Contrasting the main processes for snow albedo reduction in High Mountain Asia and Colorado.

Snow albedo is a key parameter governing the surface energy budget of the Earth system. Reduction in snow albedo enhances surface warming and accelerates snow cover melt, which has important consequences for regional climate and the hydrological cycle. Snow albedo is characterised by the physical and optical properties of snow grain, such as size, shape, and concentration of light-absorbing impurities (LAI). Often, global climate models (GCMs) have very simplistic treatments of LAI and snow albedo. Here, we extend the range of application of existing parameterisations to better treat the interaction of snow properties and LAI in two contrasting mountain ranges. In this work, the concentration of LAI in surface snow estimated by the GFDL atmosphere-land model (AM4-LM4) is used to investigate the applicability of various snow albedo parameterisations by comparing the results with radiative transfer model at Mera glacier, Nepal, a region that have a storm-driven snow cover and influenced by air masses mainly from Central and South Asia, and at Senator Beck Basin, Colorado, an alpine site with sustainable seasonal snow with dust sourcing primary from the Colorado Plateau. The albedo reduction due to LAI can be up to 3-fold difference between parameterisations: some provide good estimation with relatively clean and fresh snow while some perform better with darker melting snow. Therefore, for global application, a combination of parameterisations is required to cover the entire range of snow conditions.