One-sided arc averaging geometries in time-distance local helioseismology

TL;DR

This paper introduces a novel helioseismic methodology using one-sided arc averaging geometries to better analyze active solar regions affected by magnetic fields, improving the measurement of plasma properties near sunspots.

Contribution

The authors develop and validate a new non-linear travel-time measurement approach with one-sided arc averaging geometries for helioseismology, enhancing analysis near active regions.

Findings

Successfully reconstructed annulus travel times in quiet Sun regions.

Inverted surface horizontal flows in sunspots are consistent with other methods.

Method suppresses magnetic effects up to the outer penumbra.

Abstract

The study of solar oscillations (helioseismology) has been a very successful method of researching the Sun. Helioseismology teaches us about the structure and mean properties of the Sun. Together with mid-resolution data, the local properties were uncovered in quiet-Sun regions. However, magnetic fields affect the oscillations and prevent us from studying the properties of magnetically active regions with helioseismology. We aim to create a new methodology to suppress the negative effects of magnetic fields on solar oscillations and measure plasma properties close to active regions. The methodology consists of new averaging geometries, a non-linear approach to travel-time measurements, and a consistent inversion method that combines plasma flows and sound-speed perturbations. We constructed the one-sided arc averaging geometries and applied them to the non-linear approach of travel-time measurements. Using the one-sided arc travel times, we reconstructed the annulus travel times in a quiet-Sun region. We tested the methodology against the validated helioseismic inversion pipeline. We applied the new methodology for an inversion for surface horizontal flows in a region with a circular H-type sunspot. The inverted surface horizontal flows are comparable with the output of the coherent structure tracking, which is not strongly affected by the presence of the magnetic field. We show that the new methodology suppresses the negative effects of magnetic fields up to outer penumbra. We measure divergent flows with properties comparable to the moat flow. The new methodology can teach us about the depth structure of active regions and physical conditions that contribute to the evolution of the active regions.