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| Titel |
Aerosol–climate interactions in the Norwegian Earth System Model – NorESM1-M |
| VerfasserIn |
A. Kirkevåg, T. Iversen, Ø. Seland, C. Hoose, J. E. Kristjánsson, H. Struthers, A. M. L. Ekman, S. Ghan, J. Griesfeller, E. D. Nilsson, M. Schulz |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 6, no. 1 ; Nr. 6, no. 1 (2013-02-08), S.207-244 |
| Datensatznummer |
250017367
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| Publikation (Nr.) |
 copernicus.org/gmd-6-207-2013.pdf |
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| Zusammenfassung |
The objective of this study is to document and evaluate recent changes and
updates to the module for aerosols and aerosol–cloud–radiation interactions
in the atmospheric module CAM4-Oslo of the core version of
the Norwegian Earth System Model (NorESM), NorESM1-M.
Particular attention is paid to the role of natural organics, sea
salt, and mineral dust in determining the gross aerosol properties as well
as the anthropogenic contribution to these properties and the associated
direct and indirect radiative forcing.
The aerosol module is extended from earlier versions that have been
published, and includes life-cycling of sea salt, mineral dust, particulate
sulphate, black carbon, and primary and secondary organics. The impacts of
most of the numerous changes since previous versions are thoroughly explored
by sensitivity experiments. The most important changes are: modified
prognostic sea salt emissions; updated treatment of precipitation scavenging
and gravitational settling; inclusion of biogenic primary organics and
methane sulphonic acid (MSA) from oceans; almost doubled production of
land-based biogenic secondary organic aerosols (SOA); and increased ratio of
organic matter to organic carbon (OM/OC) for biomass burning aerosols from
1.4 to 2.6.
Compared with in situ measurements and remotely sensed data, the new
treatments of sea salt and dust aerosols give smaller biases in near-surface
mass concentrations and aerosol optical depth than in the earlier model
version. The model biases for mass concentrations are approximately
unchanged for sulphate and BC. The enhanced levels of modeled OM yield
improved overall statistics, even though OM is still underestimated in
Europe and overestimated in North America.
The global anthropogenic aerosol
direct radiative forcing (DRF) at the top of the atmosphere has
changed from a small positive value to −0.08 W m−2 in CAM4-Oslo. The
sensitivity tests suggest that this change can be attributed to the new
treatment of biomass burning aerosols and gravitational settling. Although it
has not been a goal in this study, the new DRF estimate is closer both to the
median model estimate from the AeroCom intercomparison and the best estimate
in IPCC AR4. Estimated DRF at the ground surface has increased by
ca. 60%, to −1.89 W m−2. We show that this can be explained by
new emission data and omitted mixing of constituents between updrafts and
downdrafts in convective clouds.
The increased abundance of natural OM and the introduction of a cloud droplet
spectral dispersion formulation are the most important contributions to a
considerably decreased estimate of the indirect radiative forcing (IndRF).
The IndRF is also found to be sensitive to assumptions about the coating of
insoluble aerosols by sulphate and OM. The IndRF of −1.2 W m−2,
which is closer to the IPCC AR4 estimates than the previous estimate of
−1.9 W m−2, has thus been obtained without imposing unrealistic
artificial lower bounds on cloud droplet number concentrations. |
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