Computational Techniques for the Study of Infrasound Propagation in the Atmosphere

Modified ray-mode (phase) theory: Understanding counter-wind propagation effects from atmospheric explosions

“…Despite the fact that ordinary ray theory, does not predict up-wind refractive arrivals from the stratospheric region, the Pierce-Posey wave amplitude, normal mode code consistently predicts the presence of such weak signals at the ''first bounce'' range and with the correct timing for up-wind locations. This full-wave propagation code is a hallmark accomplishment of atmospheric acousticgravity wave theory as originally developed by Pierce (1967) and by Pierce and Kinney (1976). In addition, detailed empirical amplitude analyses have also been constructed from additional low-altitude sources such as meteor fireballs or large bolides (Edwards et al, 2006), which also demonstrate weak signal detections for counter-wind conditions as well as for the more common, down-wind and cross-wind type situations.…”

Development of an Infrasound Propagation Modeling Tool Kit

“…Pierce developed a computer code based on the normal mode theory for infrasound propagation in a relatively low frequency band of interest, motivated by interest in long range propagation of infi-asound due to large (i.e., megaton yield) events [Pierce and Kinney, 1976;Pierce et ah, 1973;Pierce and Posey, 1970]. The normal mode approach is generally usefiil for estimating received time series or waveforms.…”

“…The baseline set of acoustic propagation models contained in InfraMAP consists of: ■ Ray Tracing: a three-dimensional ray theory model, HARPA (Hamiltonian Ray-Tracing Program for Acoustic Waves in the Atmosphere) [Jones et al, 1986], ■ Normal Modes: a WKB version [Dighe et al, 1998;Hunter and Whitaker, 1997] of the normal mode model [Pierce and Kinney, 1976;Pierce et al, 1973;Pierce and Posey, 1970], and ■ PE: a continuous-wave, two-dimensional parabolic equation (PE) model [Jensen et al, 1994;West era/., 1992]. InfraMAP provides integration of these three models with the environmental characterizations described above.…”

On the volcanic waveguide

“…In the case of strong winds, rough topography, and large station distances wher. e atmospheric refraction, diffraction, and ducting may alter the character of the acoustic waves, more sophisticated propagation models must be invoked [Pierce and Kinney, 1975].…”