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| Titel |
Mean diurnal variations of noctilucent clouds during 7 years of lidar observations at ALOMAR |
| VerfasserIn |
J. Fiedler, G. Baumgarten, G. Cossart |
| 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 ; 23, no. 4 ; Nr. 23, no. 4 (2005-06-03), S.1175-1181 |
| Datensatznummer |
250015213
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| Publikation (Nr.) |
 copernicus.org/angeo-23-1175-2005.pdf |
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| Zusammenfassung |
| From 1997 to 2003, noctilucent clouds (NLC) were observed by lidar
above the ALOMAR observatory in Northern Norway (69° N) during
a total of 1880 measurement hours. This data set contains NLC
signatures for 640h, covering all local times, even during the
highest solar background conditions. After data limitation
imposing a threshold value of 4x10-10m-1sr-1 for the
volume backscatter coefficient of the NLC particles, a measure for
the cloud brightness, local time dependencies of the NLC
occurrence frequency, altitude, and brightness were determined. On
average, over the 7 years NLC occurred during the whole day and
preferably in the early morning hours, with a maximum occurrence
frequency of ~40% between 4 and 7 LT. Splitting the data
into weak and strong clouds yields almost identical amplitudes of
diurnal and semidiurnal variations for the occurrence of weak
clouds, whereas the strong clouds are dominated by the diurnal
variation. NLC occurrence, altitude, as well as brightness, show a
remarkable persistence concerning diurnal and semidiurnal
variations from 1997 to 2003, suggesting that NLC above ALOMAR are
significantly controlled by atmospheric tides. The observed mean
anti-phase behavior between cloud altitude and brightness is
attributed to a phase shift between the semidiurnal components by
~6h. Investigation of data for each individual year
regarding the prevailing oscillation periods of the NLC parameters
showed different phase relationships, leading to a complex
variability in the cloud parameters. |
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