Abstract
Ionospheric-origin O + ions consititute an important and some times dominant part of the ring current and the near-Earth plasma sheet region during geomagnetic storms and substorms. Low-frequency instabilities excited by the energetic oxygen ions in the near-Earth plasma sheet and ring current region during the geomagnetic storms/substorms are investigated. It is shown that the presence of ionospheric-origin oxygen ion beams with anisotropic pressure can excite helicon mode instability in the near-Earth plasma sheet region provided their Alfvenic Mach numbers lie in a certain range. The helicon modes are easily excited under the conditions when the usual long wavelengths fire-hose modes are stable. On the other hand, low-frequency quasi-electrostatic loss-cone type instabilities can be driven by the energetic oxygen ions in the storm time ring current region. These instabilities may scatter ring current particles and contribute to the ring-current decay.
Published Version
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