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| Titel |
Total and partial cloud amount detection during summer 2005 at Westerland (Sylt, Germany) |
| VerfasserIn |
N. H. Schade, A. Macke, H. Sandmann, C. Stick |
| 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 ; 9, no. 4 ; Nr. 9, no. 4 (2009-02-16), S.1143-1150 |
| Datensatznummer |
250006916
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| Publikation (Nr.) |
 copernicus.org/acp-9-1143-2009.pdf |
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| Zusammenfassung |
The detection of cloudiness is investigated by means of partial and total
cloud amount estimations from pyrgeometer radiation measurements and visible
all-sky imager observations. The measurements have been performed in
Westerland, a seaside resort on the North Sea island of Sylt, Germany, during
summer 2005.
An improvement to previous studies on this subject resulting in
the first time partial cloud amounts (PCAs), defined as cloud amounts
without high clouds calculated from longwave downward radiation (LDR)
according to the APCADA algorithm (Dürr and Philipona, 2004), are
validated against both human observations from the National Meteorological
Servive DWD at the nearby airport of Sylt and digital all-sky imaging. The
aim is to establish the APCADA scheme at a coastal midlatitude site for
longterm observations of cloud cover and to quantify errors resulting from the
different methods of detecting cloudiness.
Differences between the resulting total cloud amounts (TCAs), defined as
cloud amount for all-cloud situations, derived from the camera images
and from human observations are within ±1 octa in 72% and within
±2 octa in 85% of the cases. Compared to human observations, PCA
measurements, according to APCADA, underestimate the observed cloud cover in
47% of all cases and the differences are within ±1 octa in 60% and
±2 octa in 74% of all cases. Since high cirrus clouds can not be
derived from LDR, separate comparisons for all cases without high clouds have
been performed showing an agreement within ±1(2) octa in 73(90)% for
PCA and also for camera-derived TCA. For this coastal mid-latitude site under
investigation, we find similar though slightly smaller agreements to human
observations as reported by Dürr and Philipona (2004). Though limited to
daytime, the cloud cover retrievals from the sky imager are not really affected
by cirrus clouds and provide a more reliable cloud climatology for all-cloud
conditions than APCADA. |
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