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| Titel |
Spatial variability of the direct radiative forcing of biomass burning aerosols and the effects of land use change in Amazonia |
| VerfasserIn |
E. T. Sena, P. Artaxo, A. L. Correia |
| 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 ; 13, no. 3 ; Nr. 13, no. 3 (2013-02-01), S.1261-1275 |
| Datensatznummer |
250017628
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| Publikation (Nr.) |
 copernicus.org/acp-13-1261-2013.pdf |
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| Zusammenfassung |
This paper addresses the Amazonian shortwave radiative budget over
cloud-free conditions after considering three aspects of deforestation:
(i) the emission of aerosols from biomass burning due to forest fires;
(ii) changes in surface albedo after deforestation; and (iii) modifications in the
column water vapour amount over deforested areas. Simultaneous Clouds and
the Earth's Radiant Energy System (CERES) shortwave fluxes and aerosol
optical depth (AOD) retrievals from the Moderate Resolution Imaging
SpectroRadiometer (MODIS) were analysed during the peak of the biomass
burning seasons (August and September) from 2000 to 2009. A
discrete-ordinate radiative transfer (DISORT) code was used to extend
instantaneous remote sensing radiative forcing assessments into 24-h
averages.
The mean direct radiative forcing of aerosols at the top of the atmosphere
(TOA) during the biomass burning season for the 10-yr studied period was
−5.6 ± 1.7 W m−2. Furthermore, the spatial distribution
of the direct radiative forcing of aerosols over Amazonia was obtained for the
biomass burning season of each year. It was observed that for high AOD
(larger than 1 at 550 nm) the maximum daily direct aerosol radiative forcing
at the TOA may be as high as −20 W m−2 locally. The surface reflectance
plays a major role in the aerosol direct radiative effect. The study of the
effects of biomass burning aerosols over different surface types shows that
the direct radiative forcing is systematically more negative over forest
than over savannah-like covered areas. Values of −15.7 ± 2.4 W m−2τ550 nm
and −9.3 ± 1.7 W m−2τ550 nm
were calculated for the mean daily aerosol forcing efficiencies
over forest and savannah-like vegetation respectively. The overall mean
annual land use change radiative forcing due to deforestation over the state
of Rondônia, Brazil, was determined as −7.3 ± 0.9 W m−2.
Biomass burning aerosols impact the radiative budget for
approximately two months per year, whereas the surface albedo impact is
observed throughout the year. Because of this difference, the estimated
impact in the Amazonian annual radiative budget due to surface albedo-change
is approximately 6 times higher than the impact due to aerosol emissions.
The influence of atmospheric water vapour content in the radiative budget
was also studied using AERONET column water vapour. It was observed that
column water vapour is on average smaller by about 0.35 cm (around 10% of
the total column water vapour) over deforested areas compared to forested
areas. Our results indicate that this drying contributes to an increase in
the shortwave radiative forcing, which varies from 0.4 W m−2 to 1.2 W m−2
depending on the column water vapour content before
deforestation.
The large radiative forcing values presented in this study point out that
deforestation could have strong implications in convection, cloud
development and the ratio of direct to diffuse radiation, which impacts
carbon uptake by the forest. |
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