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Sunspot seismology: accounting for magnetohydrodynamic wave processes using imaging spectropolarimetry

The effects of acoustic wave absorption, mode conversion and transmission by a sunspot on the helioseismic inferences are widely discussed, but yet accounting for them has proved difficult 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 A) and insensitive (Fe I 7090 A) 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.