Global effects of local sound-speed perturbations in the Sun: A theoretical study

TL;DR

This theoretical study investigates how localized sound-speed changes in the Sun affect global helioseismic modes, revealing sensitivities and subtle signatures of thermal asphericities through advanced numerical simulations.

Contribution

It extends realization noise subtraction techniques to global modes, enabling high-resolution detection of sound-speed perturbation effects in the Sun.

Findings

Global modes are twice as sensitive to perturbations near the convection zone bottom.

Slight lifting of m-degeneracy observed in a coefficients.

Modes near perturbations show small amplitude shifts (~0.5%).

Abstract

We study the effect of localized sound-speed perturbations on global mode frequencies by applying techniques of global helioseismology on numerical simulations of the solar acoustic wave field. Extending the method of realization noise subtraction (e.g. Hanasoge et al. 2007) to global modes and exploiting the luxury of full spherical coverage, we are able to achieve very highly resolved frequency differences that are used to study sensitivities and the signatures of the thermal asphericities. We find that (1) global modes are almost twice as sensitive to sound-speed perturbations at the bottom of the convection zone as in comparison to anomalies well in the radiative interior ($r\lesssim0.55 R_\odot$), (2) the $m$-degeneracy is lifted ever so slightly, as seen in the $a$ coefficients, and (3) modes that propagate in the vicinity of the perturbations show small amplitude shifts ($\sim 0.5%$).