Kinetic Ballooning Instability for Substorm Onset and Current Disruption Observed by AMPTE/CCE Page: 1 of 6
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To be submitted to Geophysical Research Letters, 1998.
Kinetic Ballooning Instability for Substorm Onset and
Current Disruption Observed by AMPTE/CCE
C. Z. Cheng
Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543
A. T. Y. Lui
Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723
Abstract. A new scenario of AMPTE/CCE observation of substorm onset
and current disruption and the corresponding physical processes is presented.
Toward the end of late growth phase plasma / increases to > 50 and a low
frequency instability with a wave period of 50 - 75 seconds is excited and
grows exponentially to a large amplitude at the onset of current disruption.
At the current disruption 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 plasma pressure and velocity
profiles so that the ambient magnetic field recovers from a tail-like geometry
to a more dipole-like geometry. To understand the excitation of the low
frequency global instability, a new theory of kinetic ballooning instability
(KBI) is proposed to explain the high critical / threshold (/c 50) of the low
frequency global instability observed by the AMPTE/CCE. The stabilization
is mainly due to kinetic effects of trapped electrons and finite ion Larmor
radii which give rise to a large parallel electric field and hence a parallel
current that greatly enhances the stabilizing effect of field line tension to the
ballooning mode. As a result /c for excitation of KBI is greatly increased
over the ideal MHD ballooning instability threshold by O(102). The
wave-ion magnetic drift resonance effect produces a perturbed resonant ion
velocity distribution with a duskward velocity roughly equal to the average
ion magnetic (VB and curvature) drift velocity. Higher frequency instabilities
such as cross-field current instability (CCI) can be excited by the additional
velocity space free energy associated with the positive slope in the perturbed
resonant ion velocity distribution in the current disruption phase.
Introduction the ion thermal velocity is found near the local mid-
night sector which could lead to the excitation of the
A critical process in the previously established view cross-field current instability (CCI) during the cross
of the substorm onset and current disruption based tail current disruption phase [Lui, 1996]. In this pa-
on the observation of AMPTE/CCE spacecraft is the per a new scenario of the AMPTE/CCE observation
explosive growth phase (which lasts - 30 seconds) of substorm explosive growth phase, onset and current
at the approach of current disruption onset [Ohtani disruption is presented. In particular, toward the end
et al., 1992]. During the explosive growth phase a of late growth phase (approximately 2 minutes before
large upsurge in the duskward ion bulk drift to nearly the onset of current disruption) plasma pressure be-
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Cheng, C.Z. & Lui, A.T.Y., PPPL. Kinetic Ballooning Instability for Substorm Onset and Current Disruption Observed by AMPTE/CCE, report, May 1, 1998; Princeton, New Jersey. (digital.library.unt.edu/ark:/67531/metadc675943/m1/1/: accessed December 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.