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| Titel |
Impact of cloud-borne aerosol representation on aerosol direct and indirect effects |
| VerfasserIn |
S. J. Ghan, R. C. Easter |
| 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 ; 6, no. 12 ; Nr. 6, no. 12 (2006-09-21), S.4163-4174 |
| Datensatznummer |
250004113
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| Publikation (Nr.) |
 copernicus.org/acp-6-4163-2006.pdf |
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| Zusammenfassung |
| Aerosol particles attached to cloud droplets are much more likely to be
removed from the atmosphere and are much less efficient at scattering
sunlight than if unattached. Models used to estimate direct and indirect
effects of aerosols employ a variety of representations of such cloud-borne
particles. Here we use a global aerosol model with a relatively complete
treatment of cloud-borne particles to estimate the sensitivity of simulated
aerosol, cloud and radiation fields to various approximations to the
representation of cloud-borne particles. We find that neglecting transport
of cloud-borne particles introduces little error, but that diagnosing
cloud-borne particles produces global mean biases of 20% and local errors
of up to 40% for aerosol, droplet number, and direct and indirect
radiative forcing. Aerosol number, aerosol optical depth and droplet number
are significantly underestimated in regions and seasons where and when wet
removal is primarily by stratiform rather than convective clouds (polar
regions during winter), but direct and indirect effects are less biased
because of the limited sunlight there and then. A treatment that predicts
the total mass concentration of cloud-borne particles for each mode yields
smaller errors and runs 20% faster than the complete treatment. The
errors are much smaller than current estimates of uncertainty in direct and
indirect effects of aerosols, which suggests that the treatment of
cloud-borne aerosol is not a significant source of uncertainty in estimates
of direct and indirect effects. |
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