Helioseismic Holography of Simulated Solar Convection and Prospects for the Detection of Small-Scale Subsurface Flows

TL;DR

This study validates helioseismic holography using realistic solar convection simulations, showing its effectiveness in detecting subsurface flows near the surface but limitations at greater depths and shorter timescales.

Contribution

It demonstrates the accuracy of helioseismic holography in modeling subsurface flows and clarifies its depth and temporal detection limits using realistic simulations.

Findings

Reasonable agreement between observed and modeled travel times.

Detection of small-scale flows is limited to about 5 Mm depth.

Most signal originates within 2 Mm below the surface.

Abstract

We perform helioseismic holography on realistic solar convection simulations and compare the observed travel-time perturbations with the expected travel times from the horizontal flows in the simulations computed from forward models under the assumption of the Born approximation. We demonstrate reasonable agreement between the observed and model travel times which reinforces the validity of helioseismic holography in the detection of subsurface horizontal flows. From the variation of the signal-to-noise ratio with depth, we conclude that the helioseismic detection of individual flow structures with spatial scales of supergranulation or smaller is not possible for depths below about 5 Mm below the surface over time scales less than a day. Approximately half of the observed signal originates within the first 2 Mm below the surface. A consequence of this is a rapid decrease (and reversal in some cases) of the travel-time perturbations with depth due to the contribution to the measurements of oppositely directed surface flows in neighboring convective cells. This confirms an earlier interpretation of similar effects reported from observations.