Journal cover Journal topic
Annales Geophysicae Sun, Earth, planets, and planetary systems An interactive open-access journal of the European Geosciences Union
Ann. Geophys., 20, 1553-1558, 2002
© Author(s) 2002. This work is distributed under
the Creative Commons Attribution 3.0 License.
31 Oct 2002
Ducted compressional waves in the magnetosphere in the double-polytropic approximation
I. Ballai2,1, 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 (
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)

Citation: Ballai, I., Erdélyi, R., and Roberts, B.: Ducted compressional waves in the magnetosphere in the double-polytropic approximation, Ann. Geophys., 20, 1553-1558,, 2002.

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