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Electrostatic Rossby-type ion plasma waves

Published online by Cambridge University Press:  13 March 2009

J. F. McKenzie  and
M. K. Dougherty
J. F. McKenzie
Affiliation:
Department of Mathematics and Applied Mathematics, University of Natal, King George V Avenue, Durban, Natal 4001, South Africa
M. K. Dougherty
Affiliation:
Department of Mathematics and Applied Mathematics, University of Natal, King George V Avenue, Durban, Natal 4001, South Africa
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Abstract

It is shown that a plasma in which the background magnetic field varies in a direction perpendicular to its line of action can support ‘Rossby-type’ electrostatic waves at frequencies very much less than the ion gyrofrequency. The intrinsic wave propagation mechanism at work is structurally similar to that in the atmospheric Rossby wave, which comes about from fluid perturbations being in quasi-geostrophic equilibrium (i.e. the Coriolis force nearly balances the pressure gradient) and the latitudinal variation of the vertical component of rotational frequency vector (the β-effect) so that the time rate of change of the vertical component of the fluid vorticity is equal to the northward transport of the planetary vorticity. In a plasma this ‘geostrophic balance’ arises from the near-vanishing of the Lorentz force on the ion motion while the β-effect is provided by the transverse spatial variation of the ambient magnetic field. Unlike the atmosphere, however, such a magnetized plasma is capable of supporting two distinct types of Rossby wave. The interesting dispersive and anisotropic features of these waves are revealed by the properties of their wave operators and described in terms of the geometry of their wavenumber surfaces. Since these surfaces intersect, inhomogeneity or nonlinearity will give rise to strong mode-mode coupling in regions where the phases of both modes nearly match.

Type
Research Article
Information
Journal of Plasma Physics , Volume 39 , Issue 1 , February 1988 , pp. 103 - 114
Copyright
Copyright © Cambridge University Press 1988

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References

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