Frequency-dependent infrasound absorption in the thermosphere and conservative energy-deposition limits

Abstract We present a simplified theoretical model to examine the frequency-dependent attenuation of infrasound propagating vertically through Earth’s upper atmosphere. Focusing exclusively on classical absorption mechanisms, viscosity, and thermal conductivity, the model provides an analytically transparent framework to assess how wave frequency and acoustic pressure affect energy dissipation and associated atmospheric heating. The model enables systematic estimation of the altitude-dependent energy flux and propagation limits for monochromatic plane waves. The results reveal that lower-frequency waves can reach greater altitudes with reduced attenuation, whereas higher-frequency waves dissipate already at lower altitudes. Under certain acoustic conditions, the rate of thermospheric heating due to viscous dissipation may reach or surpass levels comparable to that of solar EUV radiation. While this model deliberately omits nonlinear and spectral complexities, its strength lies in distilling the essential scaling relationships governing acoustic energy transport and heating. These findings offer a foundational reference for more complex models and contribute to the understanding of thermospheric dynamics and ionospheric disturbances. Graphical Abstract