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| Titel |
The relationship between aerosol and cloud drop number concentrations in a global aerosol microphysics model |
| VerfasserIn |
K. J. Pringle, K. S. Carslaw, D. V. Spracklen, G. M. Mann, M. P. Chipperfield |
| 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 ; 9, no. 12 ; Nr. 9, no. 12 (2009-06-22), S.4131-4144 |
| Datensatznummer |
250007440
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| Publikation (Nr.) |
 copernicus.org/acp-9-4131-2009.pdf |
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| Zusammenfassung |
| Empirical relationships that link cloud droplet number (CDN) to aerosol number
or mass are commonly used to calculate global fields of CDN for climate forcing
assessments. In this work we use a sectional global model of sulfate and sea-salt
aerosol coupled to a mechanistic aerosol activation scheme to explore the
limitations of this approach. We find that a given aerosol number concentration
produces a wide range of CDN concentrations due to variations in the shape of the
aerosol size distribution. On a global scale, the dependence of CDN on the size
distribution results in regional biases in predicted CDN (for a given aerosol
number). Empirical relationships between aerosol number and CDN are often
derived from regional data but applied to the entire globe. In an analogous
process, we derive regional "correlation-relations" between aerosol number
and CDN and apply these regional relations to calculations of CDN on the global
scale. The global mean percentage error in CDN caused by using regionally
derived CDN-aerosol relations is 20 to 26%, which is about half the global
mean percentage change in CDN caused by doubling the updraft velocity. However,
the error is as much as 25–75% in the Southern Ocean, the Arctic and regions
of persistent stratocumulus when an aerosol-CDN correlation relation from the
North Atlantic is used. These regions produce much higher CDN concentrations
(for a given aerosol number) than predicted by the globally uniform empirical
relations. CDN-aerosol number relations from different regions also show very
different sensitivity to changing aerosol. The magnitude of the rate of change
of CDN with particle number, a measure of the aerosol efficacy, varies by a
factor 4. CDN in cloud processed regions of persistent stratocumulus is
particularly sensitive to changing aerosol number. It is therefore likely
that the indirect effect will be underestimated in these important regions. |
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