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Infrasound propagation in tropospheric ducts and acoustic shadow zones

TitleInfrasound propagation in tropospheric ducts and acoustic shadow zones
Publication TypeJournal Article
Year of Publication2017
Authorsde Groot-Hedlin C.D
JournalJournal of the Acoustical Society of America
Date Published2017/10
Type of ArticleArticle
ISBN Number0001-4966
Accession NumberWOS:000413528900022
Keywordsabsorbing atmosphere; absorption; finite-amplitude; gravity-waves; inhomogeneous moving-media; long-range propagation; parabolic equation; simulation; sound; wave-propagation; wide-angle

Numerical computations of the Navier-Stokes equations governing acoustic propagation are performed to investigate infrasound propagation in the troposphere and into acoustic shadow zones. An existing nonlinear finite-difference, time-domain (FDTD) solver that constrains input sound speed models to be axisymmetric is expanded to allow for advection and rigid, stair-step topography. The FDTD solver permits realistic computations along a given azimuth. It is applied to several environmental models to examine the effects of nonlinearity, topography, advection, and two-dimensional (2D) variations in wind and sound speeds on the penetration of infrasound into shadow zones. Synthesized waveforms are compared to a recording of a rocket motor fuel elimination event at the Utah Test and Training Range. Results show good agreement in the amplitude, duration, and spectra of synthesized and recorded waveforms for propagation through 2D atmospheric models whether or not topography, advection, or nonlinearity is explicitly included. However, infrasound propagation through a one-dimensional, range-averaged, atmospheric model yields waveforms with lower amplitudes and frequencies, suggesting that small-scale atmospheric variability causes significant scatter within the troposphere, leading to enhanced infrasound penetration into shadow zones. Thus, unresolved fine-scale atmospheric dynamics are not required to explain infrasound propagation into shadow zones. (C) 2017 Acoustical Society of America.

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