Simulating black carbon and dust in snow and their climatic impact over Eurasia

Current models still have large uncertainties in estimating the impacts of light absorbing aerosols on climate. Light absorbing aerosols can affect climate through radiative effects in both atmosphere and snowpack (hereafter atmospheric-effect and snow-effect, respectively). Both effects, to some extent, have been investigated in previous studies, but few have compared the two effects and their interaction with climate. In addition, most previous studies used models with relatively coarse spatial resolutions (1~2 degrees) that may not be able to resolve climate extremes and mountain snowpack. In this study, a state-of-the-art regional model, WRF-Chem, is coupled with the SNICAR model that includes a sophisticated representation of snow metamorphism processes for climate study. The coupled model is configured at a relatively high spatial resolution (0.25 degree) to simulate black carbon (BC) and dust concentrations in snow and their climatic impact over Eurasia for 2006-2010. The simulations are evaluated with various observations including some extensive field measurements over North China. In general, the model simulated spatial variability of BC and dust mass concentrations in the top snow layer (hereafter BCS and DSTS, respectively) are consistent with observations to within the uncertainty ranges of observations. BCS and DSTS introduce similar radiative warming in the snowpack, which is comparable to the magnitude of surface radiative cooling due to BC and dust in the atmosphere. The impact of BC and dust in the snowpack and in the atmosphere on the variability of regional hydrological cycle and temperature is characterized separately by sequentially "disconnecting" specific BC and dust forcing in the atmosphere and in the snowpack. This study represents an effort in using a regional modeling framework with a relatively high resolution to simulate BC and dust in snowpack and their climatic impact.