Forward Modeling Helioseismic Signatures of One- and Two-cell Meridional Circulation

TL;DR

This study models helioseismic signatures of different meridional circulation patterns in the Sun using 3D simulations, revealing current observational techniques' potential and limitations in distinguishing circulation structures.

Contribution

It introduces a 3D linear Euler solver to simulate helioseismic signals for various meridional circulation models, assessing observational capabilities.

Findings

Current helioseismology can provide insights into flow location and strength.

Distinguishing between single-cell and double-cell circulation profiles remains challenging.

Simulations suggest potential for improved interpretation of solar interior flows.

Abstract

Using a 3D global solver of the linearized Euler equations, we model acoustic oscillations over background velocity flow fields of single-cell meridional circulation with deep and shallow return flows as well as double-cell meridional circulation with strong and weak reversals. The velocities are generated using a mean-field hydrodynamic and dynamo model -- moving through the regimes with minimal parameter changes; counter-rotation near the base of the tachocline is induced by sign inversion of the non-diffusive action of turbulent Reynolds stresses ($\Lambda$-effect) due to the radial inhomogeneity of the Coriolis number. By mimicking the stochastic excitation of resonant modes in the convective interior, we simulate realization noise present in solar observations. Using deep-focusing to analyze differences in travel-time signatures between the four regimes, as well as comparing to solar observations, we show that current helioseismology techniques may offer important insights about the location and strength of the return flow, however, that it may not currently be possible to definitively distinguish between profiles of single-cell or double-cell meridional circulation.