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| Titel |
Improved retrieval of direct and diffuse downwelling surface shortwave flux in cloudless atmosphere using dynamic estimates of aerosol content and type: application to the LSA-SAF project |
| VerfasserIn |
X. Ceamanos, D. Carrer, J.-L. Roujean |
| 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 ; 14, no. 15 ; Nr. 14, no. 15 (2014-08-15), S.8209-8232 |
| Datensatznummer |
250118950
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| Publikation (Nr.) |
 copernicus.org/acp-14-8209-2014.pdf |
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| Zusammenfassung |
| Downwelling surface shortwave flux (DSSF) is a key parameter to addressing
many climate, meteorological, and solar energy issues. Under clear sky conditions,
DSSF is particularly sensitive to the variability both in time and space of
the aerosol load and chemical composition. Hitherto, this dependence has not been
properly addressed by the Satellite Application Facility on Land Surface Analysis
(LSA-SAF), which operationally disseminates instantaneous DSSF products over the
continents since 2005 considering constant aerosol conditions. In the present
study, an efficient method is proposed for DSSF retrieval that will overcome
the limitations of the current LSA-SAF product. This method referred to as
SIRAMix (Surface Incident Radiation estimation using Aerosol Mixtures) is
based upon an accurate physical parameterization coupled with a radiative
transfer-based look up table of aerosol properties. SIRAMix considers a tropospheric
layer composed of several major aerosol species that are conveniently mixed
to reproduce real aerosol conditions as best as possible. This feature of SIRAMix allows it to
provide not only accurate estimates of global DSSF but also the direct and
diffuse DSSF components, which are crucial radiative terms in many climatological
applications. The implementation of SIRAMix is tested in the present article
using atmospheric analyses from the European Center for Medium-Range Weather
Forecasts (ECMWF). DSSF estimates provided by SIRAMix are compared against
instantaneous DSSF measurements taken at several ground stations belonging
to several radiation measurement networks. Results show an average root
mean square error (RMSE) of 23.6, 59.1, and 44.9 W m−2 for global, direct,
and diffuse DSSF, respectively. These scores decrease the average RMSE
obtained for the current LSA-SAF product by 18.6%, which only provides
global DSSF for the time being, and, to a lesser extent, for the state
of the art in the matter of DSSF retrieval (RMSE decrease of 10.9, 6.5,
and 19.1% for global, direct, and diffuse DSSF with regard to the McClear
algorithm).
The main limitation of the proposed approach is its high sensitivity to the quality of the ECMWF aerosol
inputs, which is proved to be sufficiently accurate for reanalyses
but not for forecast data.
Given the proximity of DSSF retrieval to the modeling of the atmospheric direct effect,
SIRAMix is also able to quantify the direct radiative forcing at the surface due to a given atmospheric
component (e.g., gases or aerosols). |
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