3D Helioseismic Forward-Modeling and Analysis of Meridional Circulation

The 3D Global Acoustic Linearized Euler (GALE) code is used to explore the variance in helioseismic signatures that result from various profiles of meridional circulation. The structure of meridional circulation regulates the redistribution of angular momentum and magnetic flux that governs the solar cycle. Forward-modeling is a useful tool in exploring the structure of meridional circulation and its impact on global parameters and can help resolve the current controversy between single and double-cell circulation profiles. Profiles of meridional circulation are generated using mean-field dynamo models, which induce a reverse flow near the base of the convection zone, characteristic of double-cell meridional circulation, with the inclusion of turbulent pumping (-effect) resulting from a strong rotational gradient in the region. These models provide physics-based mechanisms for the low-end in potential differences between single- and double-cell meridional circulation profiles. The resulting flows are used as background velocities in the linearized acoustic GALE codesimulating the stochastic excitation of acoustic perturbations. Techniques in local helioseismology are then applied to measure flow signatures, showing that within the observational time-period of the HMI instrument onboard Solar Dynamics Observatory, it may not be possible to definitively distinguish between single-cell and double-cell meridional circulation structure. This analysis is extended to models of meridional circulation generated in convectively-driven non-linear 3D global-Sun simulations to explore the helioseismic differences generated by these models and compare them with observations.