Solar -modes and surface magnetic fields: Is there an acoustic emission?

MDI/SOHO observations

¹ Department of Physics, UMIST, Manchester M60 1QD, UK e-mail: rjain@suraj.phy.umist.ac.uk
² JILA, University of Colorado, Boulder, CO 80309-440, USA e-mail: dhaber@solarz.colorado.edu

Corresponding author: R. Jain, rjain@suraj.phy.umist.ac.uk

Received: 18 July 2001
Accepted: 28 February 2002

Abstract

We study the effect of magnetism on the surface amplitude of p-modes by creating power maps using Doppler velocity, line-depth and continuum intensity data taken by the Michelson Doppler Interferometer (MDI) instrument on board SOHO. This analysis, using proper tracking procedures, of MDI line-depth data and its comparison with the simultaneous Doppler velocity data is the first such analysis. All three datasets show that the p-mode power is suppressed in the magnetic region with suppression increasing with field strength. However, in the high-frequency range, the power is enhanced in the Doppler velocity and line-depth data but not in continuum intensity. This enhancement, when present, appears to be in intermediate field strength elements in the immediate vicinity of a magnetically active region.