AGW spectrum filtering in a horizontally inhomogeneous atmospheric flow

Heading: 
Space Physics
1Fedorenko, AK, Kryuchkov, EI, 1Cheremnykh, OK, 1Zhuk, IT
1Space Research Institute under NAS and National Space Agency of Ukraine, Kyiv, Ukraine
Kinemat. fiz. nebesnyh tel (Online) 2023, 39(4):55-67
https://doi.org/10.15407/kfnt2023.04.055
Language: Ukrainian
Abstract: 

The properties of acoustic-gravity waves in the atmosphere can be determined to a greater extent by the characteristics of the propagation medium than by the sources of these disturbances. In the presence of spatial inhomogeneity of atmospheric parameters, significant deviations of the characteristics of AGW from theory are observed. This makes it difficult to experimentally diagnose the waves and find a connection with their potential sources. The analysis of AGW observations on the Dynamics Explorer 2 satellite indicates the predominance of waves with certain spectral characteristics in the polar thermosphere. It was established that the acoustic-gravity waves of large amplitudes are spatially consistent with the regions of strong winds, while AGWs move mainly against the wind. In order to explain the observed properties of AGW, the filtering of the spectrum of these waves in the presence of spatially inhomogeneous wind was investigated in the paper. It is shown that the direction and magnitude of the wave vector change in a special way in the oncoming inhomogeneous wind. At the same time, as the speed of the oncoming wind increases, the wave vector gradually inclines to the horizontal plane. The vertical component of the wave vector rapidly decreases, and its horizontal component tends to some limiting value, which is predominant in observations. In addition, an increase occurs in the frequencies and amplitudes of waves in the oncoming inhomogeneous flow. As a result, high-frequency wave harmonics with a small angle of inclination of the wave vector to the horizontal plane and a characteristic horizontal wavelength will prevail in a strong headwind from a continuous spectrum of atmospheric AGWs that can be generated by a hypothetical source. Since the wave vector and the group velocity vector in the AGW are almost perpendicular to each other, such waves ensure efficient energy transfer in the vertical direction. In this regard, AGWs play an important role in the energy balance of the polar atmosphere, redistributing the energy of horizontal wind currents in the vertical direction.
Keywords: acoustic-gravity wave, non-homogeneous flow of the atmosphere, spectrum filtering

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