Abstract
The linearized theory for the parallel propagation of magnetoacoustic-gravity surface waves is developed and a dispersion relation obtained for the case of an isothermal interface of a uniform horizontal magnetic field residing above a field-free medium. The transcendental dispersion relation is solved numerically for a range of parameters and the resulting dispersion curves and corresponding eigenfunctions plotted. As in the case of a uniform Alfvén speed (Paper I), the existence of the fast and slow magnetoacoustic-gravity surface modes and the f-mode (modified by the presence of the uniform magnetic field) is determined by the relative temperatures of the two media either side of the interface. If the lower field-free region is cooler than the upper magnetic atmosphere only the slow magnetoacoustic-gravity surface mode may propagate. In addition to these three surface modes we find higher harmonic-type trapped modes. The existence of these modes also depends on the temperatures either side of the interface. They propagate only when both the field-free region is warmer than the magnetic field region and the Alfvén speed is greater than the corresponding sound speed in the magnetic atmosphere.
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Miles, A.J., Allen, H.R. & Roberts, B. Magnetoacoustic-gravity surface waves. Sol Phys 141, 235–251 (1992). https://doi.org/10.1007/BF00155177
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DOI: https://doi.org/10.1007/BF00155177