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 nature of decrease from the surface. Within a linear hydrodynamic model, the propagation features of evanescent wave modes in an isothermal atmosphere are studied. Research is carried out for different assumptions about the properties of the disturbances. In this way, a new wave mode – anelastic evanescent wave mode – was discovered that satisfies the dispersion relation ω2=kxgγ-1. 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 a horizontal scale kx∼1/2H1 can be realized on the interface with dispersion ω2=kxg. Dispersion relation ω2=kxgγ-1 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 kx. The applicability of the obtained results to clarify the properties of the f-mode observed on the Sun is analyzed.
Highlights
Acoustic-gravity waves (AGWs) in the Earth’s atmosphere have been studied theoretically and experimentally for more than 60 years
ND and Anelastic mode (AE) are indistinguishable at the points of intersection with Lamb pseudomodes (Lp) and BV pseudo-modes (BVp)
With the f -mode observed on the Sun, one should identify the mode that we classify as the ND mode, for which www.ann-geophys.net/37/405/2019/
Summary
Acoustic-gravity waves (AGWs) in the Earth’s atmosphere have been studied theoretically and experimentally for more than 60 years. Cheremnykh et al.: Evanescent acoustic-gravity modes in the isothermal atmosphere dicate waveguide or evanescent (along a horizontal surface) propagation of at least part of the observed waves. As well as freely propagating AGWs, evanescent wave modes play an important role in atmospheric dynamics of the Sun and planets. Evanescent waves propagate horizontally in an atmosphere, vertically stratified by gravity, subject to the presence of vertical gradients of parameters. The energy of these waves should decrease both up and down from the level at which they are generated. In the Earth’s atmosphere, such waves can be efficiently generated at sharp vertical temperature gradients, for example, at the base of the thermosphere or at the heights of the tropopause and mesopause. The possibility of realizing the evanescent modes in the model of a thin temperature gap is studied
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