Numerical Modeling of the Propagation of Infrasonic Acoustic Waves Through the Turbulent Field Generated by the Breaking of Mountain Gravity Waves

Abstract

The nonlinear propagation of low‐frequency acoustic waves through the turbulent fluctuations induced by breaking mountain gravity waves is investigated via 2‐D numerical simulations of the Navier‐Stokes equations, to understand the effects of atmospheric dynamics on ground‐based infrasound measurements. Emphasis is placed on acoustic signals of frequency around 0.1 Hz, traveling through tens‐of‐kilometers‐scale gravity waves and subkilometer‐scale turbulence. The sensitivity of the infrasonic phases to small‐scale fluctuations is found to depend on the altitudes through which they are refracted toward the Earth. For the considered cases, the dynamics in the stratosphere impact the refracting acoustic waves to a greater extent than those in the thermosphere. This work clearly demonstrates the need for accurate descriptions of the effects of atmospheric dynamics on acoustic propagation, such as here captured by the full set of fluid dynamic equations, as well as of the subsequent effects on measured signals.

Inferring the Evolution of a Large Earthquake From Its Acoustic Impacts on the Ionosphere

“…However, the durations, amplitudes, and times of arrival of the resulting N-waves at far distances do depend on the source characteristics (Howes, 1967;T.-P. Liu, 1977). In general, however, the shape of N-waves may be distorted by atmospheric stratification, winds, and turbulence (Crow, 1969;Marchiano et al, 2005;Pierce & Maglieri, 1972;Sabatini, Snively, et al, 2019), as well as nonlinear effects and wave focusing (Inoue & Yano, 1997;Sabatini, Marsden, et al, 2019). Also, for earthquakes, the dynamics are complicated by the initial formation of acoustic shocks that may evolve at different altitudes due to the spatial and temporal variability of IAW sources.…”

Identification of Acoustic Wave Signatures in the Ionosphere From Conventional Surface Explosions Using MF/HF Doppler Sounding

“…In addition to the high frequency attenuation effect of the atmosphere, there are nonlinear effects that generate spectral content as well. Higher frequencies are generated through steepening wavefronts, and lower frequencies are generated through the fact that the positive phase of pressure wave travels faster than the negative phase (Hamilton & Blackstock, 2008; Inchin et al., 2021; Lonzaga et al., 2015; Sabatini et al., 2019). A combination of attenuation and nonlinear evolution impart noticeable changes the spectral content.…”

“…Furthermore, the presence of turbulence and other atmospheric waves produce a complicated medium for infrasound propagation. These effects, along with a varying wind profile can severely modify the arrival time of infrasound at a given altitude (P. Blom, 2019; Evers & Haak, 2009; Sabatini et al., 2019).…”

SPECFEM2D-DG, an open-source software modelling mechanical waves in coupled solid–fluid systems: the linearized Navier–Stokes approach

“…The ability to load range-dependent atmospheric models can be used to model acoustic propagation perturbed by other physical phenomena, provided their temporal variations are slow compared to the overlaying acoustic waves, for instance gravity waves (Sabatini et al 2019).…”