Probing sunspots with two-skip time-distance helioseismology

TL;DR

This paper develops a helioseismology technique that isolates the structural properties of sunspots by using two-skip waves, which are insensitive to magnetic effects, enabling clearer insights into sunspot structure.

Contribution

The study introduces a method using two-skip time-distance helioseismology to separate magnetic effects from structural properties in sunspot analysis.

Findings

Large travel time differences observed for sunspots.

Two-skip waves are insensitive to magnetic fields.

Potential for improved sunspot structural modeling.

Abstract

Previous helioseismology of sunspots has been sensitive to both the structural and magnetic aspects of sunspot structure. We aim to develop a technique that is insensitive to the magnetic component so the two aspects can be more readily separated. We study waves reflected almost vertically from the underside of a sunspot. Time-distance helioseismology was used to measure travel times for the waves. Ray theory and a detailed sunspot model were used to calculate travel times for comparison. It is shown that these large distance waves are insensitive to the magnetic field in the sunspot. The largest travel time differences for any solar phenomena are observed. With sufficient modeling effort, these should lead to better understanding of sunspot structure.