Limits on plasma anisotropy in a tail-like magnetic field

Journal Article · Thu Dec 24 00:00:00 EST 1992 · Geophysical Research Letters (American Geophysical Union); (United States)

DOI:https://doi.org/10.1029/92GL02497· OSTI ID:7061935

Hill, T W; Voigt, G H ^[1]

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1. Rice Univ., Houston, TX (United States)

Understanding the static balance of forces in a hypothetical stationary, steady-state magnetotail configuration is central to our understanding of planetary magnetotail dynamics, even though the actual planetary magnetotails may rarely if ever attain such a steady state. We are not likely to achieve an understanding of the observed departures from equilibrium if we do not first understand the nature of the equilibrium itself, albeit hypothetical. The condition of magnetohydrostatic equilibrium implies tight constraints on the degree of anisotropy that is supportable in a magnetotail field geometry. If the plasma pressure tensor is assumed to be gyrotropic at the tail midplane (z = 0), then equilibrium requires that it also be nearly isotropic there, with P[sub [perpendicular]0]/P[sub [parallel]0] in the range 1 [plus minus] [delta][sup 2], where [delta] [approximately] 0.1 is the ratio of the normal field component at the symmetry plane to the field strength in the tail lobe. The upper and lower limits are essentially equivalent, respectively, to the marginal mirror and firehose stability conditions evaluated at z = 0, which have been invoked previously to limit the degree of anisotropy in the plasma sheet. 21 refs., 1 fig.

• OSTI ID: 7061935
• Journal Information: Geophysical Research Letters (American Geophysical Union); (United States), Vol. 19:24; ISSN 0094-8276
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
MAGNETOTAIL
EQUILIBRIUM
PLASMA
PLASMA PRESSURE
ANISOTROPY
CONSTRAINTS
GEOMETRY
HOSE INSTABILITY
MAGNETIC FIELDS
PLASMA INSTABILITY
PLASMA SHEET
SYMMETRY
EARTH ATMOSPHERE
EARTH MAGNETOSPHERE
INSTABILITY
MATHEMATICS
PLASMA MICROINSTABILITIES
661320* - Auroral
Ionospheric
& Magnetospheric Phenomena- (1992-)