Angular scattering of radio waves: Implications for mode coupling in the solar corona

The solar corona is highly inhomogeneous. The magnetionic modes may therefore couple under certain circumstances, and the polarization properties of solar radio sources may, as a consequence, be modified. An application of the simple theory of mode coupling to the propagation of radio waves in the solar corona leads to the expectation that mode coupling in quasi-transverse (QT) magnetic field regions should always be weak (coupling ratio Q much less than 1) at meter wavelengths. Observations to date suggest that, on the contrary, mode coupling is moderate (Q approximately 1) to strong (Q much greater than 1) in QT regions at meter wavelengths. I suggest that observations and theory can be reconciled by including the effect of turbulence on mode coupling. Specifically, angular scattering on turbulent inhomogeneities greatly reduces the spatial scale relevant to the theory at low frequencies. As a result, the coupling ratio is increased by a corresponding factor and mode coupling may be moderate to strong in QT regions at meter wavelengths.