Sunspot seismology: accounting for magnetohydrodynamic wave processes using imaging spectropolarimetry

TL;DR

This paper investigates how magnetohydrodynamic wave processes affect sunspot seismology by analyzing high-cadence imaging spectropolarimetric data to improve helioseismic inferences near sunspots.

Contribution

It introduces observational analysis methods to account for MHD wave effects in sunspot helioseismology, addressing a gap in modeling approaches.

Findings

Wave evolution varies with observation height and magnetic inclination.

Wave travel time contributions from sunspot layers can be estimated.

Results highlight the need to incorporate these effects into inversion models.

Abstract

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.