The Solar f-Mode as an Interfacial Mode at the Chromosphere-Corona Transition
Abstract
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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 1994
- DOI:
- 10.1086/173826
- Bibcode:
- 1994ApJ...423..488R
- Keywords:
-
- Chromosphere;
- Solar Corona;
- Solar Transition Region;
- Spherical Harmonics;
- Stellar Models;
- Density Distribution;
- Energy Spectra;
- Solar Oscillations;
- Wave Propagation;
- Astrophysics;
- SUN: ATMOSPHERE;
- SUN: OSCILLATIONS;
- SUN: TRANSITION REGION