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| Titel |
Temporal heterogeneity in aerosol characteristics and the resulting radiative impact at a tropical coastal station – Part 1: Microphysical and optical properties |
| VerfasserIn |
K. Krishna Moorthy, S. Suresh Babu, S. K. Satheesh |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 25, no. 11 ; Nr. 25, no. 11 (2007-11-29), S.2293-2308 |
| Datensatznummer |
250015941
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| Publikation (Nr.) |
 copernicus.org/angeo-25-2293-2007.pdf |
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| Zusammenfassung |
| In Part 1 of this two-part paper, we present the results of extensive and
collocated measurements of the columnar and near-surface (in the well mixed
region) properties of atmospheric aerosol particles at a tropical coastal
location, Trivandrum (8.55° N; 76.97° E), located close to the
southwest tip of Indian peninsula. These are used to evolve average,
climatological pictures of the optical and microphysical properties and to
delineate the distinct changes associated with the contrasting monsoon
seasons as well as the transition from one season to the other. Our
observations show a dramatic change in the columnar aerosol optical depth
(AOD) spectra, being steep during winter monsoon season (WMS, months of
December through March) and becoming quite flat during summer monsoon season
(SMS, June through September). The derived Ångström exponent
(α) decreases from a mean value of 1.1±0.03 in WMS to 0.32±0.02
in SMS, signifying a change in columnar aerosol size spectrum
from an accumulation mode dominance in WMS to a coarse mode dominance in
SMS. The composite aerosols near the surface follow suit with the share of
the accumulation mode to the total mass concentration decreasing from ~70% to
34% from WMS to SMS. The overall mass burden also decreases
in tandem. The changes in α are well correlated to those in the
accumulation fraction of the mass concentration. Long-term measurements of
the concentration of aerosol black carbon (BC), show prominent annual
variations, with its mean value decreasing from as high as 6 μg m−3
in WMS to 2 μg m−3 in SMS. Correspondingly, its mass
mixing ratio to the composite aerosols comes down from 11% to 4%.
The changes in AOD and α are significantly positively correlated to
those of BC concentration. The columnar properties are, in general well
associated with the features near the surface. The implications of these
changes to the optical properties and single scattering albedo and the
resulting impact on direct radiative forcing are examined in the companion
paper (Part 2). |
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