Plasma Bulk Oscillations with Multiple Ion Components: Geotail Observations in the Dawnside and Duskside Regions in the Near-Earth Magnetosphere

Details Plasma Bulk Oscillations with Multiple Ion Components: Geotail Observations in the Dawnside and Duskside Regions in the Near-Earth Magnetosphere Plasma Bulk Oscillations with Multiple Ion Components: Geotail Observations in the Dawnside and Duskside Regions in the Near-Earth Magnetosphere

May 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sm42a07h&link_type=abstract

American Geophysical Union, Spring Meeting 2001, abstract #SM42A-07

Physics

2730 Magnetosphere--Inner, 2740 Magnetospheric Configuration And Dynamics, 2752 Mhd Waves And Instabilities, 7807 Charged Particle Motion And Acceleration, 7859 Transport Processes

Scientific paper

Geotail often observes low-frequency periodic plasma bulk oscillations in the equatorial regions of the near-Earth magnetosphere. The oscillation periods are 3 to 10 minutes, and the Geotail locations for these observations are in the dawnside or the duskside region in most cases. The periodic ion signatures can easily be found as flux enhancements of both lower-energy (less than a few keV) and higher-energy (more than 10 keV) ion components in general energy-time spectrograms. The plasma bulk oscillations sometimes last for more than 1.5 hours while their oscillation periods and intensities of enhanced ion fluxes often vary. The magnetic fields also periodically change in accordance with the plasma bulk oscillations. Variations of the bulk velocity vectors seem to have a linearly polarized feature during the events, which are in phase with the periodic enhancements of the lower-energy ion fluxes. It should be noted that two or three discrete ion components with different energies are clearly seen in the lower-energy ion flux enhancements of many cases. Since energy ratios among the three (two) ion signatures are roughly 1:4:16 (1:16), the ion composition could be H+, He+, and O+ (H+ and O+) from the lowest energy component. For example, the data obtained around 2105 UT on April 21, 2000 show the remarkable ion feature consisting of three cold ion components that periodically appear every 5 to 9 minutes. The periodic appearances of the discrete ion components are well correlated with ion densities calculated from the particle instrument data and the single probe data. The authors have been investigating the discrete ion signatures with multiple composition on the basis of the Akebono and Geotail data obtained in the polar magnetosphere, the lobe/mantle, the flankside magnetopause, and the plasma sheet. In addition to these previous results, the events reported here indicate that the multicomponent discrete (velocity-filtered) ion signatures consisting of two or three ion species are common features in the magnetosphere.

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