Magnetoatmospheric Oscillations in Flux tubes

Dipankar Banerjee

Armagh Observatory, Armagh, College Hill, BT619DG, N.Ireland

Abstract: The present investigation is a continuation of earlier work by Hasan \& Christensen-Dalsgaard (1992) and Banerjee, Hasan \& Christensen-Dalsgaard (1995), who has examined the effects of a weak vertical magnetic field on the normal adiabatic modes of an isothermal atmosphere by combining a semi-analytic approach, based on asymptotic dispersion relations, with numerical solutions. In the present study of the strong-field case, we concentrate on the behaviour of the modes near the avoided crossings in the $k - \omega$ diagram for zero gradient boundary conditions. It was predicted that due to strong mode coupling the eigenfrequencies in these regions become complex. We present here the consequences of mode coupling in such regions, which could be relevant for sunspots and more generally for stratified flux tubes.