The 3-min oscillations of the solar chromosphere - A basic physical effect?
Abstract
The resonant excitation of the acoustic cut-off frequency mode in a stratified atmosphere, an affect which provides a simple explanation of the observed 3-min oscillations of the solar chromosphere, is discussed. It is demonstrated that the cut-off frequency mode is excited also by long period disturbances, which, in the case of the sun, could be the wave trains of the photospheric 5-min oscillations. Due to the spatial attenuation of the evanescent waves, the oscillations at the cut-off frequency dominate the oscillatory signal above a certain height (about 6 to 8 scale heights above the moving piston). The oscillations at the cut-off frequency are very persistent and vanish for t approaches infinity only in an infinitely extended atmosphere without any reflecting boundaries. In a finite atmosphere with an upper boundary at which total or partial reflection occurs, the Omega = 1 oscillations are permanently excited. It is concluded that there is no need for a chromospheric cavity to explain the observed chromospheric 3-min resonance, as was previously assumed.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- October 1991
- Bibcode:
- 1991A&A...250..235F
- Keywords:
-
- Chromosphere;
- Solar Oscillations;
- Solar Physics;
- Hydrodynamics;
- Solar Cycles;
- Solar Physics