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| Titel |
Dust aerosols over India and adjacent continents retrieved using METEOSAT infrared radiance Part II: quantification of wind dependence and estimation of radiative forcing |
| VerfasserIn |
S. Deepshikha, S. K. Satheesh, J. Srinivasan |
| 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 ; 24, no. 1 ; Nr. 24, no. 1 (2006-03-07), S.63-79 |
| Datensatznummer |
250015458
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| Publikation (Nr.) |
 copernicus.org/angeo-24-63-2006.pdf |
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| Zusammenfassung |
| Long-range transport of continental dust makes these
particles a significant constituent even at locations far from their
sources. It is important to study the temporal variations in dust loading
over desert regions and the role of meteorology, in order to assess its
radiative impact. In this paper, infrared radiance (10.5-12.5 µm),
acquired by the METEOSAT-5 satellite (~5-km resolution) during 1999 and
2003 was used to quantify wind dependence of dust aerosols and to estimate
the radiative forcing. Our analysis shows that the frequency of occurrence of
dust events was higher during 2003 compared to 1999. Since the dust
production function depends mainly on the surface wind speed over regions which
are dry and without vegetation, the role of surface wind on IDDI was examined
in detail. It was found that an increase of IDDI with wind speed was nearly
linear and the rate of increase in IDDI with surface wind was higher during
2003 compared to 1999. It was also observed that over the Indian desert, when
wind speed was the highest during monsoon months (June to August), the dust
production rate was lower because of higher soil moisture (due to monsoon
rainfall). Over the Arabian deserts, when the wind speed is the highest during June to
August, the dust production rate is also highest, as soil moisture is lowest
during this season. Even though nothing can be said precisely on the reason
why 2003 had a greater number of dust events, examination of monthly mean soil
moisture at source regions indicates that the occurrence of high winds
simultaneous with high soil moisture could be the reason for the decreased dust
production efficiency in 1999. It appears that the deserts of Northwest India
are more efficient dust sources compared to the deserts of Saudi Arabia and
Northeast Africa (excluding Sahara). The radiative impact of dust over various
source regions is estimated, and the regionally and annually averaged top of
the atmosphere dust radiative forcing (short wave, clear-sky and over land)
over the entire study region (0-35° N; 30°-100° E) was in the
range of -0.9 to +4.5 Wm-2. The corresponding values at the surface
were in the range of -10 to -25 Wm-2. Our studies demonstrate that
neglecting the diurnal variation of dust can cause errors in the estimation of
long wave dust forcing by as much as 50 to 100%, and nighttime retrieval
of dust can significantly reduce the uncertainties. A method to retrieve
dust aerosols during nighttime is proposed. The regionally and annually
averaged long wave dust radiative forcing was +3.4±1.6 Wm-2. |
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