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L. Tao (Astronomy Department, Columbia University), O.M. Umurhan (Center for Turbulence Research, Stanford University)
Recently Spiegel & Tao studied the linear stability of photoacoustic modes of a plane-parallel atmosphere supported by radiative forces at a moderate fraction of the Eddington luminosity. Their numerical boundary value work showed that the compressional modes are most unstable for horizontal wave numbers of order unity. To gain physical understanding, we generate asymptotic solutions to demonstrate the qualitative similarities between this small wave number photoacoustic instability and Rayleigh's thermoacoustic instability. We discuss the difference between this instability and the photon bubble process discovered recently by Arons and coworkers. Based on preliminary nonlinear simulations, we conclude by suggesting another route to the formation of coherent structures in radiation dominated atmospheres.
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