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| Titel |
Influences of in-cloud aerosol scavenging parameterizations on aerosol concentrations and wet deposition in ECHAM5-HAM |
| VerfasserIn |
B. Croft, U. Lohmann, R. V. Martin, P. Stier, S. Wurzler, J. Feichter, C. Hoose, U. Heikkilä, A. Donkelaar, S. Ferrachat |
| 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 ; 10, no. 4 ; Nr. 10, no. 4 (2010-02-15), S.1511-1543 |
| Datensatznummer |
250008100
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| Publikation (Nr.) |
 copernicus.org/acp-10-1511-2010.pdf |
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| Zusammenfassung |
| A diagnostic cloud nucleation scavenging scheme, which determines stratiform
cloud scavenging ratios for both aerosol mass and number
distributions, based on cloud droplet, and ice crystal number
concentrations, is introduced into the ECHAM5-HAM global climate
model. This scheme is coupled with a size-dependent in-cloud impaction
scavenging parameterization for both cloud droplet-aerosol, and ice
crystal-aerosol collisions. The aerosol mass scavenged in stratiform clouds is
found to be primarily (>90%) scavenged by cloud nucleation processes for
all aerosol species, except for dust (50%). The aerosol number scavenged is
primarily (>90%) attributed to impaction. 99% of this impaction scavenging
occurs in clouds with temperatures less than 273 K. Sensitivity studies are
presented, which compare aerosol concentrations, burdens, and deposition for a variety of
in-cloud scavenging approaches: prescribed fractions, a more computationally
expensive prognostic aerosol cloud processing treatment, and the new diagnostic
scheme, also with modified assumptions about in-cloud impaction and nucleation scavenging.
Our results show that while uncertainties in the representation of in-cloud
scavenging processes can lead to differences in the range of 20–30% for the
predicted annual, global mean aerosol mass burdens, and near to 50% for
accumulation mode aerosol number burden, the differences in predicted aerosol
mass concentrations can be up to one order of magnitude, particularly for
regions of the middle troposphere with temperatures below 273 K where mixed
and ice phase clouds exist. Different parameterizations for impaction scavenging
changed the predicted global, annual mean number removal attributed to ice clouds
by seven-fold, and the global, annual dust mass removal attributed to impaction
by two orders of magnitude. Closer agreement with observations of black carbon
profiles from aircraft (increases near to one order of magnitude for mixed
phase clouds), mid-troposphere 210Pb vertical profiles, and the
geographic distribution of aerosol optical depth is found for the new diagnostic
scavenging scheme compared to the prescribed scavenging fraction scheme of the standard ECHAM5-HAM. The
diagnostic and prognostic schemes represent the variability of scavenged fractions
particularly for submicron size aerosols, and for mixed and ice phase clouds,
and are recommended in preference to the prescribed scavenging fractions method. |
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