青藏高原西部地表反射率的合成分析

利用中(国)日(本)青藏高原陆面过程合作试验(GAME/Tibet)设立于青藏高原西部狮泉河和改则两地自动气象站(AW S)1997~1998年观测的大气、辐射和土壤等资料,计算了两地的逐时地表反射率,并进行了日平均、月平均和日合成分析,据此讨论了青藏高原西部地表反射率的若干变化特征,并在计算了对反射率影响最大的因子——太阳高度角的基础上,着重讨论了青藏高原西部地表反射率的日变化特征。结果表明:夏半年,由于降水使土壤湿度增大,植被生长、地表反射率值较低;冬半年,受土壤湿度减小、雪盖覆盖影响,地表反射率值较高,12月平均值可达0.5以上。而地表反射率的日变化特征表现为,清晨、黄昏地表反射率高,中午地表反射率低,大致呈U形曲线,与太阳高度角的变化相反。该工作有助于深入了解高原地区地表反射率的平均状况及其变化特征。

The Composite Analysis of Surface Albedo on the Western Tibetan Plateau

By using the continuous observational data of air,radiation and soil from two sites of automatic weather station(AWS) at Shiquanhe and Gaize on the western Tibetan Plateau in the period from September 1997 to December 1998,the hourly surface albedo is computed.Furthermore the daily mean of surface albedo and the monthly mean are computed and analyzed.On the basis of the calculation of the solar elevation angle which is the most significant factor to the surface albedo,the stress of this paper focuses on analyzing the diurnal variations of surface albedo by the method of composite analysis.The result shows that the value of surface albedo is reduced in summer with rain season and obviously increased in winter with dry season(the mean value of the surface albedo exceed 0.5 in December).The diurnal variation of surface albedo exhibits "U" shape.The maximum of surface albedo appears at sunrise and sunset,and its minimum appears at noon,the variation trend between surface albedo and solar elevation angle is reverse.The results are helpful to acquire a deep understanding of the variational characteristics of surface albedo in this area.