Ballooning instability and structure of diamagnetic hydromagnetic waves in a model magnetosphere

Journal Article · Wed Nov 01 00:00:00 EST 1989 · Journal of Geophysical Research; (USA)

DOI:https://doi.org/10.1029/JA094iA11p15231· OSTI ID:5832152

Miura, A; Ohtani, S; Tamao, T ^[1]

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1. Univ. of Tokyo (Japan)

A linear eigenmode analysis of ballooning instability of an Alfven wave and a drift-Alfven wave is performed for a curved magnetic field line configuration in finite-{beta} plasma to examine stability of the tail plasma sheet and to find a generation mechanism of diamagnetic storm time Pc 5 pulsations, which are characterized by a large azimuthal mode number (m>50). Only fundamental mode is unstable to the ballooning instability, which is driven by the pressure gradient combined with the unfavorable magnetic field line curvature, while higher harmonic modes are stable. The eigenfunction of the unstable wave (fundamental mode) is evanescent or decaying exponential toward the ionosphere along the field line and strongly confined near the equator with its plasma pressure and magnetic pressure being out of phase. The stable higher harmonic modes, on the other hand, have standing Alfven mode structures along the field line and have frequencies determined by oscillation periods of the standing Alfven modes. In the absence of the coupling to the drift wave, the unstable fundamental wave is aperiodic with zero real frequency. When the unstable fundamental wave is coupled to the drift wave; however, the unstable wave (drift-Alfven wave) has a real frequency determined by an ion diamagnetic drift speed. The obtained oscillation period of a few hundred seconds for the unstable drift-Alfven wave with an azimuthal number m = 50, its westward propagation, diamagnetic relationship between the perturbed magnetic and plasma pressures, and strong spatial confinement of the unstable wave near the equator suggest of the authors that the unstable drift-Alfven wave destabilized by the ballooning instability is a strong candidate mechanism for explaining the observed storm time Pc 5 pulsations.

• OSTI ID: 5832152
• Journal Information: Journal of Geophysical Research; (USA), Vol. 94:A11; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
EARTH MAGNETOSPHERE
BALLOONING INSTABILITY
HYDROMAGNETIC WAVES
ALFVEN WAVES
BETA RATIO
EQUATOR
IONOSPHERE
MAGNETIC FIELD CONFIGURATIONS
MAGNETIC STORMS
MATHEMATICAL MODELS
PLASMA DRIFT
PLASMA PRESSURE
PLASMA SHEET
PRESSURE GRADIENTS
WAVE PROPAGATION
EARTH ATMOSPHERE
INSTABILITY
PLANETARY IONOSPHERES
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
640201* - Atmospheric Physics- Auroral
Ionospheric
& Magetospheric Phenomena