Structure and length scales of rotational discontinuities

Journal Article · Mon Mar 01 04:00:00 EST 1993 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/92JA02362· OSTI ID:6610609

Krauss-Varban, D ^[1]

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1. Univ. of California at San Diego, La Jolla (United States)

The author has carried out a series of one-dimensional hybrid (kinetic ions, fluid electrons) simulations, using a nondynamic method to form rotational discontinuities (RDs) at an angle of [theta][sub Bn] = 60[degrees] between the normal direction and the upstream magnetic field. Ion kinetic effects are found to be important concerning the stability of the current layer, its thickness and scaling, and its dependence on initial conditions. When the ions are initialized with transverse velocities derived from Hall MHD, RDs with both senses of rotation [alpha][sub 1] = [+-] 180[degrees] can be stable down to widths of a few c/[omega][sub pi] (ion inertial lengths). Thin RDs show a significant upstream heat flux and temperature anisotropies. Their small-scale structure is embedded in a larger envelope of the order of 100 c/[omega][sub pi]. In a cold plasma, ion-sense RDs with [alpha][sub 1] = 180[degrees] have a minimum width which scales with the ion inertial length. In a warm plasma, the thickness increases with the square root of the ion beta due to the finite ion Larmor radius. The associated breakup time increases with the initial thickness, eventually approaching the stable MHD limit for transitions very wide compared to the ion Larmor radius. Electron-sense rotations appear to be composed of a stable large amplitude [alpha][sub 1] = -360[degrees] solitary wave at the upstream edge and an ion sense [alpha][sub 1] = 90[degrees] rotation; a slight difference in speed separates the [alpha][sub 1] = 270[degrees] total rotation over time. Ionsense IDs with [alpha][sub 1] = 270[degrees] are metastable: their current structure disintegrates explosively after an initial stable interval (many 100 [Omega][sub ci][sup -1] for wide transitions, where [Omega][sub ci] is the ion cyclotron frequency), when internal ion heating has increased the average gyroradius above the width of the transition. 18 refs., 13 figs.

• OSTI ID: 6610609
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 98:A3; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

661320* -- Auroral
Ionospheric
& Magnetospheric Phenomena-- (1992-)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CHARGED PARTICLES
COLD PLASMA
COMPUTERIZED SIMULATION
CYCLOTRON FREQUENCY
DIMENSIONS
EARTH ATMOSPHERE
EARTH MAGNETOSPHERE
ELECTRONS
ELEMENTARY PARTICLES
FERMIONS
FLUID MECHANICS
HEAT FLUX
HEATING
HYDRODYNAMICS
IONS
LARMOR RADIUS
LEPTONS
MAGNETIC FIELDS
MAGNETIC RECONNECTION
MAGNETOHYDRODYNAMICS
MAGNETOPAUSE
MECHANICS
MOTION
ONE-DIMENSIONAL CALCULATIONS
PLASMA
PLASMA DRIFT
ROTATION
SCALING
SIMULATION
STABILITY
THICKNESS
VELOCITY