Other
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsm33b0448s&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #SM33B-0448
Other
2431 Ionosphere/Magnetosphere Interactions (2736), 2764 Plasma Sheet, 2784 Solar Wind/Magnetosphere Interactions
Scientific paper
Plasma in the Earth's magnetosphere is supplied from two sources; one source is the solar wind, and the other is the ionosphere. IMF Bz is thought to be one of the most important parameters that control transport of solar wind particles and ionospheric particles into the magnetosphere. For example, cold and dense plasma sheet near the flanks during the periods of northward IMF argues for solar wind entry into the plasma sheet at that time. Particle observations by Polar have shown that ionospheric particles outflow stronger during the periods of southward IMF than during the periods of northward IMF. Although various mechanisms of plasma transport have been suggested, the transport is not well understood yet. Magnetospheric plasma is mainly composed of H+, O+, N+, He+, and He2+. He2+ can be assumed to be all from the solar wind. O+ is thought to be of ionospheric origin. H+ ions come from both sources. By measuring ion composition, we can speculate the processes governing the entry, transport and acceleration of plasma in the magnetosphere and their dependence on solar wind conditions. In order to investigate the time evolution of plasma transport, we applied the method of superposed epoch analysis to H+, He2+ and O+ density variations in the plasma sheet after IMF Bz turnings. We used energetic (9-210keV/e) ion data from the Suprathermal Ion Composition Spectrometer (STICS) sensor of the Energetic Particle and Ion Composition (EPIC) instrument on GEOTAIL. Number density of H+, He2+ and O+ were estimated by fitting the kappa distribution function to the observed energy spectrum. We limited GEOTAIL position to X < 0 Re and -20 Re < Y < 20 Re in the GSM coordinate. We surveyed the data from February 1998 through November 2003. IMF data obtained from ACE/MAG were used. We found that in the near-Earth region ( X < 0 Re and radial distance of < 15 Re), the He2+ density increases for about 3 hours after the IMF Bz northward turning and then stays at constant level. This suggests that the characteristic time of the solar wind transport is about 3 hours. The O+ density did not show prominent variations during 4 hours after both northward and southward turnings. There are two possibilities that are accountable for this result. One is that O+ density in the plasma sheet is not affected by IMF Bz, although O+ outflow depends on IMF Bz. The other is that it takes greater than about 4 hours for O+ to move from the ionosphere to the plasma sheet. We will show results of H+, He2+ and O+ density variations in detail and discuss effects of energy range that does not cover < 9keV/e.
Christon Stephen P.
Keika Kunihiro
Nose Mikiha
Souma K.
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