Assessment of global climate model land surface albedo using MODIS data

[1] Land surface albedo from the Community Land Model is compared to white-sky (diffuse) and black-sky albedo (direct at local solar noon) from MODIS. Generally, comparisons are more favorable in summer than winter, for visible waveband than near-infrared in regions without snow cover, and for black-than white-sky. In regions with extensive snow cover, the model overestimates white- and black-sky albedo by up to 20% absolute. The snow-free visible and near-infrared black-sky albedo is simulated quite well with biases within +/-5% over most of the land surface. However, a large negative model bias was found for the Sahara Desert and Arabian Peninsula, particularly in the near-infrared. The poorer simulation of white-compared to black-sky albedo in vegetated areas implies that the model may be overestimating the increase of albedo with solar zenith angle. These results identify several areas that should have priority in further evaluating and improving albedo in the model.