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On hydromagnetic Rossby waves excited by travelling forcing effects

Published online by Cambridge University Press:  29 March 2006

M. S. Sarma  and
L. V. K. V. Sarma
M. S. Sarma
Affiliation:
Department of Mathematics, Indian Institute of Technology, Madras
L. V. K. V. Sarma
Affiliation:
Department of Mathematics, Indian Institute of Technology, Madras
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Abstract

The pattern and propagation of hydromagnetic Rossby waves excited by travelling forcing effects on a rotating spherical shell of incompressible, inviscid, perfectly conducting fluid are studied using Lighthill's technique. The basic magnetic field H0, is assumed to be uniform and acting in the ‘beta-plane’ in an arbitrary direction. The two situations when the forcing effects travel along and perpendicular to H0, are considered.

The steady forcing effects travelling in the direction of an eastward or west-ward H0, excite two types of wave systems. The first consists of uiiattenuated signals directly behind or ahead of the forcing effect. The other system consists of semicircular waves travelling in all directions or waves travelling in a limited wedge.

When the forcing effect moves eastward, perpendicular to an H0, acting northward, the waves excited in the steady case are confined to certain wedges and trail behind with cusp-shaped wave crests. The magnetic field increases the semi-angle of the wedges, so that the region of disturbance is expanded. An oscillatory forcing effect generates various systems of waves. If the frequency of oscillation exceeds a certain critical frequency, excitement of waves in all directions is possible. The situation with a westward-moving forcing effect is also discussed. The effect of large rotation is to reduce the length of the waves.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 57 , Issue 2 , 6 February 1973 , pp. 303 - 320
Copyright
© 1973 Cambridge University Press

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