The Components of Incoming Radiation within a Mid-Latitude Alpine Watershed during the Snowmelt Season

Field measurements of radiation and temperature are used as input to a digital model that simulates direct and diffuse irradiance on the partial areas of snow cover in upper Green Lakes Valley, Front Range, Colorado. All of the components of incoming radiation are considered and anisotropic radiance distributions are utilized in the computation of diffuse fluxes. The simulated radiation totals indicate that intravalley differences in diffuse irradiance may be large (maximum differences range from 3 to 12 MJ m-2 on an average day during the snowmelt season) and that significant variations can even occur within a single snowfield. Intersite differences in diffuse irradiance often result from subtle variations in slope-aspect and sky dome configuration that are not captured by simplified approximation formulas. The components of incoming radiation combine in a manner that reduces spatial variability, so between-site differences in total radiation income are normally much smaller than a study of the distribution of direct insolation would suggest.