Internal gravity wave excitation by turbulent convection
Abstract
We calculate the flux of internal gravity waves (IGWs) generated by turbulent convection in stars. We solve for the IGW eigenfunctions analytically near the radiativeconvective interface in a local, Boussinesq and Cartesian domain. We consider both discontinuous and smooth transitions between the radiative and convective regions and derive Green's functions to solve for the IGWs in the radiative region. We find that if the radiativeconvective transition is smooth, the IGW flux depends on the exact form of the buoyancy frequency near the interface. IGW excitation is most efficient for very smooth interfaces, which gives an upper bound on the IGW flux of ∼F_{conv}(d/H), where F_{conv} is the flux carried by the convective motions, d is the width of the transition region and H is the pressure scale height. This can be much larger than the standard result in the literature for a discontinuous radiativeconvective transition, which gives a wave flux {∼ } F_conv {M}, where {M} is the convective Mach number. However, in the smooth transition case, the most efficiently excited perturbations will break in the radiative zone. The flux of IGWs which do not break and are able to propagate in the radiative region is at most {∼ } F_conv {M}^{5/8} (d/H)^{3/8}, larger than the discontinuous transition result by ({M}H/d)^{3/8}. The transition region in the Sun is smooth for the energybearing waves; as a result, we predict that the IGW flux is a few to five times larger than previous estimates. We discuss the implications of our results for several astrophysical applications, including IGWdriven mass loss and the detectability of convectively excited IGWs in mainsequence stars.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 April 2013
 DOI:
 10.1093/mnras/stt055
 arXiv:
 arXiv:1210.4547
 Bibcode:
 2013MNRAS.430.2363L
 Keywords:

 convection;
 hydrodynamics;
 waves;
 Sun: oscillations;
 Astrophysics  Solar and Stellar Astrophysics;
 Physics  Fluid Dynamics
 EPrint:
 14 pages, 3 figures, accepted to MNRAS