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Titel |
Interpretation of FRESCO cloud retrievals in case of absorbing aerosol events |
VerfasserIn |
P. Wang, O. N. E. Tuinder, L. G. Tilstra, M. Graaf, P. Stammes |
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. 19 ; Nr. 12, no. 19 (2012-10-04), S.9057-9077 |
Datensatznummer |
250011494
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Publikation (Nr.) |
copernicus.org/acp-12-9057-2012.pdf |
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Zusammenfassung |
Cloud and aerosol information is needed in trace gas retrievals from
satellite measurements. The Fast REtrieval Scheme for Clouds from the Oxygen
A band (FRESCO) cloud algorithm employs reflectance spectra of the O2 A
band around 760 nm to derive cloud pressure and effective cloud fraction. In
general, clouds contribute more to the O2 A band reflectance than
aerosols. Therefore, the FRESCO algorithm does not correct for aerosol
effects in the retrievals and attributes the retrieved cloud information
entirely to the presence of clouds, and not to aerosols. For events with high
aerosol loading, aerosols may have a dominant effect, especially for almost
cloud free scenes. We have analysed FRESCO cloud data and Absorbing Aerosol
Index (AAI) data from the Global Ozone Monitoring Experiment (GOME-2)
instrument on the Metop-A satellite for events with typical absorbing aerosol
types, such as volcanic ash, desert dust and smoke. We find that the FRESCO
effective cloud fractions are correlated with the AAI data for these
absorbing aerosol events and that the FRESCO cloud pressure contains
information on aerosol layer pressure. For cloud free scenes, the derived
FRESCO cloud pressure is close to the aerosol layer pressure, especially for optically
thick aerosol layers. For cloudy scenes, if the strongly absorbing aerosols are
located above the clouds, then the retrieved FRESCO cloud pressure may
represent the height of the aerosol layer rather than the height of the
clouds. Combining FRESCO and AAI data, an estimate for the aerosol
layer pressure can be given. |
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