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Ann. Geophys., 20, 1553-1558, 2002
www.ann-geophys.net/20/1553/2002/
© European Geosciences Union 2002
Ducted compressional waves in the magnetosphere in the double-polytropic approximation
I. Ballai1,2, R. Erdélyi1, and B. Roberts2
1Atmosphere Research Center (SPARC), Dept. of Applied Mathematics, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH, England, UK
2School of Mathematics and Statistics, University of St Andrews, St Andrews, Fife, KY16 9SS, Scotland, UK
Correspondence to: I. Ballai (i.ballai@sheffield.ac.uk)
Abstract. Small-amplitude compressional
magnetohydrodynamic-type waves are studied in the magnetosphere. The
magnetosphere is treated as a rarefied plasma with anisotropy in the kinetic
pressure distribution. The parallel and perpendicular pressures are defined by
general polytropic pressure laws. This double-polytropic model can be
considered as a natural extension of the magnetohydrodynamic (MHD) model when
the plasma is collisionless.
Generalized dispersion relations for surface and body waves
are derived and analyzed for an isolated magnetic slab. The waves are confined
to the slab. For specific polytropic indices, the results obtained in the (i)
Chew-Goldberger-Low (CGL) double-adiabatic and (ii) double-isothermal
approximations are recovered.
Key words. Magnetospheric physics (MHD waves and
in-stabilities; plasma sheet; plasma waves and instabilities)
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