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| Titel |
Cloud-system resolving model simulations of aerosol indirect effects on tropical deep convection and its thermodynamic environment |
| VerfasserIn |
H. Morrison, W. W. Grabowski |
| 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 ; 11, no. 20 ; Nr. 11, no. 20 (2011-10-24), S.10503-10523 |
| Datensatznummer |
250010140
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| Publikation (Nr.) |
 copernicus.org/acp-11-10503-2011.pdf |
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| Zusammenfassung |
| This paper presents results from 240-member ensemble
simulations of aerosol indirect effects on tropical deep convection and its
thermodynamic environment. Simulations using a two-dimensional cloud-system
resolving model are run with pristine, polluted, or highly polluted aerosol
conditions and large-scale forcing from a 6-day period of active monsoon
conditions during the 2006 Tropical Warm Pool – International Cloud
Experiment (TWP-ICE). Domain-mean surface precipitation is insensitive to
aerosols primarily because the large-scale forcing is prescribed and
dominates the water and static energy budgets. The spread of the
top-of-atmosphere (TOA) shortwave and longwave radiative fluxes among
different ensemble members for the same aerosol loading is surprisingly
large, exceeding 25 W m−2 even when averaged over the 6-day period.
This variability is caused by random fluctuations in the strength and timing
of individual deep convective events. The ensemble approach demonstrates a
small weakening of convection averaged over the 6-day period in the polluted
simulations compared to pristine. Despite this weakening, the cloud top
heights and anvil ice mixing ratios are higher in polluted conditions. This
occurs because of the larger concentrations of cloud droplets that freeze,
leading directly to higher ice particle concentrations, smaller ice particle
sizes, and smaller fall velocities compared to simulations with pristine
aerosols. Weaker convection in polluted conditions is a direct result of the
changes in anvil ice characteristics and subsequent upper-tropospheric
radiative heating and weaker tropospheric destabilization. Such a conclusion
offers a different interpretation of recent satellite observations of
tropical deep convection in pristine and polluted environments compared to
the hypothesis of aerosol-induced convective invigoration. Sensitivity tests
using the ensemble approach with modified microphysical parameters or domain
configuration (horizontal gridlength, domain size) produce results that are
similar to baseline, although there are quantitative differences in
estimates of aerosol impacts on TOA radiative fluxes. |
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