Basic MHD dynamics

Abstract

This Chapter is concerned with the dynamics of magnetized plasmas in the very-low-frequency large-scale approximation of Magnetohydrodynamics. The focus is on the basic MHD waves that can occur in a magnetized plasma. We forget about the gravitational force and are concerned with the MHD waves that are driven by the plasma pressure force and the Lorentz force. This leads us to Alfvén waves and magnetosonic waves. The study of these waves enable us to identify the Alfvén velocity, v _A , and the velocity of sound, v _s , as fundamental quantities characterizing the very-low-frequency large-scale fluid-like behaviour of plasmas. Magneto-gravity waves will be absent for the present discussion. There are situations in solar and astrophysical plasmas where a gravitational force, either due to an external gravitational field or due to self-gravitation, has to be included in the mathematical analysis.