Mode coupling in the solar corona

Previous discussions of mode coupling at a QT region have assumed vertical incidence and have hus invoked magnetic structures which violate div B = o. A new method is developed here for alculating the coupling coefficients for oblique incidence so that coupling at a QT region can be reated without invoking nonphysical magnetic structures. The method involves solving the Booker uartic equation implicitly in terms of the familiar formulae of magnetoionic theory. A coupling pproximation is introduced which involves one step in an iterative procedure to find explicit solutions rom the implicit ones. The approximation is necessarily valid in a finite range about the critical oupling points. The present method is used to generalize the results of Cohen to allow oblique ncidence. The results of the existing discussions of mode coupling for vertical incidence and nonphysical agnetic structures can be justified both qualitatively and semiquantitatively (although ith a slightly different physical interpretation).