Physically based snow albedo model and satellite retrieved snow parameters

The mechanisms to control the radiation budget on snow/ice surface are important for accurate climate simulation of the cryosphere. Since the snow albedo is one of the most important parameter to control the radiation budget on snow/ice surfaces, an understanding of physical process of snow albedo and the modeling (and/or the parameterization) is necessary. Snow albedo essentially depends on snow impurities (water-insoluble solid particles contained with light absorption), snow grain size, geometric illumination condition, and the atmospheric condition for optically thick snow case. Black carbon (BC) on snow surface could reduce the albedo and its climate forcing is reported to be 0.1 W/m2 in the latest IPCC 2007 report. However, large uncertainties are contained in the estimated value.
We developed a physically based snow albedo model, which predicts the visible and near infrared albedos as functions of the concentrations of BC and mineral dust in the snow, snow grain size, and solar zenith angle. The snow impurity concentrations are calculated from wet and dry depositions of these atmospheric aerosols using a chemical transport model, in which the physically based snow albedo model is incorporated. Our climate simulations indicates that the (BC + dust) forcing is much larger than the sum of BC forcing and dust forcing due to the nonlinear albedo reduction depending on those snow impurities. Such snow albedo reduction caused by snow pollution may enhance the recent snow/ice melting in the Arctic. On the other hand, such the snow parameters treated in a physically based snow albedo model as snow grain size, mass fraction of snow impurities, and snow albedo, recently successfully retrieved from satellite data. Availability of these satellite products is discussed with the results of climate simulation for the effects of snow impurities.