Abstract
Abstract. Light-absorbing particles (LAPs), mainly dust and black carbon, can significantly impact snowmelt and regional water availability over high-mountain Asia (HMA). In this study, for the first time, online aerosol–snow interactions are enabled and a fully coupled chemistry Weather Research and Forecasting (WRF-Chem) regional model is used to simulate LAP-induced radiative forcing on snow surfaces in HMA at relatively high spatial resolution (12 km, WRF-HR) compared with previous studies. Simulated macro- and microphysical properties of the snowpack and LAP-induced snow darkening are evaluated against new spatially and temporally complete datasets of snow-covered area, grain size, and impurity-induced albedo reduction over HMA. A WRF-Chem quasi-global simulation with the same configuration as WRF-HR but a coarser spatial resolution (1∘, WRF-CR) is also used to illustrate the impact of spatial resolution on simulations of snow properties and aerosol distribution over HMA. Due to a more realistic representation of terrain slopes over HMA, the higher-resolution model (WRF-HR) shows significantly better performance in simulating snow area cover, duration of snow cover, snow albedo and snow grain size over HMA, as well as an evidently better atmospheric aerosol loading and mean LAP concentration in snow. However, the differences in albedo reduction from model and satellite retrievals is large during winter due to associated overestimation in simulated snow fraction. It is noteworthy that Himalayan snow cover has high magnitudes of LAP-induced snow albedo reduction (4 %–8 %) in pre-monsoon seasons (both from WRF-HR and satellite estimates), which induces a snow-mediated radiative forcing of ∼30–50 W m−2. As a result, the Himalayas (specifically the western Himalayas) hold the most vulnerable glaciers and mountain snowpack to the LAP-induced snow darkening effect within HMA. In summary, coarse spatial resolution and absence of snow–aerosol interactions over the Himalayan cryosphere will result in significant underestimation of aerosol effects on snow melting and regional hydroclimate.
Highlights
Light-absorbing aerosol particles (LAPs; airborne dust and black carbon (BC) specks), can impact regional water availability over Asia in three ways
The main objective of this study is to evaluate the skill of the high-resolution WRF-Chem model in simulating properties of snowpack, aerosol distribution, LAP in snow and LAP-induced snow darkening over high-mountain Asia (HMA) using spatially and temporally complete (STC) remotely sensed snow surface properties (SSPs) from MODIS (Dozier et al, 2008; Rittger et al, 2016)
The largest values of region-averaged annual mean fractional snow-covered area (fSCA) within HMA are observed in both the satellite retrievals and the model runs over the Karakoram region followed by the Pamirs, Himalayas and Hindu Kush in the HMA region (Fig. 2a and b)
Summary
Light-absorbing aerosol particles (LAPs; airborne dust and black carbon (BC) specks), can impact regional water availability over Asia in three ways. LAPs can directly interact with incoming solar radiation and induce thermodynamical modifications to synoptic-scale circulations (Hansen et al, 1997; Ramanathan et al, 2001; Bond et al, 2013; Lau et al, 2006; Bollasina et al, 2011; Li et al, 2016). Acting as cloud condensation nuclei, changes in concentrations of these particles can lead to microphysical modification of cloud systems and precipitations (Fan et al, 2016; Li et al, 2016; Qian et al, 2009; Sarangi et al, 2017). Deposition of LAPs in the snowpack can darken the snow, reduce its surface albedo, and accelerate snow warming and melting
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