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| Titel |
Some implications of sampling choices on comparisons between satellite and model aerosol optical depth fields |
| VerfasserIn |
A. M. Sayer, G. E. Thomas, P. I. Palmer, R. G. Grainger |
| 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 ; 10, no. 22 ; Nr. 10, no. 22 (2010-11-16), S.10705-10716 |
| Datensatznummer |
250008890
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| Publikation (Nr.) |
 copernicus.org/acp-10-10705-2010.pdf |
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| Zusammenfassung |
| The comparison of satellite and model aerosol optical depth (AOD)
fields provides useful information on the strengths and weaknesses of
both. However, the sampling of satellite and models is very different
and some subjective decisions about data selection and aggregation
must be made in order to perform such comparisons. This work examines
some implications of these decisions, using GlobAerosol AOD retrievals
at 550 nm from Advanced Along-Track Scanning Radiometer
(AATSR) measurements, and aerosol fields from the GEOS-Chem chemistry
transport model. It is recommended to sample the model only where the
satellite flies over on a particular day; neglecting this can cause
regional differences in model AOD of up to 0.1 on monthly and annual
timescales. The comparison is observed to depend strongly upon
thresholds for sparsity of satellite retrievals in the model grid
cells. Requiring at least 25% coverage of the model grid cell by
satellite data decreases the observed difference between the two by
approximately half over land. The impact over ocean is smaller. In
both model and satellite datasets, there is an anticorrelation between
the proportion p of a model grid cell covered by satellite
retrievals and the AOD. This is attributed to small p typically
occuring due to high cloud cover and lower AODs being found in large
clear-sky regions. Daily median AATSR AODs were found to be closer to
GEOS-Chem AODs than daily means (with the root mean squared difference
being approximately 0.05 smaller). This is due to the decreased
sensitivity of medians to outliers such as cloud-contaminated
retrievals, or aerosol point sources not included in the model. |
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