The Utility of a Thermal-based Two-Source Energy Balance Model for Estimating Surface Energy Fluxes over a Snow-dominated Landscape

A thermal-based two- source energy balance (TSEB) model is modified to estimate surface energy fluxes over snow-dominated surfaces (TSEBs). Field measurements at two sites in a sagebrush and aspen forest ecosystem during the winter are used to evaluate the utility of TSEBs. Modifications include development of routines to account for surface snow melt energy flux and snow masking of vegetation. The surface is treated as a composite of snow and vegetation elements with different temperatures, fluxes, and atmospheric coupling. This provides a single model formulation that can be applied to a wide range of snow-canopy cover conditions. Directional composite radiometric temperature and fractional vegetation cover are diagnostic variables, which allow inverse application of this energy balance modeling framework for interpretation of remote sensing data across a wide range of spatial scales. Comparisons between modeled and measured surface energy fluxes of net radiation and turbulent heat showed good agreement at both sites with the model capturing the evolution of surface energy fluxes above aspen and sagebrush canopies during active melt periods. The model also computed upward sensible heat fluxes during daytime (due to solar heating of vegetation limbs and branches) which was greater than the downward sensible heat fluxes for the snow component. This result is consistent with current and previous field observations showing upward sensible heat fluxes during the melt season in mixed snow-plant canopy systems.