High Resolution Helioseismic Imaging of Subsurface Structures and Flows of A Solar Active Region Observed by Hinode

TL;DR

This study uses high-resolution Hinode observations to perform time-distance helioseismology, revealing detailed subsurface structures and flows beneath a solar active region, including sunspot dynamics and mesoscale convection.

Contribution

It demonstrates the capability of Hinode data for high-resolution helioseismic imaging and compares filtering effects, advancing understanding of sunspot subsurface structures.

Findings

Subsurface wave-speed structures similar to previous SOHO/MDI results.

Clear resolution of downward flows and mass circulations around sunspots.

Detection of mesoscale convective motions beneath sunspots.

Abstract

We analyze a solar active region observed by the Hinode CaII H line using the time-distance helioseismology technique, and infer wave-speed perturbation structures and flow fields beneath the active region with a high spatial resolution. The general subsurface wave-speed structure is similar to the previous results obtained from SOHO/MDI observations. The general subsurface flow structure is also similar, and the downward flows beneath the sunspot and the mass circulations around the sunspot are clearly resolved. Below the sunspot, some organized divergent flow cells are observed, and these structures may indicate the existence of mesoscale convective motions. Near the light bridge inside the sunspot, hotter plasma is found beneath, and flows divergent from this area are observed. The Hinode data also allow us to investigate potential uncertainties caused by the use of phase-speed filter for short travel distances. Comparing the measurements with and without the phase-speed filtering, we find out that inside the sunspot, mean acoustic travel times are in basic agreement, but the values are underestimated by a factor of 20-40% inside the sunspot umbra for measurements with the filtering. The initial acoustic tomography results from Hinode show a great potential of using high-resolution observations for probing the internal structure and dynamics of sunspots.