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.