Characterization of absorption and non-linear effects in infrasound propagation using an augmented Burgers’ equation

Abstract

The long-range atmospheric propagation of explosion-like waves of frequency in the infrasound range is investigated using non-linear ray theory. Simulations are performed for sources of increasing amplitude on rays up to the lower thermosphere and for distances of hundreds of kilometres. A study of the attenuation of the waveforms observed at ground level induced by both the classical mechanisms and the vibrational relaxation of the molecules comprising the atmospheric gas is carried out. The relative importance of classical absorption and vibrational relaxation along the typical atmospheric propagation trajectories is assessed. Non-linear effects are highlighted as well and particular emphasis is placed on their strong interaction with absorption phenomena. A detailed description of the propagation model and of the numerical algorithm used in this work is first reported. Results are then discussed and the importance of the different mechanisms is clarified.

Modeling of Ionospheric Responses to Atmospheric Acoustic and Gravity Waves Driven by the 2015 Nepal 7.8 Gorkha Earthquake

“…MAGIC solves compressible, nonlinear Navier‐Stokes equations as described in Snively () and Zettergren and Snively (), based on shock‐capturing finite volume methods of Langseth and LeVeque () and Bale et al () in a modified version of Clawpack 4.2 (Clawpack Development Team, ; LeVeque, ). MAGIC accounts for nonlinearity and dissipation effects which play a crucial role on the propagation of AGWs (e.g., Heale et al, ; Sabatini et al, , ). In particular, the need to accurately resolve the nonlinear effects of AWs at the near‐epicentral region, where the amplitudes of vertical fluid velocities of AWs reach 300 m/s, is one of the main challenges in the current study.…”

Three-dimensional direct numerical simulation of infrasound propagation in the Earth’s atmosphere

“…Another underlying assumption of the present model is the negligibility of relaxation effects, but, as shown by Sabatini et al (2016b), non-equilibrium phenomena mainly affect tropospheric and stratospheric waves of frequency greater than 1 Hz.…”

“…The atmospheric stratification imposed by the gravity force has a considerable impact on acoustic propagation. The roughly exponential reduction with altitude of the mean atmospheric density indeed tends to amplify nonlinearities, which leads to signal steepening and lengthening (Rogers & Gardner 1980;Lonzaga et al 2015;Sabatini et al 2016b). Likewise, thermoviscous absorption augments as the mean atmospheric density diminishes, due to the increase of the mean kinematic viscosity (Sutherland & Bass 2004).…”

“…Likewise, thermoviscous absorption augments as the mean atmospheric density diminishes, due to the increase of the mean kinematic viscosity (Sutherland & Bass 2004). Relaxation phenomena may also damp infrasonic waves, in particular those propagating in the troposphere and in the stratosphere (Sabatini et al 2016b). Moreover, acoustic energy can be scattered by fine-scale temperature and wind inhomogeneities generated by internal gravity waves (Kulichkov 2004;Chunchuzov et al 2011;Chunchuzov, Kulichkov & Firstov 2013;Chunchuzov et al 2014Chunchuzov et al , 2015.…”

“…Given the complexity of the physics to be taken into account, numerical simulations of atmospheric propagation have necessarily been based on simplified approaches. Ray tracing (Rogers & Gardner 1980;Lonzaga et al 2015;Sabatini et al 2016b;Scott, Blanc-Benon & Gainville 2017), normal modes (Waxler 2002(Waxler , 2004Bertin, Millet & Bouche 2014; and oneway models (Lingevitch, Collins & Siegmann 1999;Ostashev et al 2001;Le Pichon, Ceranna & Vergoz 2012;Gallin et al 2014) have been the most commonly used techniques. Albeit computationally efficient, they are not able to account for all the aforementioned physical phenomena.…”