Abstract:
E ects of acoustic wave absorption, mode conversion and transmission
by a sunspot on the helioseismic inferences are widely discussed,
yet accounting for them has proved di cult for lack of a consistent framework
within helioseismic modelling. Here, following a discussion of problems
and issues that the near-surface magnetohydrodynamics hosts through
a complex interplay of radiative transfer, measurement issues, and MHD
wave processes, I present some possibilities entirely from observational
analyses based on imaging spectropolarimetry. In particular, I present some
results on wave evolution as a function of observation height and inclination
of magnetic field to the vertical, derived from a high-cadence imaging
spectropolarimetric observation of a sunspot and its surroundings using the
instrument IBIS (NSO/Sac Peak, USA). These observations were made in
magnetically sensitive (Fe I 6173 Å) and insensitive (Fe I 7090 Å) upper
photospheric absorption lines. Wave travel time contributions from within
the photospheric layers of a sunspot estimated here would then need to be
removed from the inversion modelling procedure, that does not have the
provision to account for them.
