Local helioseismic and spectroscopic analyses of interactions between acoustic waves and a sunspot

TL;DR

This study uses high-resolution spectropolarimetric data to analyze how magnetic field inclination affects acoustic wave transmission in sunspots, revealing impacts on helioseismic travel times and evidence of subsurface wave sources.

Contribution

It provides new insights into magnetic inclination effects on wave transmission and demonstrates how different spectral lines influence helioseismic travel time measurements.

Findings

Magnetic inclination angle affects wave transmission into upward propagating waves.

Helioseismic travel times are influenced by wave direction, causing potential errors in flow measurements.

Evidence of acoustic wave sources beneath the sunspot's umbral photosphere.

Abstract

Using a high cadence imaging spectropolarimetric observation of a sunspot and its surroundings in magnetically sensitive (FeI 6173 A) and insensitive (FeI 7090 A) upper photospheric absorption lines, we map the instantaneous wave phases and helioseismic travel times as a function of observation height and inclination of magnetic field to the vertical. We confirm the magnetic inclination angle dependent transmission of incident acoustic waves into upward propagating waves, and derive (1) proof that helioseismic travel times receive direction dependent contributions from such waves and hence cause errors in conventional flow inferences, (2) evidences for acoustic wave sources beneath the umbral photosphere, and (3) significant differences in travel times measured from the chosen magnetically sensitive and insensitive spectral lines.