Helioseismic detection of deep meridional flow

TL;DR

This paper proposes a helioseismic method to detect deep meridional flows in the solar convection zone by analyzing wave eigenfunction distortions and phase variations, overcoming limitations of frequency-based techniques.

Contribution

It introduces a novel approach to infer deep solar meridional flows using spatial phase distortions of helioseismic waves, extending beyond traditional frequency shift methods.

Findings

Potential to detect deep meridional flow in the solar interior.

Method demonstrated with a simple toy model.

Suggests feasibility of inferring subsurface flows from phase variations.

Abstract

Steady meridional flow makes no first-order perturbation to the frequencies of helioseismic normal modes. It does, however, Doppler shift the local wavenumber, thereby distorting the eigenfunctions. For high-degree modes, whose peaks in a power spectrum are blended into continuous ridges, the effect of the distortion is to shift the locations of those ridges. From this blended superposition of modes, one can isolate oppositely directed wave components with the same local horizontal wavenumber and measure a frequency difference which can be safely used to infer the subsurface background flow. But such a procedure fails for the components of the more-deeply-penetrating low-degree modes that are not blended into ridges. Instead, one must analyze the spatial distortions explicitly. With a simple toy model, we illustrate one method by which that might be accomplished by measuring the spatial variation of the oscillation phase. We estimate that by this procedure it might be possible to infer meridional flow deep in the solar convection zone.