Amplitude modulation of solar p-modes by surface magnetic fields
Applied Mathematics Department, University of Sheffield, Sheffield, S3 7RH, UK e-mail: R.Jain@sheffield.ac.uk
2 School of Mathematics, University of Manchester, Manchester, UK
Accepted: 9 July 2007
Context.It is known from Doppler velocity measurements that the amplitudes of solar p-modes are modulated by strong photospheric magnetic field.
Aims.The aim of this paper is to investigate amplitude modulation by model surface magnetic fields.
Methods.Linearised magnetohydrodynamics equations, in the absence of gravity, are used to derive the inhomogeneous wave equation which is then solved using the Born Approximation.
Results.The amount of modulation depends on the plasma beta, the distance from the magnetic region and the wavenumber. It is also found that the direction of observation could also have an effect on the amount of modulation. Finally, the applicability of the findings to the observational data suggests that the modulation depends on the properties of the magnetic field region and measuring it is an un-contaminating probe for the magnetic field.
Key words: Sun: magnetic fields / Sun: oscillations / magnetohydrodynamics (MHD) / Sun: helioseismology
© ESO, 2007