Kinetic Ballooning Instability as a Substorm Onset Mechanism

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A new scenario of substorm onset and current disruption and the corresponding physical processes are presented based on the AMPTE/CCE spacecraft observation and a kinetic ballooning instability theory. During the growth phase of substorms the plasma beta is larger than unity (20 greater than or equal to beta greater than or equal to 1). Toward the end of the late growth phase the plasma beta increases from 20 to greater than or equal to 50 in approximately 3 minutes and a low-frequency instability with a wave period of 50 - 75 sec is excited and grows exponentially to a large ... continued below

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128 Kilobytes pages

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C.Z.Cheng October 1, 1999.

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Description

A new scenario of substorm onset and current disruption and the corresponding physical processes are presented based on the AMPTE/CCE spacecraft observation and a kinetic ballooning instability theory. During the growth phase of substorms the plasma beta is larger than unity (20 greater than or equal to beta greater than or equal to 1). Toward the end of the late growth phase the plasma beta increases from 20 to greater than or equal to 50 in approximately 3 minutes and a low-frequency instability with a wave period of 50 - 75 sec is excited and grows exponentially to a large amplitude at the current disruption onset. At the onset, higher-frequency instabilities are excited so that the plasma and electromagnetic field form a turbulent state. Plasma transport takes place to modify the ambient pressure profile so that the ambient magnetic field recovers from a tail-like geometry to a dipole-like geometry. A kinetic ballooning instability (KBI) theory is proposed to explain the low-frequency instability (frequency and growth rate) and its observed high beta threshold (beta subscript c is greater than or equal to 50). Based on the ideal-MHD theory beta subscript c, superscript MHD approximately equals 1 and the ballooning modes are predicted to be unstable during the growth phase, which is inconsistent with observation that no appreciable magnetic field fluctuation is observed. The enhancement beta subscript c over beta subscript c, superscript MHD is due to the kinetic effects of trapped electrons and finite ion-Larmor radii which provide a large stabilizing effect by producing a large parallel electric field and hence a parallel current that greatly enhances the stabilizing effect of field line tension. As a result, beta subscript c is greatly increased over beta subscript c, superscript MHD by a factor proportional to the ratio of the total electron density to the untrapped electron density (n subscript e divided by n subscript eu) which is greater than or equal to O (10 superscript 2 ) in the near-Earth plasma sheet. The wave-ion magnetic drift resonance effect produces a perturbed resonant ion velocity distribution centered at a duskward velocity roughly equal to the average ion magnetic drift velocity. This perturbed ion distribution explains the enhanced duskward ion flux during the explosive growth phase and can excite higher-frequency instabilities (such as the cross-field current instability).

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128 Kilobytes pages

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INIS; OSTI as DE00014387

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  • Other Information: PBD: 1 Oct 1999

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  • Report No.: PPPL-3369
  • Grant Number: AC02-76CH03073
  • DOI: 10.2172/14387 | External Link
  • Office of Scientific & Technical Information Report Number: 14387
  • Archival Resource Key: ark:/67531/metadc619758

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  • October 1, 1999

Added to The UNT Digital Library

  • June 16, 2015, 7:43 a.m.

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  • April 15, 2016, 9:26 p.m.

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C.Z.Cheng. Kinetic Ballooning Instability as a Substorm Onset Mechanism, report, October 1, 1999; Princeton, New Jersey. (digital.library.unt.edu/ark:/67531/metadc619758/: accessed September 21, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.