Evaluating Modeled Snow-Atmosphere Coupling for Different Atmospheric and Physiographic Conditions

Improving modeled snow-atmosphere interactions should lead to better atmospheric and hydrologic predictions. However, due to model uncertainties and limited co-located snow, radiation and flux measurements, related snow-atmosphere model parameterizations and schemes have been typically evaluated at only a few observation sites, reflecting a limited range of realistic conditions with which snow-atmosphere exchanges can occur. For this study, we evaluate a land surface model (LSM) with a simplified 1-layer snow physics scheme and its ability to capture realistic snow-atmospheric interactions under different atmospheric and physiographic (e.g., topographic, vegetated) conditions. The model used is the latest Noah Unified LSM, version 3.1, and is forced with and compared to co-located in-situ meteorological data and snow and flux-related observations, respectively, from different sites within the Colorado region. These sites include tower observations from the Cold Land Processes Experiment (CLPX), Fluxes over Snow Surfaces (FLOSS) and Niwot Ridge, representing a range of environments which can influence snowpack evolution and snow-atmosphere exchanges differently (e.g., forest versus grassland, deep versus shallow snow, alpine versus sub-alpine, etc.). Of the important snow-atmospheric processes, we focus mainly on the partitioning of surface layer turbulent energy fluxes due to changes in atmospheric and snowpack conditions, but also on how these fluxes contribute to snowmelt and sublimation processes. Modeled and observed turbulent fluxes with snow present are compared for different calm and windy atmospheric conditions in both daytime and nighttime cases. For daytime cases, snow albedo and soil moisture effects on the fluxes will be also presented. Finally for the nighttime case, evaluation of the modeled snow-atmosphere interactions under stable boundary layer conditions will be highlighted.