Observations of the solar f-mode at intermediate and high spherical harmonic degree show substantial departures from the dispersion relation expected for a pure surface gravity oscillation. We suggest that the waves are reflected by the high density gradient in the region of the chromosphere-corona transition and are therefore characterized better as interfacial modes localized near the transition. An analytical calculation, for a simple model in which the transition is treated as a discontinuity, shows that such modes have a dispersion relation with the correct qualitative features to explain the observations. However, quantitative agreement is not possible for reasonable parameter values. We next consider a more general atmospheric structure with a continuous stratification for which asymptotic frequency estimates are obtained. These are compared with direct numerical solutions of the differential equations. The frequencies are found to give a much closer quantitative agreement with the observations. We suggest that f-mode seismology might be used to obtain direct information about the average structure of the solar atmosphere and transition region.
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Rosenthal et al. (1994) studied this question.