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| Titel |
Aerosol effects on clouds and precipitation during the 1997 smoke episode in Indonesia |
| VerfasserIn |
H.-F. Graf, J. Yang, T. M. Wagner |
| 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. 2 ; Nr. 9, no. 2 (2009-01-29), S.743-756 |
| Datensatznummer |
250006754
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| Publikation (Nr.) |
 copernicus.org/acp-9-743-2009.pdf |
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| Zusammenfassung |
| In 1997/1998 a severe smoke episode due to extensive biomass burning,
especially of peat, was observed over Indonesia. September 1997 was the
month with the highest aerosol burden. This month was simulated using the
limited area model REMOTE driven at its lateral boundaries by ERA40
reanalysis data. REMOTE was extended by a new convective cloud
parameterization mimicking individual clouds competing for instability
energy. This allows for the interaction of aerosols, convective clouds and
precipitation. Results show that in the monthly mean convective
precipitation is diminished at nearly all places with high aerosol loading,
but at some areas with high background humidity precipitation from
large-scale clouds may over-compensate the loss in convective rainfall. The
simulations revealed that both large-scale and convective clouds'
microphysics are influenced by aerosols. Since aerosols are washed and
rained out by rainfall, high aerosol concentrations can only persist at low
rainfall rates. Hence, aerosol concentrations are not independent of the
rainfall amount and in the mean the maximum absolute effects on rainfall
from large scale clouds are found at intermediate aerosol concentrations.
The reason for this behavior is that at high aerosol concentrations rainfall
rates are small and consequently also the anomalies are small. For
large-scale as well as for convective rain negative and positive anomalies
are found for all aerosol concentrations. Negative anomalies dominate and
are highly statistically significant especially for convective rainfall
since part of the precipitation loss from large-scale clouds is compensated
by moisture detrained from the convective clouds. The mean precipitation
from large-scale clouds is less reduced (however still statistically
significant) than rain from convective clouds. This effect is due to
detrainment of cloud water from the less strongly raining convective clouds
and because of the generally lower absolute amounts of rainfall from
large-scale clouds. With increasing aerosol load both, convective and large
scale clouds produce less rain. At very few individual time steps cases were
found when polluted convective clouds produced intensified rainfall via
mixed phase microphysics. However, these cases are not unequivocal and
opposite results were also simulated, indicating that other than
aerosol-microphysics effects have important impact on the results. Overall,
the introduction of the new cumulus parameterization and aerosol-cloud
interaction reduced some of the original REMOTE biases of precipitation
patterns and total amount. |
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