Resonant phenomena of hydromagnetic waves in non-uniform space plasmas

Abstract

In non-uniform plasmas, linear magnetohydrodynamic waves can get into resonant interaction with the background plasma at locations where propagating waves and local modes, existing in regions of pronounced non-uniformity, satisfy the resonant condition of phase synchronism. This leads to a resonant excitation of local modes and growth of their amplitudes. Consequently, the effect of dissipation becomes important which eventually limits the amplitudes to finite values in domains of around resonances. The incident wave then loses its energy and a process known as the resonant wave absorption occurs. In a non-static background plasma, a non-uniform macroscopic mass flow can act as a free energy source, causing phenomena of resonant instability of local modes and over-reflection of incident waves when reflected waves gain energy from the flow. Such resonant processes may appear in magnetic structures in the solar corona, in sunspots, in planetary magnetopauses, bowshocks and magnetotails contributing to energy transfer and transports of other physical quantities. Some of these phenomena can be related to locally enhanced physical quantities as detected by satellites. In this paper, we present a number of analytical and computational approaches in treating the resonant wave behaviour in non-uniform plasma configurations relevant to solar and terrestrial conditions.