ABSTRACT
This chapter presents a relatively simple, yet very useful, model for the dynamics of fully ionized plasmas, as they are found in, for instance, the Earth’s upper ionosphere, in the magnetosphere or in the more distant regions of space. The model is based on some simple assumptions, by arguing that a plasma can be considered as a medium which follows the same basic laws as any other continuum, i.e., the equation of continuity and Newton’s second law. In principle, in its basic form Magneto-Hydro-Dynamics (MHD) applies not only for plasmas but liquid metallic conductors (like Mercury) as well. In practice the resistivity of the metals is found to be a problem and the equivalent of the plasma parameter is small, but early experiments on the basic properties of the MHD model were performed in such liquid metals, studies of wave propagation in particular.
