New Features and Enhancements in Community Land Model (CLM5) Snow Albedo Modeling: Description, Sensitivity, and Evaluation

We enhance the Community Land Model (CLM) snow albedo modeling by implementing several new features with more realistic and physical representations of snow-aerosol-radiation interactions. Specifically, we incorporate the following model enhancements: (a) updating ice and aerosol optical properties with more realistic and accurate data sets, (b) adding multiple dust types, (c) adding multiple surface downward solar spectra to account for different atmospheric conditions, (d) incorporating a more accurate adding-doubling radiative transfer solver, (e) adding nonspherical snow grain representations, (f) adding black carbon-snow and dust-snow internal mixing representations, and (g) adding a hyperspectral (480-band vs. the default 5-band) modeling capability. These model features/enhancements are included as new CLM physics/namelist options, which allows for quantification of model sensitivity to snow albedo processes and for multi-physics model ensemble analyses for uncertainty assessment. The model updates have been included in the latest released CLM version. Sensitivity analyses reveal strong impacts of using the new adding-doubling solver, nonspherical snow grains, aerosol-snow internal mixing, updated aerosol optics, and different dust types. These enhanced snow albedo representations improve the CLM simulated global snowpack evolution and land surface conditions, with reduced biases in simulated snow surface albedo, snow cover, snow water equivalent, snow depth, and surface (2-m) air temperature over many mid-latitude mountainous regions and seasonal snowpacks but degraded performance in some northern high-latitude regions. Snow albedo plays a critical role in the Earth system, affecting land surface energy and water balance and also serving as an important land process that feeds back to the atmosphere. Several recent studies have identified new or improved physical representations of snow albedo processes. In this study, we leverage recent advances in snow albedo modeling to implement a number of relevant new features into the widely used Community Land Model (CLM), which is the land component of the Community Earth System Model (CESM). Specifically, we improve the ice and aerosol optical properties, the treatment of dust types and downward sunlight energy distribution at different wavelength bands, the albedo computation algorithm, and the representations of snow grain shape and how aerosol is mixed with snow grains. These model updates have been included in the latest released CLM version. Overall, the enhanced snow albedo representations improve the simulated snowpack evolution and related land surface conditions in many parts of the globe. We enhance CLM5 snow albedo modeling by including more realistic and physical representations of snow-aerosol-radiation interactions The new adding-doubling solver, nonspherical snow grains, aerosol-snow internal mixing, and updated aerosol optics show strong impacts The enhanced snow albedo representation improves the CLM simulated snowpack evolution and land surface conditions in many global regions