The Sun's meridional circulation and interior magnetic field

TL;DR

This paper presents an analytical model of the solar interior that explains how meridional flows can confine magnetic fields, addressing limitations of previous numerical simulations in reproducing the solar tachocline's properties.

Contribution

It introduces a simple analytical magneto-hydrodynamic model identifying parameter regimes where meridional flows confine magnetic fields, guiding future numerical simulations.

Findings

Meridional flows can confine magnetic fields at realistic solar parameters.

Existing numerical simulations underestimate meridional flow strength.

The model aligns with the Gough & McIntyre tachocline theory.

Abstract

To date, no self-consistent numerical simulation of the solar interior has succeeded in reproducing the observed thinness of the solar tachocline, and the persistence of uniform rotation beneath it. Although it is known that the uniform rotation can be explained by the presence of a global-scale confined magnetic field, numerical simulations have thus far failed to produce any solution where such a field remains confined against outward diffusion. We argue that the problem lies in the choice of parameters for which these numerical simulations have been performed. We construct a simple analytical magneto-hydrodynamic model of the solar interior and identify several distinct parameter regimes. For realistic solar parameter values, our results are in broad agreement with the tachocline model of Gough & McIntyre. In this regime, meridional flows driven at the base of the convection zone are of sufficient amplitude to hold back the interior magnetic field against diffusion. For the parameter values used in existing numerical simulations, on the other hand, we find that meridional flows are significantly weaker and, we argue, unable to confine the interior field. We propose a method for selecting parameter values in future numerical models.