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| Titel |
Are simulated aerosol-induced effects on deep convective clouds strongly dependent on saturation adjustment? |
| VerfasserIn |
Z. J. Lebo, H. Morrison, J. H. Seinfeld |
| 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 ; 12, no. 20 ; Nr. 12, no. 20 (2012-10-30), S.9941-9964 |
| Datensatznummer |
250011545
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| Publikation (Nr.) |
 copernicus.org/acp-12-9941-2012.pdf |
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| Zusammenfassung |
| Three configurations of a bulk microphysics scheme in conjunction with a
detailed bin scheme are implemented in the Weather Research and Forecasting
(WRF) model to specifically address the role of the saturation adjustment
assumption (i.e., condensing/evaporating the surplus/deficit water vapor
relative to saturation in one time step) on aerosol-induced invigoration of
deep convective clouds. The bulk model configurations are designed to treat
cloud droplet condensation/evaporation using either saturation adjustment, as
employed in most bulk models, or an explicit representation of
supersaturation over a time step, as used in bin models. Results demonstrate
that the use of saturation adjustment artificially enhances condensation and
latent heating at low levels and limits the potential for an increase in
aerosol concentration to increase buoyancy at mid to upper levels. This leads
to a small weakening of the time- and domain-averaged convective mass flux
(~-3%) in polluted compared to clean conditions. In contrast, the bin
model and bulk scheme with explicit prediction of supersaturation simulate an
increase in latent heating aloft and the convective updraft mass flux is
weakly invigorated (~5%). The bin model also produces a large
increase in domain-mean cumulative surface precipitation in polluted
conditions (~18%), while all of the bulk model configurations
simulate little change in precipitation. Finally, it is shown that the cold
pool weakens substantially with increased aerosol loading when saturation
adjustment is applied, which acts to reduce the low-level convergence and
weaken the convective dynamics. With an explicit treatment of supersaturation
in the bulk and bin models there is little change in cold pool strength, so
that the convective response to polluted conditions is influenced more by
changes in latent heating aloft. It is concluded that the use of saturation
adjustment can explain differences in the response of cold pool evolution and
convective dynamics with aerosol loading simulated by the bulk and bin
models, but cannot explain large differences in the response of surface
precipitation between these models. |
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