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| Titel |
Biases in modeled surface snow BC mixing ratios in prescribed-aerosol climate model runs |
| VerfasserIn |
S. J. Doherty, C. M. Bitz, M. G. Flanner |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 21 ; Nr. 14, no. 21 (2014-11-07), S.11697-11709 |
| Datensatznummer |
250119143
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| Publikation (Nr.) |
 copernicus.org/acp-14-11697-2014.pdf |
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| Zusammenfassung |
| 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. |
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