Poster abstract

Guided waves at spherical interfaces in the solar atmosphere
I. Ballai and E. Forgacs-Dajka


Geometrical restriction of MHD wave ropagation in solar magnetic structures is known to confer a dispersive character for waves. Waves
propagating along discontinuities in the medium are known to remain localized. As an extension to theories of guided waves in magnetic slabs and cylinders under solar and stellar conditions, we study the propagation of magnetoacoustic-gravity waves at a spherical interface in the low solar corona (considered here by a density discontinuity), modelling global waves recently observed in the corona in EUV wavelengths. Using conservation laws at the interface, we derive the dispersion relation in spherical geometry with a radially expanding magnetic field in the presence of gravitational stratification using an approximative method taking into account that propagation takes place near the solar surface. The frequency of waves is shown to increase with decreasing density contrast at the interface. We also show that for a given azimuthal wavenumber the magnetic field has a very small effect on the value of the frequency of waves. When plotted against the location of the interface (in the radial direction) the frequency varies inversely proportional with the distance, hile for a fixed density ratio and location of the interface the frequency is obtained to be defined in a very narrow region.