Photospheric high-frequency acoustic power excess in sunspot umbra: signature of magneto-acoustic modes
- 1Department of Physics and Mathematics, University of Hull, Cottingham Road, Kingston-upon-Hull, HU6 7RX, UK
- 2Monash Centre for Astrophysics, School of Mathematical Sciences, Monash University, Clayton, Victoria, 3800, Australia
- 3Dept of Automatic Control and Systems Engineering, The University of Sheffield, Mappin Street, Sheffield, S1 3JD, UK
- 4SP2RC, School of Mathematics and Statistics, Univ. of Sheffield, Hounsfield Road, Hicks Building, Sheffield, S3 7RH, UK
- 5High Altitude Observatory, P.O. Box 3000, Boulder, CO 80307-3000, USA
Abstract. We present observational evidence for the presence of MHD (magnetohydrodynamic) waves in the solar photosphere deduced from SOHO/MDI (Solar and Heliospheric Observatory/Michelson Doppler Imager) Dopplergram velocity observations. The magneto-acoustic perturbations are observed as acoustic power enhancement in the sunspot umbra at high-frequency bands in the velocity component perpendicular to the magnetic field. We use numerical modelling of wave propagation through localised non-uniform magnetic field concentration along with the same filtering procedure as applied to the observations to identify the observed waves. Guided by the results of the numerical simulations we classify the observed oscillations as magneto-acoustic waves excited by the trapped sub-photospheric acoustic waves. We consider the potential application of the presented method as a diagnostic tool for magnetohelioseismology.