Examining the atmospheric radiative and snow-darkening effects of black carbon and dust across the Rocky Mountains of the United States using WRF-Chem
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Abstract. WRF-Chem is run to quantify the in-snow and atmospheric radiative effects of black carbon and dust (BCD, collectively) on a convective-allowing (4-km) grid for water year 2009 across a large area of the Rocky Mountains. The snow darkening effect (SDE) due to the deposition of BCD on surface snow accelerates the snowmelt by 3 to 12 millimeters during late spring and early summer, effectuating runoff increases (decreases) prior to (after) June. Meanwhile, aerosol radiation interactions (ARI) associated with BCD generally dim the surface from incoming solar energy, introducing an energy deficit at the surface and lead to snowpack preservation by 1 to 5 millimeters. Runoff alterations brought forth by BCD ARI are of opposite phase to those associated with BCD SDEs, and the BC SDE drives a majority of the surface energy and hydrological perturbations. More generally, changes in snow water equivalent (SWE) brought forth by BCD effects are due to perturbations to the surface energy budget and not initiated by changes in precipitation amount or type. It is also found that perturbations to the surface energy budget by dust ARI can differ in sign from those of BC ARI, with the former being positive across high-albedo surfaces, enhancing snow melting and changing runoff.
