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| Titel |
Examination of aerosol distributions and radiative effects over the Bay of Bengal and the Arabian Sea region during ICARB using satellite data and a general circulation model |
| VerfasserIn |
R. Cherian, C. Venkataraman, S. Ramachandran, J. Quaas, S. Kedia |
| 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. 3 ; Nr. 12, no. 3 (2012-02-01), S.1287-1305 |
| Datensatznummer |
250010630
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| Publikation (Nr.) |
 copernicus.org/acp-12-1287-2012.pdf |
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| Zusammenfassung |
| In this paper we analyse aerosol loading and its direct radiative effects
over the Bay of Bengal (BoB) and Arabian Sea (AS) regions for the Integrated
Campaign on Aerosols, gases and Radiation Budget (ICARB) undertaken during
2006, using satellite data from the MODerate Resolution Imaging
Spectroradiometer (MODIS) on board the Terra and Aqua satellites, the
Aerosol Index from the Ozone Monitoring Instrument (OMI) on board the Aura
satellite, and the European-Community Hamburg (ECHAM5.5) general circulation
model extended by Hamburg Aerosol Module (HAM). By statistically comparing
with large-scale satellite data sets, we firstly show that the aerosol
properties measured during the ship-based ICARB campaign and simulated by
the model are representative for the BoB and AS regions and the pre-monsoon
season. In a second step, the modelled aerosol distributions were evaluated
by a comparison with the measurements from the ship-based sunphotometer, and
the satellite retrievals during ICARB. It is found that the model broadly
reproduces the observed spatial and temporal variability in aerosol optical
depth (AOD) over BoB and AS regions. However, AOD was systematically
underestimated during high-pollution episodes, especially in the BoB leg. We
show that this underprediction of AOD is mostly because of the deficiencies
in the coarse mode, where the model shows that dust is the dominant
component. The analysis of dust AOD along with the OMI Aerosol Index
indicate that missing dust transport that results from too low dust emission
fluxes over the Thar Desert region in the model caused this deficiency.
Thirdly, we analysed the spatio-temporal variability of AOD comparing the
ship-based observations to the large-scale satellite observations and
simulations. It was found that most of the variability along the track was
from geographical patterns, with a minor influence by single events. Aerosol
fields were homogeneous enough to yield a good statistical agreement between
satellite data at a 1° spatial, but only twice-daily temporal
resolution, and the ship-based sunphotometer data at a much finer spatial,
but daily-average temporal resolution. Examination of the satellite data
further showed that the year 2006 is representative for the five-year period
for which satellite data were available. Finally, we estimated the clear-sky
solar direct aerosol radiative forcing (DARF). We found that the cruise
represents well the regional-seasonal mean forcings. Constraining simulated
forcings using the observed AOD distributions yields a robust estimate of
regional-seasonal mean DARF of −8.6, −21.4 and +12.9 W m−2 at the top
of the atmosphere (TOA), at the surface (SUR) and in the atmosphere (ATM),
respectively, for the BoB region, and over the AS, of, −6.8, −12.8, and +6 W m−2 at TOA, SUR, and ATM, respectively. |
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