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| Titel |
Electromagnetic harmonic ELF emissions close to the geomagnetic equator observed by a low-altitude satellite |
| VerfasserIn |
F. Nemec, O. Santolík, M. Parrot |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250020963
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| Zusammenfassung |
| Electromagnetic harmonic ELF emissions are electromagnetic waves observed by the low
altitude DEMETER spacecraft (altitude about 700 km) close to the geomagnetic equator.
When represented as a frequency-time spectrogram, they take form of nearly parallel and
almost horizontal clearly defined lines. They propagate in whistler mode, with the
polarization of magnetic field fluctuations being linear at the geomagnetic equator; this – as
well as their structure – corresponds to the "equatorial noise" emissions or "fast
magnetosonic waves" routinely observed at larger radial distances. We present a
detailed study of 24 such events, demonstrating both their general properties and
propagation characteristics. We show that the frequency of these events is most likely
between about 300 and 700 Hz, with the total bandwidth being below 300 Hz in
most of the cases. The events occur primarily at the geomagnetic equator, but they
may extend as far as up to 15 degrees of geomagnetic latitude. Detailed analysis of
the propagation characteristics reveals that the component of the Poynting flux
parallel to the ambient magnetic field is oriented along the magnetic field lines in the
Northern hemisphere and opposite the magnetic field lines in the Southern hemisphere,
suggesting that the generation region of the waves is located close to the equatorial
plane. The waves are coming towards the spacecraft from larger radial distances. |
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