What Prevents Internal Gravity Waves From Disturbing the Solar Uniform Rotation?

TL;DR

This paper investigates why internal gravity waves (IGWs) do not disrupt the Sun's nearly uniform rotation, highlighting the need for magnetic processes and molecular weight gradients to maintain this uniformity.

Contribution

It demonstrates that IGWs alone produce large-scale oscillations in solar rotation, and explores how magnetic processes and composition gradients help preserve uniform rotation.

Findings

IGWs induce large-scale rotational oscillations in the Sun.

Magnetic processes like the Tayler-Spruit dynamo can flatten rotation profiles.

Molecular weight gradients inhibit mechanisms, allowing a rapidly rotating core.

Abstract

Internal gravity waves (IGWs) are naturally produced by convection in stellar envelopes, and they could be an important mechanism for transporting angular momentum in the radiative interiors of stars. Prior work has established that they could operate over a short enough time scale to explain the internal solar rotation as a function of depth. We demonstrate that the natural action of IGWs is to produce large scale oscillations in the solar rotation as a function of depth, which is in marked contrast to the nearly uniform rotation in the outer radiative envelope of the Sun. An additional angular momentum transport mechanism is therefore required, and neither molecular nor shear-induced turbulent viscosity is sufficient to smooth out the profile. Magnetic processes, such as the Tayler-Spruit dynamo, could flatten the rotation profile. We therefore conclude that IGWs must operate in conjunction with magnetic angular momentum transport processes if they operate at all. Furthermore, both classes of mechanisms must be inhibited to some degree by mean molecular weight gradients in order to explain the recent evidence for a rapidly rotating embedded core in the Sun.