Physics
Scientific paper
Apr 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999jgr...104.6973s&link_type=abstract
Journal of Geophysical Research, Volume 104, Issue A4, p. 6973-6986
Physics
10
Magnetospheric Physics: Magnetospheric Configuration And Dynamics, Magnetospheric Physics: Magnetotail, Magnetospheric Physics: Magnetotail Boundary Layers, Magnetospheric Physics: Magnetosphere/Ionosphere Interactions
Scientific paper
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.
Hirahara Masafumi
Kokubun Susumu
Mukai Tadashi
Seki Kazuhiko
Terasawa Toshio
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