On adiabatic oscillations of a stratified atmosphere on the flat earth

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We consider the oscillations of the atmosphere around a stratified back ground density and entropy distribution under the gravitation on the flat Earth. The atmosphere is supposed to be an ideal gas, and the motion is supposed to be governed by the compressible Euler equations. The density distribution of the background equilibrium is supposed to touch the vacuum at the finite height of the stratosphere. Considering the linearized approximation for small perturbations, we show that time periodic oscillations with a sequence of time periods, which accumulate to infinity, say, slow and slow oscillations, so called “g-modes,” can appear when the square of the Brunt–Väisälä frequency is positive everywhere for the considered background equilibrium.