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Published September 21, 2015 | Submitted + Published
Journal Article Open

The properties of g-modes in layered semiconvection


We study low-frequency waves that propagate in a region of layered semiconvection. Layered semiconvection is predicted to be present in stellar and planetary interiors and can significantly modify the rate of thermal and compositional mixing. We derive a series of analytical dispersion relations for plane-parallel layered semiconvection in the Boussinesq approximation using a matrix transfer formalism. We find that like a continuously stratified medium, a semiconvective staircase – in which small convective regions are separated by sharp density jumps – supports internal gravity waves (g-modes). When the wavelength is much longer than the distance between semiconvective steps, these behave nearly like g-modes in a continuously stratified medium. However, the g-mode period spacing in a semiconvective region is systematically smaller than in a continuously stratified medium, and it decreases with decreasing mode frequency. When the g-mode wavelength becomes comparable to the distance between semiconvective steps, the g-mode frequencies deviate significantly from those of a continuously stratified medium (the frequencies are higher). g-modes with vertical wavelengths smaller than the distance between semiconvective steps are evanescent and do not propagate in the staircase. Thus, there is a lower cut-off frequency for a given horizontal wavenumber. We generalize our results to gravitoinertial waves relevant for rapidly rotating stars and planets. Finally, we assess the prospects for detecting layered semiconvection using astero/planetary seismology.

Additional Information

© 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 June 26. Received 2015 June 26. In original form 2015 May 20. First published online July 25, 2015. We thank Pascale Garaud for fruitful discussions on stellar and planetary oscillations and semiconvection. This work was supported in part by the Theoretical Astrophysics Center at UCB, by a Simons Investigator award from the Simons Foundation to EQ, and by the David and Lucile Packard Foundation. JF acknowledges partial support from NSF under grant no. AST-1205732 and through a Lee DuBridge Fellowship at Caltech.

Attached Files

Published - MNRAS-2015-Belyaev-2700-11.pdf

Submitted - 1505.05492v2.pdf


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