CLIMATE AND ENERGY EXCHANGE AT THE SNOW SURFACE IN THE ALPINE REGION OF THE SIERRA-NEVADA .2. SNOW COVER ENERGY-BALANCE

A detailed evaluation of surface climate and energy exchange at the snow surface in a small alpine watershed, typical of much of the southern Sierra Nevada, is presented for the 1986 water year. Measurements of snowfall, meteorological and snow cover conditions, and snow cover ablation, described in part 1 of this paper (Marks et al., this issue), are used to characterize the climate. Each form of energy transfer, radiation, sensible and latent heat flux, soil heat flux, and heat flux by mass advection, is evaluated separately to determine how its magnitude changes during the snow season. These are then combined to approximate a snow cover energy balance and determine the relative importance of each form of energy transfer in the seasonal energy and mass balance of the snow cover. Radiation and sensible and latent heat flux dominate the snow cover energy balance throughout the snow season. During snowmelt, radiation accounts for between 66 and 90% of the energy available for melt. Sensible and latent heat transfer during this time are of approximately equal magnitude but are usually of opposite sign and therefore cancel. Calculated sublimation during the entire snow season accounted for the loss of about 20% (approximately 50 cm snow water equivalent) of the mass of the snow cover. This experiment shows that energy and mass transfer can be adequately monitored at a remote site using a combination of measured and modeled parameters and that the energy balance of the snow cover in the alpine zone of the Sierra Nevada is dominated by net radiation during snowmelt.