Magnetohydrodynamic theory of field line resonances in the magnetosphere

Journal Article · Thu Jul 01 04:00:00 EDT 1993 · Journal of Geophysical Research

DOI:https://doi.org/10.1029/93JA00505· OSTI ID:233030

Cheng, C Z ^[1]; Chang, T C; Lin, C A ^[2]

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1. Princeton Univ., NJ (United States)
2. and others

The linearized ideal magnetohydrodynamic (MHD) equations are cast into a set of global differential equations from which the field line resonance equations of the shear Alfven waves and slow magnetosonic waves are obtained naturally for finite beta plasmas in general magnetic field geometries with flux surfaces. The coupling between the shear Alfven waves and the magnetosonic waves is through the combined effects of geodesic magnetic field curvature and plasma pressure. For axisymmetric magnetospheric equilibria there is no coupling between the shear Alfven waves and the slow magnetosonic waves because the geodesic magnetic field curvature vanishes. The authors derive the asymptotic singular solutions of the MHD equations near the field line resonant surface. They perform numerical solutions of the field line resonance equations for a dipole magnetic field with constant plasma pressure and density along the magnetic field line. Similar to previous studies, the shear Alfven wave field line resonant frequency is roughly given by {omega} {approx} cL{sup {minus}4}{rho}{sup {minus}1/2}, where the coefficient c is roughly constant with respect to the L shell distance and {rho} is the plasma mass density. The slow magnetosonic wave resonant frequency is roughly proportional to P/{rho}L{sup 2}, where P is the plasma pressure, and is much smaller than the shear Alfven wave resonant frequency even for equatorial plasma beta as high as unity. 33 refs., 4 figs., 2 tabs.

• Sponsoring Organization: USDOE
• OSTI ID: 233030
• Journal Information: Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: A7 Vol. 98; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
ALFVEN WAVES
COUPLING
EARTH MAGNETOSPHERE
GEOMAGNETIC FIELD
HYDRODYNAMICS
MAGNETIC FIELDS
MAGNETOACOUSTIC WAVES
MAGNETOHYDRODYNAMICS
RESONANCE