Dissipation
Damping of the tides occurs primarily in the lower thermosphere region, and may be caused by turbulence from breaking gravity waves. A similar phenomena to ocean waves breaking on a beach, the energy dissipates into the background atmosphere. Molecular diffusion also becomes increasingly important at higher levels in the lower thermosphere as the mean free path increases in the rarefied atmosphere.
At thermospheric heights, attenuation of atmospheric waves, mainly due to collisions between the neutral gas and the ionospheric plasma, becomes significant so that at above about 150 km altitude, all wave modes gradually become external waves, and the Hough functions degenerate to spherical functions; e.g., mode (1, -2) develops to the spherical function P11(θ), mode (2, 2) becomes P22(θ), with θ the co-latitude, etc. . Within the thermosphere, mode (1, -2) is the predominant mode reaching diurnal temperature amplitudes at the exosphere of at least 140 K and horizontal winds of the order of 100 m/s and more increasing with geomagnetic activity. It is responsible for the electric Sq currents within the ionospheric dynamo region between about 100 and 200 km altitude.
Read more about this topic: Atmospheric Tide
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