Evanescent acoustic-gravity modes in the isothermal atmosphere: systematization, applications to the earth's and solar atmospheres

Abstract

Abstract. The objects of research in this work are evanescent wave modes in a gravitationally stratified atmosphere and their associated pseudo-modes. Whereas the former, according to the dispersion relation, rapidly decrease with distance from a certain surface, the latter, having the same dispersion law, differ from the first by the form of polarization and the character of its decreasing away from the surface. Within a linear hydrodynamic model, the propagation features of evanescent wave modes in an isothermal atmosphere are studied. Research carried out for different assumptions about the properties of the medium. On this way, a new wave mode – anelastic evanescent wave mode – was discovered. Also, the possibility of the existence of a pseudo-mode related to it is indicated. The case of two isothermal media differing in temperature at the interface is studied in detail. It is shown that a non-divergent pseudo-mode with the dispersion of solar f-mode type can be realized on the interface for the specified horizontal scale. The newly discovered dispersion relation, at the interface of two media, is satisfied by the wave mode, which has different types of amplitude versus height dependencies at different horizontal scales. The applicability of the obtained results to clarify the properties of f-mode observed on the Sun is analyzed.

Attenuation of Evanescent Acoustic-Gravitational Modes in the Earth’s Thermosphere

“…The solutions for the amplitudes of the perturbed values of the f-mode in the atmosphere with dissipation have the form: (15) The polarization relations for the velocity components of the f-mode coincide with the case of an isothermal atmosphere without dissipation [8].…”

“…For the f-mode, we put in equations ( 2)-( 5) [8,16,21]. Taking this condition into account, we obtain the following from ( 5):…”

“…For the inelastic γ-mode in system ( 2)-( 5), we put (see [8]), whence we obtain the following relation between the velocity components: (16) Then, taking into account (16), it follows from equation ( 2) that . To solve ( 6) from ( 3)-( 5), we get:…”

“…However, under certain conditions, evanescent horizontal wave modes can also exist in the atmospheres of planets and on the Sun [7,21]. To date, the role of evanescent waves in the dynamics and energetics of atmospheric processes has been studied much less [8,9,16,21].…”

“…To do this, we will use a modified system of Navier-Stokes equations and thermal conductivity. Of particular interest is the attenuation of the γ-mode, the possibility of which was recently theoretically shown in [8]. Now the possibility of its experimental observations is being studied, taking into account the realistic features of the atmosphere.…”