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| Titel |
Global characteristics of the lunar tidal modulation of the equatorial electrojet derived from CHAMP observations |
| VerfasserIn |
H. Lühr, T. A. Siddiqui, S. Maus |
| 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 ; 30, no. 3 ; Nr. 30, no. 3 (2012-03-08), S.527-536 |
| Datensatznummer |
250017198
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| Publikation (Nr.) |
 copernicus.org/angeo-30-527-2012.pdf |
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| Zusammenfassung |
It has been known since many decades that lunar tide has an influence on the
strength of the equatorial electrojet (EEJ). There has, however, never been
a comprehensive study of the tidal effect on a global scale. Based on the
continuous magnetic field measurements by the CHAMP satellite over 10 years
it is possible to investigate the various aspects of lunar effects on the
EEJ. The EEJ intensity is enhanced around times when the moon is overhead or
at the antipode. This effect is particularly strong around noon, shortly
after new and full moon. The lunar tide manifests itself as a semi-diurnal
wave that precesses through all local times within one lunar month. The
largest tidal amplitudes are observed around December solstice and smallest
around June solstice. The tidal wave crest lags behind the moon phase.
During December this amounts to about 4 days while it is around 2 days
during other times of the year. We have not found significant longitudinal
variations of the lunar influence on the EEJ. When comparing the average EEJ
amplitude at high solar activity with that during periods of solar minimum
conditions a solar cycle dependence can be found, but the ratio between
tidal amplitude and EEJ intensity stays the same. Actually, tidal signatures
standout clearer during times of low solar activity. We suggest that the
tidal variations are caused by a current system added to the EEJ rather than
by modulating the EEJ. Gravitational forcing of the lower atmosphere by the
moon and the sun is assumed to be the driver of an upward propagating tidal
wave. The larger tidal amplitudes around December solstice can be related to
stratospheric warming events which seem to improve the conditions for upward
propagation.
The results described here have to large extent been presented as a
Julius-Bartels Medal Lecture during the General Assembly 2011 of the
European Geosciences Union. |
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