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Seki et al. 1999
Seki, K., Hirahara, M., Terasawa, T., Mukai, T. and Kokubun, S. (1999). Properties of He+ beams observed by Geotail in the lobe/mantle regions: Comparison with O+ beams. Journal of Geophysical Research 104: doi: 10.1029/1998JA900142. issn: 0148-0227.

In the lobe/mantle regions of Earth's magnetotail (<210RE), the Geotail spacecraft sometimes observed multicomposition ion flows consisting of both ionospheric (H+/He+/O+) and solar wind (H+/He++) ions. Statistics on the He+ beams show that they were observed under similar conditions to those of the O+ beams reported previously. Namely, the heavy ion beams of ionospheric origin tend to exist during geomagnetically active periods in the mantle-like regions of high plasma beta, where ions of solar wind origin are the major component. The total duration of identified He+ events amounts to 3% of the total observation time in the lobe/mantle region, while that of O+ events amounts to 13%. A remarkable point is that on a short timescale, the He+ and O+ beams often appear to exist nearly exclusively. That is to say, their densities sometimes vary in an opposite sense, even when He+ and O+ coexist. If the O+ and He+ ions are given the same energy in a source region, the initial distribution function of He+ has twice the peak velocity of that of O+, and their alternating appearance and density anticorrelation in the lobe/mantle are easily explained due to the velocity filter effect. Thus the anticorrelation of their densities may suggest that ionospheric ions have undergone an energization which leads to a different velocity for different ion species. A mechanism leading to the same velocity, on the other hand, would require an alternating enhancement of the He+ and O+ fluxes in a source region to explain the anticorrelation of the densities. ¿ 1999 American Geophysical Union

BACKGROUND DATA FILES

Abstract

Keywords
Magnetospheric Physics, Magnetospheric configuration and dynamics, Magnetospheric Physics, Magnetotail, Magnetospheric Physics, Magnetotail boundary layers, Magnetospheric Physics, Magnetosphere/ionosphere interactions, Interplanetary Physics, Ejecta, driver gases, and magnetic clouds, Interplanetary Physics, Interplanetary magnetic fields, Space Plasma Physics, Numerical simulation studies
Journal
Journal of Geophysical Research
http://www.agu.org/journals/jb/
Publisher
American Geophysical Union
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