Dissipation of acoustic–gravity waves in the Earth’s thermosphere

The dissipation of acoustic–gravity waves in the thermosphere due to molecular viscosity and thermal conductivity based on a modified system of hydrodynamic equations is studied. A modification of the system of equations consists in additional taking into account in the linearized Navier–Stokes equations and heat transfer additional terms describing the transfer of momentum and energy due to the background density gradient, except for the usually taken into account velocity gradient. Using these modified equations, the local dispersion equation of acoustic–gravity waves in an isothermal dissipative atmosphere is obtained. On this basis, new general expressions for the attenuation rates in time and in space for both acoustic and gravity waves in the entire spectral range are derived in the paper. The relationship between the rates of AGW temporal and spatial attenuation is analyzed. The results obtained are consistent with satellite-based observations of AGW at the heights of the thermosphere, indicating filtering of the wave spectrum due to viscosity and thermal conductivity.