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| Titel |
The role of the particle size distribution in assessing aerosol composition effects on simulated droplet activation |
| VerfasserIn |
D. S. Ward, T. Eidhammer, W. R. Cotton, S. M. Kreidenweis |
| 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. 12 ; Nr. 10, no. 12 (2010-06-21), S.5435-5447 |
| Datensatznummer |
250008563
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| Publikation (Nr.) |
 copernicus.org/acp-10-5435-2010.pdf |
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| Zusammenfassung |
| Variations in the chemical composition of atmospheric aerosols alter their
hygroscopicity and can lead to changes in the cloud-active fraction of the
aerosols, or cloud condensation nuclei (CCN) number concentration. To
investigate the importance of this effect under different atmospheric
conditions, cloud droplet formation was simulated with a Lagrangian parcel
model. Initial values of updraft speed and temperature were systematically
varied along with aerosol number concentration, size and hygroscopicity
(represented by the hygroscopicity parameter, κ). A previous study classifies
the sensitivity of CCN activity to compositional changes based on the
supersaturation reached in the parcel model. We found that these
classifications could not be generalized to a range of aerosol size
distribution median radii. Instead, variations in sensitivity with size
depend on the location of the dry critical radius for droplet activation
relative to the size distribution median radius. The parcel model output was
used to construct droplet activation lookup tables based on κ that
were implemented in the Regional Atmospheric Modeling System (RAMS)
microphysical scheme. As a first application of this system, aerosol
hygroscopicity and size were varied in a series of RAMS mesoscale
simulations designed to investigate the sensitivity of a mixed-phase
orographic cloud case to the parameter variations. Observations from a
recent field campaign in northwestern Colorado provided the basis for the
aerosol field initializations. Model results show moderate sensitivity in
the distribution of total case precipitation to extreme changes in κ, and
minimal sensitivity to observed changes in estimated κ. The impact of varying
aerosol hygroscopicity diminished with increasing median radius, as expected
from the parcel model results. The conclusions drawn from these simulations
could simplify similar research in other cloud regimes by defining the need,
or lack of need, for detailed knowledge of aerosol composition. |
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