Separating surface magnetic effects in sunspot seismology: new time-distance helioseismic diagnostics

TL;DR

This paper introduces new time-distance helioseismic diagnostics that effectively separate surface magnetic effects from deeper perturbations in sunspot seismology, enhancing understanding of subsurface structures.

Contribution

It presents novel measurement techniques that distinguish surface magnetic influences from deeper perturbations using surface- and deep-focus geometries in helioseismology.

Findings

Detected increased wave speed extending to 18 Mm beneath sunspots.

Identified wave absorption and conversion signatures related to surface magnetic effects.

Demonstrated that travel time variations are due to surface phenomena rather than shallow perturbations.

Abstract

Time-distance helioseismic measurements in surface- and deep-focus geometries for wave-paths that distinguish surface magnetic contributions from those due to deeper perturbations beneath a large sunspot are presented and analysed. Travel times showing an increased wave speed region extending down to about 18 Mm beneath the spot are detected in deep-focus geometry that largely avoids use of wave field within the spot. Direction (in- or out-going wave) and surface magnetic field (or focus depth) dependent changes in frequency dependence of travel times are shown and identified to be signatures of wave absorption and conversion in near surface layers rather than that of shallowness of sunspot induced perturbations.