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| Titel |
Propagation of magnetosonic and whistler-mode waves from the magnetosphere and atmosphere into the ionosphere |
| VerfasserIn |
O. Santolík, M. Parrot, J. Chum, F. Nemec |
| 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 |
250020683
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| Zusammenfassung |
| We summarize observations of the DEMETER spacecraft in the top-side ionosphere
related to the lightning activity, to the downward propagating magnetospheric chorus
emissions and to the magnetosonic harmonic ELF emissions close to the geomagnetic
equator.
At the 707 km altitude of DEMETER, we have observed 3D electric and magnetic field
waveforms of fractional-hop whistlers. We identify corresponding source lightning
strokes and we perform multidimensional analysis of the measurements and obtain
detailed information on wave polarization characteristics and propagation directions.
This allows us for the first time to combine these measurements with ray tracing
simulation in order to directly characterize how the radiation penetrates through the
ionosphere.
We also interpret observations of low-altitude electromagnetic ELF hiss observed on the
dayside at subauroral latitudes. These waves propagate with downward directed wave vectors
which are slightly equatorward inclined at lower magnetic latitudes and slightly
poleward inclined at higher latitudes. Reverse ray tracing indicates a possible source
region near the geomagnetic equator at a radial distance between 5 and 7 Earth radii
and we find that low-altitude ELF hiss contains discrete time-frequency structures
resembling wave packets of whistler mode chorus. The reverse raypaths of ELF hiss are
consistent with the hypothesis that the frequently observed dayside ELF hiss is a
low-altitude manifestation of natural magnetospheric emissions of whistler mode
chorus.
Finally, we analyze waves that propagate in the extraordinary magnetosonic mode to the
ionosphere from larger radial distances close to the plane of the geomagnetic equator. These
waves show a characteristic harmonic structure very similar to previously reported
observations of equatorial noise in the magnetosphere. The observed mode structure is
influenced by the presence of multiple ions in the plasma of the top-side ionosphere but the
spectral and propagation properties suggest that these waves origin from equatorial noise
generated at the ion cyclotron harmonics. |
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