论为:①西北地区降水具有明显的区域性特征,在20世纪80年代以后,西北地区东部降水明显减少,干旱化趋势严重;在西北地区西部,降水增加,气候逐渐向暖湿型转变;②西北地区东部的水汽在夏季主要来自孟加拉湾、南海和西太平洋;西北地区西部除了受西风带的影响外,来自北方西伯利亚的水汽输送在夏季也有一定的作用;③西北地区东部的南边界和西边界是主要的水汽输入,西北地区西部的西边界是主要的水汽输入。在降水偏多年,其水汽输入在7月达到峰值,且具有明显的年变化特征;④西北地区东部的南边界和西边界水汽输入减少趋势明显,使得水汽总收支逐渐减少。西北地区西部西边界的水汽输入自80年代中期以来有增加的趋势,而北边界的输出在减少,水汽总收支有增加的趋势。

Variation of Precipitation and Water Vapor Transport over the Northwest China from 1959 to 2005

NCEP/NCAR reanalysis data and a 47-year precipitation dataset from 145 observation stations had been utilized to analyze the characteristics of variation of precipitation and water vapor transport in Northwest China. The results showed that: (1) Northwest China had different regional climatic characteristics in different areas. The interannual trends of precipitation between the eastern Northwest China (ENWC) and the western Northwest China (WNWC) showed a contrary variation. In the middle 1980s, the precipitation continually decreased in ENWC, but in WNWC the precipitation appeared an upward trend. (2) In summer, the water vapor of the ENWC was mainly from the Bay of the Bengal, the South Sea and the West Pacific Ocean. The northerly Siberia and the middle-latitude westerly water vapor transport had influenced on the WNWC in summer. (3) The western and southern boundaries were the main inflow passports for the ENWC, and the western boundary was the main inflow passport for the WNWC. In more precipitation years, the water vapor flux arrived at a peak point in July and had a obvious interannual change. (4) The water vapor influx into western and southern boundaries appeared downward trend in ENWC, but in WNWC the water vapor influx into the western boundaries was upward in the middle 1980s.