Acoustic oscillations in a field-free cavity under solar small-scale bipolar magnetic canopy
- 1Georgian National Astrophysical Observatory (Abastumani Astrophysical Observatory), Al. Kazbegi ave. 2a, 0160 Tbilisi, Georgia
- 2Institute for Theoretical Physics, K.U. Leuven, Celestijnenlaan 200 D, 3001, Leuven, Belgium
- 3Center for Plasma Astrophysics, K.U.Leuven, 200 B, 3001, Leuven, Belgium
Abstract. Observations show the increase of high-frequency wave power near magnetic network cores and active regions in the solar lower atmosphere. This phenomenon can be explained by the interaction of acoustic waves with a magnetic field. We consider small-scale, bipolar, magnetic field canopy structure near the network cores and active regions overlying field-free cylindrical cavities of the photosphere. Solving the plasma equations we get the analytical dispersion relation of acoustic oscillations in the field-free cavity area. We found that the m=1 mode, where m is azimuthal wave number, cannot be trapped under the canopy due to energy leakage upwards. However, higher (m≥2) harmonics can be easily trapped leading to the observed acoustic power halos under the canopy.