Analysis of euphotic depth in snow with SNICAR transfer scheme

Abstract

Solar radiation in the visible spectrum can penetrate through snowpack to a considerable depth, which is named as the euphotic depth in snow. If the snow depth is no greater than the euphotic depth, the surface albedo is greatly affected by the underlying surface. This study defines the euphotic depth as the depth where the residual solar radiation in snow began to be less than 1.0 W m−2 and provides a convenient approach to estimate it. A two-stream, multilayer radiation penetration model (SNow, ICe, and Aerosol Radiation) was applied to predict the vertical profiles of solar radiation based on regular measurements of snow pits and downward solar radiation at Col de Porte (CDP), France from 1993 to 2011. The euphotic depth in snow at CDP exhibits clear seasonal variations, with median values in winter months of 6.8, 8.8, and 10.5 cm, and those in spring remaining nearly on the same level (24.4 and 24.2 cm). The maximum euphotic depth at CDP reached as deep as 78 cm. Further analyses demonstrated that the euphotic depth in snow is related to not only the external initial solar irradiance but also the interior snow extinction coefficient. Stronger illumination and smaller snow extinction coefficients may correspond to greater euphotic depths in snowpack.