Infrasonic waves generated in the lower atmosphere can propagate into the thermosphere and perturb the ionosphere. These disturbances are accompanied by a change in the ionospheric electron density, which can be detected via remote sensing methods, such as Global Navigation Satellite System derived measurements of integrated total electron content. The altitude-dependent decrease in density strengthens dissipative phenomena which affect these measurements by reducing the acoustic-wave amplitude. Sutherland and Bass [https://doi.org/10.1121/1.1631937] have described atmospheric absorption, but only up to 160 km, and neglected interspecies diffusion. However, the atmosphere above the mesopause is a mixture of three major gases, namely, N2, O2, and O, where processes associated with mass-fraction-density gradients could affect acoustic-energy dissipation. This work revisits absorption processes via numerical simulations of the equations of fluid mechanics for multicomponent-gas mixtures, under the assumption of a small Knudsen number (i.e., satisfying continuum approximation). More specifically, diffusion due to mole-fraction, pressure, and temperature gradients, and heat diffusion due to concentration gradients are included alongside classical thermo-viscous terms. Their impact is investigated on vertically-propagating acoustic pulses with varying frequencies, <1 Hz, and different amplitudes that match typical values observed from geophysical and anthropogenic sources (e.g., earthquakes, thunderstorms, explosions).

Explosive events, such as artificial or accidental explosions, and volcanic eruptions, among others, generate low-frequency acoustic waves that propagate through and perturb atmospheric and ionospheric layers (e.g., the hydroxyl and oxygen airglow layers, the sodium layer, and the ionospheric D-region). The subsequent disturbances (i.e., airglow emission intensity, sodium or other minor species density, or electron density fluctuations) are potentially detectable by optical or radio remote sensing methods. Understanding and quantifying the impact of acoustic waves on atmospheric layers are, therefore, crucial steps for establishing detectability thresholds (e.g., relative to source scales and effective yields). In this work, we investigate the propagation of upwardly-traveling acoustic perturbations induced by 1t to-1 kt of TNT-equivalent ground explosions and their signatures on different atmospheric layers. Specifically, we estimate the amplitudes and periods of the induced fluctuations of hydroxyl, sodium, and electron densities at mesospheric through lower-thermospheric altitudes. This work investigates the potential of such layers to serve as sensors for characterizing lower-atmospheric explosive events and the complementarity of such indirect measurements with direct sensing, e.g., of pressure fluctuations in situ.

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