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Spectral characteristics of hydromagnetic waves in the magnetosphere

Published online by Cambridge University Press:  13 March 2009

S. P. Kuo
Affiliation:
Polytechnic University, Route 110, Farmingdale, NY 11735
M. C. Lee
Affiliation:
Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
A. Wolfe
Affiliation:
New York City Technical College of the CityUniversity of New York, Brooklyn, NY 11201

Abstract

This work is intended to explain why the resonant response of the magnetosphere prefers to have discrete frequencies. Using a cylindrical model for the outer magnetosphere with a plasma density profile proportional to 1/r, we show that the eigenequation characterizing the eigenmodes of the hydromagnetic waves in this model has two turning points along the radial axis. The locations of the turning points depend upon the values of the eigenperiod and the associated east-west wavenumber of the eigenmode. The energy spectrum of the excited cavity modes is seen to have sharp peaks at discrete frequencies when the surface perturbations have a uniform spectrum in the frequency range of interest. We, therefore, have also shown that only the discrete set of the magnetospheric cavity eigenmodes can efficiently couple the perturbations excited on the boundary of the magnetosphere to the field-line resonant mode excited inside the inner turning point of the cavity eigenmode. The most likely values of east-west wavenumbers and wave period range are determined.

Type
Research Article
Copyright
Copyright © Cambridge University Press 1987

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