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Author Ohtani, S. ♦ Lui, A. T. Y. ♦ Higuchi, T.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword PHYSICS ♦ MAGNETIC FIELDS ♦ FLUCTUATIONS ♦ TIME-SERIES ANALYSIS ♦ ELECTRIC CURRENTS ♦ MAGNETOTAIL ♦ MAGNETIC STORMS ♦ FRACTALS
Abstract The objective of the present study is to assess the mechanism of substorm associated tail current disruption on the basis of magnetic field observations in the near-Earth tail. The authors examined 15 events observed by the Charge Composition Explorer (CCE) of the Active Magnetospheric Particle Tracer Explorers (AMPTE), with an emphasis on the August 28, 1986, event. In these events the satellite observed magnetic fluctuations to start almost simultaneously with ground substorm onsets, strongly suggesting that these fluctuations are related to the trigger of substorms. In this study the authors applied the new method, fractal analysis, to these fluctuations. This method enables them to examine fluctuations quantitatively and to pick up characteristic timescale(s) of fluctuations, even if fluctuations are far from sinusoidal. The results are summarized as follows: (1) Whereas before the onset of tail current disruption, magnetic fluctuations are suppressed in each of the magnetic components, after the onset, the magnitude of the H (north-south) component fluctuations is about 30% larger than the magnitudes of the fluctuations of the other components. (2) The magnetic fluctuations have a characteristic timescale, which is several times the proton gyroperiod. The first result suggests that observed magnetic fluctuations are actually related to changes in the tail current intensity, that is, tail current disruption. This result also indicates that the microprocess of tail current disruption should be described in terms of turbulent perturbation electric currents, although away from the onset region the effects of tail current disruption may be approximated by those of an orderly decrease in the tail current intensity. The second result strongly suggests that tail current disruption is driven by a certain instability, which grows most rapidly around that characteristic time scale, and in which ions should play an important role. 47 refs., 9 figs., 1 tab.
ISSN 01480227
Educational Use Research
Learning Resource Type Article
Publisher Date 1995-10-01
Publisher Place United States
Journal Journal of Geophysical Research
Volume Number 100
Issue Number A10


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