Linear theory of the Kelvin-Helmholtz instability in the low-latitude boundary layer

Journal Article · Sat Jun 01 00:00:00 EDT 1991 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/91JA00253· OSTI ID:5256802

Rajaram, R; Sibeck, D G; McEntire, R W ^[1]

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1. Johns Hopkins Univ., Laurel, MD (USA)

The authors examine the stability of the magnetospheric low-latitude boundary layer to the Kelvin-Helmholtz instability taking into account the finite thickness of the velocity shear layer, the relative thickness and position of the current layer in which the magnetic field rotates from magnetosheath to magnetospheric configurations, and the collisionless and anisotropic nature of the plasmas therein. They show that three factors enhance the instability: (1) a decrease in the thickness of the shear layer, (2) a decrease in the thickness of the current layer (relative to the shear layer), and (3) the proximity of the current layer to the outer edge of the shear layer. Although the maximum growth rate occurs for wave numbers roughly equal to the inverse of the semithickness of the shear layer, the velocity threshold for the onset of the instability is insensitive to the thickness. However, when the current layer is displaced from the center toward the outer edge of the shear layer, the threshold is dramatically reduced and the boundary layer can be rendered unstable by relatively small shear flows, suggesting that even the region close to the subsolar point could become unstable when the sheath flow is perpendicular to the magnetospheric magnetic field. This mode can be identified by characteristic profiles across the boundary layer: the plasma density, pressure, and magnetic field strength perturbations all peak near the center of the boundary layer. The transverse magnetic field fluctuations are largest around the current layer, while the radial motions dominate near the inner edge of the boundary layer.

• OSTI ID: 5256802
• Journal Information: Journal of Geophysical Research; (United States), Vol. 96:A6; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
EARTH MAGNETOSPHERE
HELMHOLTZ INSTABILITY
BOUNDARY LAYERS
COLLISIONLESS PLASMA
MAGNETIC FIELD CONFIGURATIONS
MAGNETOPAUSE
MAGNETOSHEATH
PLASMA DENSITY
PLASMA PRESSURE
SHEAR
THICKNESS
DIMENSIONS
EARTH ATMOSPHERE
INSTABILITY
LAYERS
PLASMA
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
640201* - Atmospheric Physics- Auroral
Ionospheric
& Magetospheric Phenomena