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| Titel |
Retrieval of dust aerosols during night: improved assessment of long wave dust radiative forcing over Afro-Asian regions |
| VerfasserIn |
S. Deepshikha, 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 ; 28, no. 8 ; Nr. 28, no. 8 (2010-08-18), S.1553-1557 |
| Datensatznummer |
250016870
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| Publikation (Nr.) |
 copernicus.org/angeo-28-1553-2010.pdf |
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| Zusammenfassung |
| Several investigators in the past have used the radiance
depression (with respect to clear-sky infrared radiance), resulting from the
presence of mineral dust aerosols in the atmosphere, as an index of dust
aerosol load in the atmosphere during local noon. Here, we have used a
modified approach to retrieve dust index during night since assessment of
diurnal average infrared dust forcing essentially requires information on
dust aerosols during night. For this purpose, we used infrared radiance
(10.5–12.5 μm), acquired from the METEOSAT-5 satellite (~ 5 km
resolution). We found that the "dust index" algorithm, valid for daytime,
will no longer hold during the night because dust is then hotter than the
theoretical dust-free reference. Hence we followed a "minimum reference"
approach instead of a conventional "maximum reference" approach. A detailed
analysis suggests that the maximum dust load occurs during the daytime. Over
the desert regions of India and Africa, maximum change in dust load is as
much as a factor of four between day and night and factor of two variations
are commonly observed. By realizing the consequent impact on long wave dust
forcing, sensitivity studies were carried out, which indicate that utilizing
day time data for estimating the diurnally averaged long-wave dust radiative
forcing results in significant errors (as much as 50 to 70%). Annually
and regionally averaged long wave dust radiative forcing (which account for
the diurnal variation of dust) at the top of the atmosphere over Afro-Asian
region is 2.6 ± 1.8 W m−2, which is 30 to 50% lower than those
reported earlier. Our studies indicate that neglecting diurnal variation of
dust while assessing its radiative impact leads to an overestimation of dust
radiative forcing, which in turn result in underestimation of the radiative
impact of anthropogenic aerosols. |
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