On the hydrostatic stratification of the solar tachocline

TL;DR

This paper investigates the solar tachocline's structure by combining opacity adjustments and a diffusion-based material mixing model to reconcile observed sound speed anomalies with solar models.

Contribution

It introduces a novel combination of opacity modification and density-dependent diffusion to address the tachocline glitch in solar models.

Findings

Opacity modification alone is insufficient.

A density-dependent diffusion combined with opacity adjustment effectively removes the tachocline glitch.

The resulting model aligns well with helioseismic observations.

Abstract

We present an attempt to reconcile the solar tachocline glitch, a thin layer immediately beneath the convection zone in which the seismically inferred sound speed in the Sun exceeds corresponding values in standard solar models, with a degree of partial material mixing which we presume to have resulted from a combination of convective overshoot, wave transport and tachocline circulation. We first summarize the effects of either modifying in the models the opacity in the radiative interior or of incorporating either slow or fast tachocline circulation. Neither alone is successful. We then consider, without physical justification, incomplete material redistribution immediately beneath the convection zone which is slow enough not to disturb radiative equilibrium. It is modelled simply as a diffusion process. We find that, in combination with an appropriate opacity modification, it is possible to find a density-dependent diffusion coefficient that removes the glitch almost entirely, with a radiative envelope that is consistent with seismology.