Seismic Constraints on Interior Solar Convection

TL;DR

This study uses local helioseismology to place upper limits on the velocity and scale of large-scale solar convective cells at different depths, revealing weak flows near the surface and challenges in imaging deeper convection.

Contribution

It introduces a calibration method linking helioseismic wave sensitivity to convective velocities using simulations, providing new constraints on solar interior convection.

Findings

Convective velocities at 0.95 solar radii are less than 15 m/s for scales with spherical harmonic degree <20.

Helioseismic waves have decreasing sensitivity to deeper convective features.

Surface convective flows are weak and difficult to detect at greater depths.

Abstract

We constrain the velocity spectral distribution of global-scale solar convective cells at depth using techniques of local helioseismology. We calibrate the sensitivity of helioseismic waves to large-scale convective cells in the interior by analyzing simulations of waves propagating through a velocity snapshot of global solar convection via methods of time-distance helioseismology. Applying identical analysis techniques to observations of the Sun, we are able to bound from above the magnitudes of solar convective cells as a function of spatial convective scale. We find that convection at a depth of $r/R_\odot = 0.95$ with spatial extent $\ell <20$, where $\ell$ is the spherical harmonic degree, comprise weak flow systems, on the order of 15 m/s or less. Convective features deeper than $r/R_\odot = 0.95$ are more difficult to image due to the rapidly decreasing sensitivity of helioseismic waves.