The influence of centrifugal forces on the B field structure of an axially symmetric equilibrium magnetosphere

Journal Article · Sat Jul 01 00:00:00 EDT 1989 · Journal of Geophysical Research; (USA)

DOI:https://doi.org/10.1029/JA094iA07p08693· OSTI ID:5913443

Ye, Gang; Voigt, G ^[1]

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1. Rice Univ., Houston, TX (USA)

The authors investigate a stationary model of a rotating, axially symmetric pole-on magnetosphere in MHD force balance. In this model both the planet's rotational and dipole axes are aligned with the magnetotail axis, which is the axis of symmetry in a cylindrical (r, {phi}, z) coordinate system. On the sunward side, the magnetosphere is closed by an appropriate image dipole. Inside the magnetospheric cavity they assume isotropic thermal plasma pressure. They assume further that, in general, planetary rotation leads to differentially rotating magnetotail field lines causing field-aligned Birkeland currents and a corresponding toroidal magnetic B{sub {phi}} component which leads to twisted magnetotail field lines. They calculate the deformation of magnetotail field lines under the influence of both thermal plasma pressure and centrifugal forces. They present linear (analytic) solutions to the Grad-Shafranov equation which include the centrifugal force term. In the linear model, two free physical parameters, k and {omega}, measure the plasma thermal pressure and the ratio between plasma rotational and thermal energy densities, respectively. Low {omega} and high k values indicate the plasma-dominated case. Conversely, low k and high {omega} values indicate the rotation-dominated case. One limiting case, k = {omega} = 0., generates a simple vacuum magnetic field of a dipole confined within the magnetospheric cavity. The nonrotational magnetosphere with hot thermal plasma leads to a field configuration without a toroidal B{sub {phi}} component and without field-aligned Birkeland currents. The other extreme, namely, a rapidly rotating magnetosphere with cold plasma, leads to a configuration in which the plasma must be confined within a thin disk in a plane where the radial magnetic field component B{sub r} vanishes locally.

• OSTI ID: 5913443
• Journal Information: Journal of Geophysical Research; (USA), Vol. 94:A7; ISSN 0148-0227
• Country of Publication: United States
• Language: English

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