Dynamics of circularly polarised Alfvén waves in a stratified medium

Chalmers University of Technology/Göteborg University, Department of Astronomy & Astrophysics, 412 96 Gothenburg, Sweden e-mail: r.turkmani@ic.ac.uk

Received: 10 April 2004
Accepted: 9 August 2004

Abstract

We present a numerical study of the propagation of circularly polarised Alfvén waves in a plane-parallel stratified medium. Because of the stratification there is a global gradient in the magnetic pressure of the wave, which accelerates the plasma and supports it against gravity. The spatial distribution of the wave force is determined by the amplitude of the Alfvén wave which in its turn is set by the influences of dissipation, reflection and parametric decay on the wave. The Alfvén wave is partially reflected off the smooth density gradient. The relative amplitude of the reflected wave is proportional to the background magnetic field strength and is independent of the absolute amplitude of the wave. At high amplitudes strong backward propagating Alfvén waves are generated through the parametric decay of the Alfvén wave, and by reflection off density fluctuations generated by the wave front.