Snow Albedo's Dependence on Solar Zenith Angle from In Situ and MODIS Data  

作　　者：Zhuo Wang Xubin Zeng 

机构地区：[1]Department of Atmospheric Sciences, The University of Arizona, Tucson, AZ, USA

出　　处：《Atmospheric and Oceanic Science Letters》2008年第1期45-50,共6页大气和海洋科学快报（英文版）

基　　金：supported by NOAA (NA07NES4400002);NASA (NNG06GA24G)

摘　　要：Since snow cover is one of the fastest modifications to the land surface albedo, the treatment of snow-covered surface albedo is important for the simulation of land processes in weather and climate models. A simple formulation is developed here to represent the solar zenith angle (SZA) dependence of albedo under maximum snow cover condition on the basis of Moderate Resolution Imaging Spectroradiometer (MODIS) Bidirectional Reflectance Distribution Function (BRDF) algorithm. The SZA dependence of black-sky (or direct) albedo is weaker under snow condition than that under snow-free condition, and it does not differ much among different vegetation types. The blue-sky albedo (or combined albedo from direct and diffuse radiations) based on the above formulation and in situ diffuse ratio of solar radiation is consistent with in situ data from two Canadian sites (grassland and evergreen needleleaf forest) and one U.S. grassland site. In particular, the SZA dependence of bluesky snow albedo is almost always weak because of high diffuse ratios for high SZA in winter. With the snow albedo formulation from this study and snow-free albedo formulations from the authors' previous studies, albedos with partial snow cover can be obtained as the snow frac- tion-weighted average of snow and snow-free albedos.Since snow cover is one of the fastest modi- fications to the land surface albedo, the treatment of snow-covered surface albedo is important for the simulation of land processes in weather and climate models. A simple formulation is developed here to represent the solar zenith angle （SZA） dependence of albedo under maximum snow cover condition on the basis of Moderate Resolution Imaging Spectroradiometer （MODIS） Bidirectional Reflectance Distribution Function （BRDF） algorithm. The SZA dependence of black-sky （or direct） albedo is weaker under snow condition than that under snow-free condition, and it does not differ much among different vegetation types. The blue-sky albedo （or combined albedo from direct and diffuse radiations） based on the above formulation and in situ diffuse ratio of solar radiation is consistent with in situ data from two Canadian sites （grassland and evergreen needleleaf forest） and one U.S. grassland site. In particular, the SZA dependence of blue -sky snow albedo is almost always weak because of high diffuse ratios for high SZA in winter. With the snow albedo formulation from this study and snow-free albedo formulations from the authors＇ previous studies, albedos with partial snow cover can be obtained as the snow fraction-weighted average of snow and snow-free albedos.

关 键 词：snow albedo MODIS land model 

分 类 号：P461.6[天文地球—大气科学及气象学]