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| Titel |
Microphysical and radiative effects of aerosols on warm clouds during the Amazon biomass burning season as observed by MODIS: impacts of water vapor and land cover |
| VerfasserIn |
J. E. Hoeve, L. A. Remer, M. Z. Jacobson |
| 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. 7 ; Nr. 11, no. 7 (2011-04-01), S.3021-3036 |
| Datensatznummer |
250009577
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| Publikation (Nr.) |
 copernicus.org/acp-11-3021-2011.pdf |
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| Zusammenfassung |
| Aerosol, cloud, water vapor, and temperature profile data from the Moderate
Resolution Imaging Spectroradiometer (MODIS) are utilized to examine the
impact of aerosols on clouds during the Amazonian biomass burning season in
Rondônia, Brazil. It is found that increasing background column water
vapor (CWV) throughout this transition season between the Amazon dry and wet
seasons likely exerts a strong effect on cloud properties. As a result,
proper analysis of aerosol-cloud relationships requires that data be
stratified by CWV to account better for the influence of background
meteorological variation. Many previous studies of aerosol-cloud
interactions over Amazonia have ignored the systematic changes to
meteorological factors during the transition season, leading to possible
misinterpretation of their results. Cloud fraction (CF) is shown to increase
or remain constant with aerosol optical depth (AOD), depending on the value
of CWV, whereas the relationship between cloud optical depth (COD) and AOD
is quite different. COD increases with AOD until AOD ~ 0.3, which is
assumed to be due to the first indirect (microphysical) effect. At higher
values of AOD, COD is found to decrease with increasing AOD, which may be
due to: (1) the inhibition of cloud development by absorbing aerosols
(radiative effect/semi-direct effect) and/or (2) a possible retrieval
artifact in which the measured reflectance in the visible is less than
expected from a cloud top either from the darkening of clouds through the
addition of carbonaceous biomass burning aerosols within or above clouds or
subpixel dark surface contamination in the measured cloud reflectance. If
(1) is a contributing mechanism, as we suspect, then an empirically-derived
increasing function between cloud drop number and aerosol concentration,
assumed in a majority of global climate models, is inaccurate since these
models do not include treatment of aerosol absorption in and around clouds.
The relationship between aerosols and both CWV and clouds over varying land
surface types is also analyzed. The study finds that the difference in CWV
between forested and deforested land is not correlated with aerosol loading,
supporting the assumption that temporal variation of CWV is primarily a
function of the larger-scale meteorology. However, a difference in the
response of CF to increasing AOD is observed between forested and deforested
land. This suggests that dissimilarities between other meteorological
factors, such as atmospheric stability, may have an impact on aerosol-cloud
correlations between different land cover types. |
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