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| Titel |
Explicit simulations of aerosol physics in a cloud-resolving model: a sensitivity study based on an observed convective cloud |
| VerfasserIn |
A. M. L. Ekman, C. Wang, J. Wilson, J. Ström |
| 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 ; 4, no. 3 ; Nr. 4, no. 3 (2004-05-18), S.773-791 |
| Datensatznummer |
250001716
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| Publikation (Nr.) |
 copernicus.org/acp-4-773-2004.pdf |
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| Zusammenfassung |
| The role of convection in introducing aerosols and promoting the formation
of new particles to the upper troposphere has been examined using a
cloud-resolving model coupled with an interactive explicit aerosol module. A
baseline simulation suggests good agreement in the upper troposphere between
modeled and observed results including concentrations of aerosols in
different size ranges, mole fractions of key chemical species, and
concentrations of ice particles. In addition, a set of 34 sensitivity
simulations has been carried out to investigate the sensitivity of modeled
results to the treatment of various aerosol physical and chemical processes
in the model. The size distribution of aerosols is proved to be an important
factor in determining the aerosols' fate within the convective cloud.
Nucleation mode aerosols (here defined by 0≤d≤5.84 nm) are
quickly transferred to the larger modes as they grow through coagulation of
aerosols and condensation of H2SO4. Accumulation mode aerosols
(here defined by d≥31.0 nm) are almost completely removed by
nucleation (activation of cloud droplets) and impact scavenging. However, a
substantial part (up to 10% of the boundary layer concentration) of the
Aitken mode aerosol population (here defined by 5.84 nm≤d≤31.0 nm)
reaches the top of the cloud and the free troposphere. These particles
may continually survive in the upper troposphere, or over time form ice
crystals, both that could impact on the atmospheric radiative budget. The
sensitivity simulations performed indicate that critical processes in the
model causing a substantial change in the upper tropospheric number
concentration of Aitken mode aerosols are coagulation of aerosols,
condensation of H2SO4, nucleation scavenging, nucleation of
aerosols and the transfer of aerosol mass and number between different
aerosol bins. In particular, for aerosols in the Aitken mode to grow to CCN
size, coagulation of aerosols appears to be more important than condensation
of H2SO4. Less important processes are dry deposition, impact
scavenging and the initial vertical distribution and concentration of
aerosols. It is interesting to note that in order to sustain a vigorous
storm cloud, the supply of CCN must be continuous over a considerably long
time period of the simulation. Hence, the treatment of the growth of
particles is in general much more important than the initial aerosol
concentration itself. |
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