Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Journal topic

Journal metrics

Journal metrics

  • IF value: 5.668 IF 5.668
  • IF 5-year value: 6.201 IF 5-year
    6.201
  • CiteScore value: 6.13 CiteScore
    6.13
  • SNIP value: 1.633 SNIP 1.633
  • IPP value: 5.91 IPP 5.91
  • SJR value: 2.938 SJR 2.938
  • Scimago H <br class='hide-on-tablet hide-on-mobile'>index value: 174 Scimago H
    index 174
  • h5-index value: 87 h5-index 87
Volume 14, issue 21
Atmos. Chem. Phys., 14, 11697-11709, 2014
https://doi.org/10.5194/acp-14-11697-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 14, 11697-11709, 2014
https://doi.org/10.5194/acp-14-11697-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 07 Nov 2014

Research article | 07 Nov 2014

Biases in modeled surface snow BC mixing ratios in prescribed-aerosol climate model runs

S. J. Doherty1, C. M. Bitz2, and M. G. Flanner3 S. J. Doherty et al.
  • 1Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, 3737 Brooklyn Ave. NE, Seattle, WA 98195, USA
  • 2Department of Atmospheric Sciences, 408 ATG, Box 351640, University of Washington, Seattle, WA 98195, USA
  • 3Dept. of Atmospheric, Oceanic and Space Sciences, University of Michigan, 2455 Hayward St., Ann Arbor, MI 48109-2143, USA

Abstract. Black carbon (BC) in snow lowers its albedo, increasing the absorption of sunlight, leading to positive radiative forcing, climate warming and earlier snowmelt. A series of recent studies have used prescribed-aerosol deposition flux fields in climate model runs to assess the forcing by black carbon in snow. In these studies, the prescribed mass deposition flux of BC to surface snow is decoupled from the mass deposition flux of snow water to the surface. Here we compare prognostic- and prescribed-aerosol runs and use a series of offline calculations to show that the prescribed-aerosol approach results, on average, in a factor of about 1.5–2.5 high bias in annual-mean surface snow BC mixing ratios in three key regions for snow albedo forcing by BC: Greenland, Eurasia and North America. These biases will propagate directly to positive biases in snow and surface albedo reduction by BC. The bias is shown be due to coupling snowfall that varies on meteorological timescales (daily or shorter) with prescribed BC mass deposition fluxes that are more temporally and spatially smooth. The result is physically non-realistic mixing ratios of BC in surface snow. We suggest that an alternative approach would be to prescribe BC mass mixing ratios in snowfall, rather than BC mass fluxes, and we show that this produces more physically realistic BC mixing ratios in snowfall and in the surface snow layer.

Publications Copernicus
Download
Short summary
Black carbon in snow lowers its albedo, increasing the absorption of sunlight, leading to positive radiative forcing, climate warming and earlier snow-melt. A series of recent studies have used prescribed rates of black carbon deposition to snow to assess the climate effects of black carbon in snow. Here we show that the use of prescribed deposition fluxes in these model studies leads to high biases in snow BC concentrations, caused by the decoupling of BC and snow deposition to the surface.
Black carbon in snow lowers its albedo, increasing the absorption of sunlight, leading to...
Citation
Share