MHD waves on the Sun

Abstract

Theoretical aspects of wave propagation in an atmosphere with a vertical magnetic field are reviewed. Starting from the ideal magneto hydrodynamic equations. The differential equations governing linear oscillations presented for stratified medium with a vertical magnetic field. In order to obtain physical insight into the nature of the different types of waves; it is instructive to first consider certain simple cases, for which the wave equation can be solved analytically. The dispersion relations for these modes are examined. Next the case of an isothermal stratified atmosphere is considered in the limit of strong and weak magnetic fields. The effect of magnetic fields on the model structure is highlighted. Coupling of different types of modes is examined. Solutions for general case Corresponding to the atmosphere in the umbra of a sunspot are also presented and related to observations of umbral oscillations. Finally, wave propagation in intense flux tubes is briefly discussed.