Tomography of plasma flows in the upper solar convection zone using time--distance inversion combining ridge and phase-speed filtering

TL;DR

This study compares two helioseismic filtering methods for plasma flow inversion in the solar convection zone, demonstrating that their combination enhances inversion accuracy and reveals flow structure variations with depth.

Contribution

It introduces a combined inversion approach using ridge and phase-speed filtering, improving flow estimates and depth-dependent flow structure analysis in the solar convection zone.

Findings

Both filtering methods yield similar flow estimates with proper kernels.

Combining methods improves inversion quality, reducing noise and sharpening averaging kernels.

Flow coherence is limited to upper ~5 Mm, with larger structures at greater depths.

Abstract

The consistency of time--distance inversions for horizontal components of the plasma flow on supergranular scales in the upper solar convection zone is checked by comparing the results derived using two k--\omega filtering procedures -- ridge filtering and phase-speed filtering -- commonly used in time--distance helioseismology. It is shown that both approaches result in similar flow estimates when finite-frequency sensitivity kernels are used. It is further demonstrated that the performance of the inversion improves (in terms of simultaneously better averaging kernel and lower noise level) when the two approaches are combined together in one inversion. Using the combined inversion I invert for horizontal flows in the upper 10 Mm of the solar convection zone. The flows connected with supergranulation seem to be coherent only in the upper ~5 Mm depth, deeper down there is a hint on change of convection scales towards structures larger than supergranules.