UCLA Department of Atmospheric and Oceanic Sciences
“Investigation of Impact of Aerosols in Snow on Regional Hydrology and Climate Using Improved Snow Scheme in a Regional Climate Model”
With an observed increase in recent decades in aerosol deposition (dust, black carbon) onto mountain snowpacks around the world, which affects snow albedo, snowmelt, hydrologic cycle, and climate, the impact of these light-absorbing impurities in snow on a regional scale is of great interest to society. Most models do not include snow aging and interactive snow-aerosol radiative transfer processes, both of which are necessary to capture the full snow-albedo feedbacks in a realistic manner. Furthermore, most modeling studies use coarse resolution GCMs, which cannot adequately resolve complex mountainous terrain and associated precipitation/snow processes. In this work, we develop a more physically-based model by improving snow processes in SSiB land surface model that is coupled with WRF regional climate model (RCM). This is accomplished by introducing SNICAR model (Flanner & Zender, 2006) into WRF/SSiB, which simulates snow aging and vertically-resolved radiative transfer in the snowpack. We also further modify WRF/SSiB to account for physical presence of impurities in snow, their movement within the pack, and removal by meltwater. Here, we present model development technique, validation with in situ observations, and preliminary results from the RCM simulations. We find that by including snow/aerosol interactions, the model is able to realistically simulate observed surface water and energy balances. Over western U.S., realistic aerosol deposition in snow induces a springtime average radiative forcing of 33W/m2, a regional surface warming of 1.46°K, and a snowpack reduction of 40mm. The preliminary RCM results also suggest this aerosols-in-snow radiative forcing has an effect on regional land-atmosphere interactions and atmospheric circulation, such as the North American monsoon.