 |
| Titel |
The complete spectrum of the equatorial electrojet related to solar tides: CHAMP observations |
| VerfasserIn |
H. Lühr, C. Manoj |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
0992-7689
|
| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 31, no. 8 ; Nr. 31, no. 8 (2013-08-05), S.1315-1331 |
| Datensatznummer |
250086086
|
| Publikation (Nr.) |
 copernicus.org/angeo-31-1315-2013.pdf |
|
|
|
|
|
| Zusammenfassung |
| Based on 10 yr of magnetic field measurements by the CHAMP satellite we draw
a detailed picture of the equatorial electrojet (EEJ) tidal variations. For the first time the
complete EEJ spectrum related to average solar tides has been compiled. A
large fraction of the resulting spectrum is related to the switch on/off of
the EEJ between day and night. This effect has carefully been considered when
interpreting the results. As expected, largest amplitudes are caused by the
migrating tides representing the mean diurnal variation. Higher harmonics of
the daily variations show a 1/f fall-off in amplitude. Such a spectrum is
required to represent the vanishing of the EEJ current at night. The
migrating tidal signal exhibits a distinct annual variation with large
amplitudes during December solstice and equinox seasons but a depression by a
factor of 1.7 around June–July. A rich spectrum of non-migrating tidal
effects is deduced. Most prominent is the four-peaked longitudinal pattern
around August. Almost 90% of the structure can be attributed to the
diurnal eastward-propagating tide DE3. In addition the westward-propagating
DW5 is contributing to wave-4. The second-largest non-migrating tide is the
semi-diurnal SW4 around December solstice. It causes a wave-2 feature in
satellite observations. The three-peaked longitudinal pattern, often quoted
as typical for the December season, is significantly weaker. During the
months around May–June a prominent wave-1 feature appears. To first order it
represents a stationary planetary wave SPW1 which causes an intensification of
the EEJ at western longitudes beyond 60° W and a weakening over
Africa/India. In addition, a prominent ter-diurnal non-migrating tide TW4
causes the EEJ to peak later, at hours past 14:00 local time in the western
sector. A particularly interesting non-migrating tide is the semi-diurnal
SW3. It causes largest EEJ amplitudes from October through December. This
tidal component shows a strong dependence on solar flux level with increasing
amplitudes towards solar maximum. We are not aware of any previous studies
mentioning this behaviour of SW3. The main focus of this study is to present
the observed EEJ spectrum and its relation to tidal driving. For several of
the identified spectral components we cannot offer convincing explanations
for the generation mechanisms. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|