In Hurlburt et al. (1986, 1994), Cattaneo et al. (1991) or Bogdan et al. (1993), it is the dynamical viscosity $\mu = \rho \nu$ which is constant. However, the kinematic viscosity becomes very large as the density tends to zero leading to a highly viscous surface layer.

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Hereafter, we will simply refer to ${\cal K}$ as the radiative conductivity.

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... $\widehat{\rho w}(\ell,z,t)$

Here and in the following, we define the horizontal wavenumber as $k_x = (2\pi/L_x)\ \ell=(\pi/2)\ \ell$ , where $\ell$ denotes the mode degree and is a non-zero positive integer, $\ell = [1,\ 2, \dots]$ , as purely radial g-modes cannot exist (e.g., Turner 1973).

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