Wave processes in the solar upper atmosphere
Abstract
The existence of a wide variety of wave-like phenomena are inferred from observations of the solar upper atmosphere. Acoustic waves play an important role for the dynamics and energetics of the chromosphere but additional heating seems necessary even for the internetwork regions. We show that it is unlikely that this extra heating is due to high frequency acoustic waves due to the lack of their preferential excitation and the strong radiative damping of high frequency waves in the photosphere. When acoustic waves reach the height where the magnetic pressure equals the gas pressure they will undergo mode conversion, refraction and reflection. We discuss these processes and show that the critical quantity is the angle between the magnetic field and the velocity polarization; at angles smaller than 30 degrees much of the acoustic, fast mode from the photosphere is transmitted as an acoustic, slow mode propagating along the field lines. At larger angles, most of the energy is refracted/reflected and returns as a fast mode creating an interference pattern between the upward and downward propagating waves. In 3D, this interference between waves at small angles creates patterns with large horizontal phase speeds, especially close to magnetic field concentrations. When damping from shock dissipation and radiation is taken into account, the waves in the low-mid chromosphere have mostly the character of upward propagating acoustic waves and it is only close to the reflecting layer we get similar amplitudes for the upward propagating and refracted/reflected waves.
- Publication:
-
SOLMAG 2002. Proceedings of the Magnetic Coupling of the Solar Atmosphere Euroconference
- Pub Date:
- October 2002
- Bibcode:
- 2002ESASP.505..293C
- Keywords:
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- Sun;
- Chromosphere;
- Oscillations;
- Waves