黄河、长江源区降水变化的水汽输送和环流特征

利用黄河、长江源区气象站的降水资料和NCEP/NCAR再分析气候资料,分析了黄河、长江源区降水的年际变化,对黄河、长江源区典型多雨年与少雨年的500 hPa位势高度和风场、600 hPa流场、大气水汽含量和水汽输送进行了合成和对比分析.结果表明:黄河和长江源区的降水在近50 a的长期变化趋势都不明显,但在最近10 a黄河源区的降水有明显的减少趋势.而长江源区的降水则有明显的增加趋势;江河源区在多雨与少雨年有明显的环流差异特征,在多/少雨年,500 hPa蒙古低压减弱/加强,西风风速减弱/增强,600 hPa高原辐合线偏北/南,江河源区大气水汽含量增加/减少,西南季风的偏南水汽输送增加/减少.使得江河源区有较多/少的水汽来源,从而降水增多/减少;黄河和长江源区有相似的多雨与少雨年环流差异特征,只是差异程度不同,长江源区多雨与少雨年环流特征差异的强度不及黄河源区.

Characteristics of Water Vapor Transport and Atmospheric Circulation for Precipitation over the Source Regions of the Yellow and Yangtze Rivers

On the basic of weather station precipitation data and NCEP/NCAR reanalysis data,interannual change of precipitation over the source regions of the Yellow River and the Yangtze River are respectively analyzed.Composite characteristics of the geopotential height and wind field on 500 hPa,the flow field on 600 hPa,the atmospheric water vapor content and water vapor transport for the typical rainiest and rainless years over the source regions of the Yellow River and the Yangtze River are respectively analyzed and compared.The results show that,the long-term change trend of the precipitations over the source regions of the Yellow River and the Yangtze River are not clear during the last 50 years but obvious decreased over the source regions of the Yellow River and increased over the source regions of the Yangtze River during the last 10 years.There are obvious circulation difference characteristics between rainiest and rainless years.In the rainiest/rainless year,the Mongol low pressure on 500 hPa is weaker/stronger and so the westerly speed is weaker/stronger,the Plateau convergence line on 600 hPa moves north /south,the water vapor content over the river source regions increases/decreases,the water vapor transport from south by the southwest monsoon increases/decreases and make more/less water vapor source to the river source regions and so make more/less precipitation.There are similar atmospheric circulation difference characteristics between the source regions of the Yellow River and the Yangtze River for rainiest and rainless years but the circulation difference degree is stronger over the source regions of the Yellow River than over the source regions of the Yangtze River.