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Title: Kinetic Ballooning Instability for Substorm Onset and Current Disruption Observed by AMPTE/CCE

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 beta increases to greater than or equal 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 magnetic 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 beta threshold (the high critical beta threshold is greater than or equal to 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 tomore » the ballooning mode. As a result, the high critical beta threshold for excitation of KBI is greatly increased over the ideal-MHD ballooning instability threshold by greater than or equal to O(10 exp 2). 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 (gradient B 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.« less

Authors:
;
Publication Date:
Research Org.:
Princeton Univ., NJ (United States). Plasma Physics Lab.
Sponsoring Org.:
USDOE Office of Energy Research, Washington, DC (United States)
OSTI Identifier:
289896
Report Number(s):
PPPL-3299
ON: DE98059563
DOE Contract Number:
AC02-76CH03073
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: May 1998
Country of Publication:
United States
Language:
English
Subject:
66 PHYSICS; BALLOONING INSTABILITY; IONOSPHERIC STORMS

Citation Formats

Cheng, C.Z., and Lui, A.T.Y., PPPL. Kinetic Ballooning Instability for Substorm Onset and Current Disruption Observed by AMPTE/CCE. United States: N. p., 1998. Web. doi:10.2172/289896.
Cheng, C.Z., & Lui, A.T.Y., PPPL. Kinetic Ballooning Instability for Substorm Onset and Current Disruption Observed by AMPTE/CCE. United States. doi:10.2172/289896.
Cheng, C.Z., and Lui, A.T.Y., PPPL. Fri . "Kinetic Ballooning Instability for Substorm Onset and Current Disruption Observed by AMPTE/CCE". United States. doi:10.2172/289896. https://www.osti.gov/servlets/purl/289896.
@article{osti_289896,
title = {Kinetic Ballooning Instability for Substorm Onset and Current Disruption Observed by AMPTE/CCE},
author = {Cheng, C.Z. and Lui, A.T.Y., PPPL},
abstractNote = {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 beta increases to greater than or equal 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 magnetic 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 beta threshold (the high critical beta threshold is greater than or equal to 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, the high critical beta threshold for excitation of KBI is greatly increased over the ideal-MHD ballooning instability threshold by greater than or equal to O(10 exp 2). 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 (gradient B 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.},
doi = {10.2172/289896},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri May 01 00:00:00 EDT 1998},
month = {Fri May 01 00:00:00 EDT 1998}
}

Technical Report:

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  • A new scenario of AMPTE/CCE observation of substorm onset and current disruption and the corresponding physical processes is presented. Toward the end of the late growth phase, plasma beta increases to greater than or equal 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 and heating take place to reduce plasma beta and modify the ambient plasma pressure andmore » 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 beta threshold (greater than or equal to 50) of the low-frequency global instability observed by the AMPTE/CCE. The stabilization kinetic effects of trapped electron and finite ion Larmor radii 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, the high critical beta threshold for excitation of KBI is greatly increased over the ideal MHD ballooning instability threshold by greater than O(10 squared). The wave-ion magnetic drift resonance effect typically reduces the high critical beta threshold by up to 20% and produces a perturbed resonant ion velocity distribution with a duskward velocity roughly equal to the average ion magnetic drift velocity as the KBI grows to a large amplitude. Higher-frequency instabilities, such as the 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.« less
  • 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 largemore » 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).« less
  • The Active Magnetospheric Particle Tracer Explorers/Charge Composition Explorer (AMPTE/CCE), with a small inclination of 4.8/sup 0/ and an apogee of approx.8.8 R/sub E/, is capable of exploring the dynamical behavior of the near-earth magnetotial current sheet during substorms. At approx.1153 UT on day 240 (August 28), 1986, the spacecraft was on the midplane of the magnetotail near midnight (approx.23.4 h LT) at a radial distance of approx.8 R/sub E/, when the onset of a substorm took place. The magnetic field data for the approx.3.5-min interval following the onset indicated a variation of the magnetic field that has not been observedmore » by geostationary satellites or by other spacecraft flown in the near-earth tail (rapprox. <20 R/sub E/). The variation was characterized by a large-amplitude (from less than 10 nT to greater than 40 nT) oscillation of the total field with a period of approx.13 s and also by southward turning of the field during most cycles of the oscillation. At times the magnetic field became strongly southward, and in a few measurements the magnitude of the southward component exceeded 20 nT. The level of high-frequency perturbations (period shorter than approx.10 s) was also enhanced during the event. The observations may be due to the formation of an X-type neutral line and its motion near the spacecraft. copyright American Geophysical Union 1987« less
  • The relation between Pi 1-2 pulsations on the ground and substorm-associated magnetic field variations in space has been studied using data obtained on the ground at low-latitude conjugate stations (L = 1.3-2.1) and in the near-Earth magnetotail by the AMPTE CCE spacecraft. The ground-based data were acquired in a campaign period from July 20 to September 16, of 1986, during which the apogee of CCE (8.8 R{sub E}) was located between 2330 and 0230 hours magnetic local time. Of 16 clear magnetic field dipolarizations observed at CCE, all had a corresponding Pi 2 pulsation on the ground, with a timemore » lag of +1 to {minus}7 min. For most (13) of these cases, the time lag was equal to or shorter than 2 min. However, the authors also found Pi 2 pulsations that do not accompany a dipolarization at CCE. These results are consistent with previous observations, which showed that Pi 2 pulsations are a global indicator of the expansion phase onset of a substorm, whereas dipolarizations occur in a limited region in the near-Earth magnetotail. One of the 16 events, which occurred on August 28, 1986, is studied in detail because a 13-s Pi 1 pulsation was observed on the ground in addition to an ordinary Pi 2 pulsation. For this event, CCE also observed a {approximately} 13-s oscillation at {approximately} 8.1 R{sub E} in the midplane of the magnetorail near midnight (Takahashi et a., 1987). They suggest that field line resonance driven by a quasi-monochromatic oscillation in the near-Earth tail is the cause of the Pi 1 pulsation observed on the ground. The commonly observed Pi 2 pulsations could be attributed to other wave excitation mechanisms including transient response of the magnetospheric cavity to a substorm-associated impulse.« less