Reflection and Ducting of Gravity Waves Inside the Sun

TL;DR

This paper investigates how internal gravity waves in the Sun are reflected and ducted by magnetic fields in the tachocline, revealing mechanisms that influence wave energy transmission and potential instabilities.

Contribution

It introduces a simple Cartesian model to demonstrate wave reflection and ducting caused by magnetic fields, highlighting their effects on wave propagation and possible instabilities.

Findings

Magnetic fields can reflect gravity waves, preventing energy from reaching the deep interior.

Wave ducts can form, trapping and amplifying wave modes.

Helical waves may generate an alpha-effect and lead to instabilities.

Abstract

Internal gravity waves excited by overshoot at the bottom of the convection zone can be influenced by rotation and by the strong toroidal magnetic field that is likely to be present in the solar tachocline. Using a simple Cartesian model, we show how waves with a vertical component of propagation can be reflected when traveling through a layer containing a horizontal magnetic field with a strength that varies with depth. This interaction can prevent a portion of the downward-traveling wave energy flux from reaching the deep solar interior. If a highly reflecting magnetized layer is located some distance below the convection zone base, a duct or wave guide can be set up, wherein vertical propagation is restricted by successive reflections at the upper and lower boundaries. The presence of both upward- and downward-traveling disturbances inside the duct leads to the existence of a set of horizontally propagating modes that have significantly enhanced amplitudes. We point out that the helical structure of these waves makes them capable of generating an alpha-effect, and briefly consider the possibility that propagation in a shear of sufficient strength could lead to instability, the result of wave growth due to over-reflection.