What is it about?
The common approach to calculate infrasound propagation in the atmosphere consists in solving the acoustic equation in a given background atmospheric state. This approach captures the most significant ducts, but sometimes it fails in predicting important wavepackets that are related to small-scale atmospheric fluctuations. As in the troposphere these fluctuations are mainly produced by mountains, the contribution of these mountains to infrasound propagation remains an important open question.
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Why is it important?
The central result of this paper is that mountain wave dynamics may lead to strong attenuation or amplification of upcoming acoustic waves, regarding to the direct "mask" effect the mountain has on acoustic propagation. For a stable flow the mountain wave dynamics produces large horizontal winds and buoyancy disturbances at low level that result in intense downslope winds and Foehn. When the downslope wind is less intense, the flows can reinforce the acoustic waveguide over the mountain and lead to a signal of greater amplitude compared to that obtained by the "mask" effect. The acoustic waveguide is then strongly impacted which leads to a new kind of acoustic absorption.
Perspectives
The present work is related to the more general issue of incorporating unresolved gravity waves variability in infrasound propagation calculations. Recent works suggest that the mismatch between simulated and observed signals is related to the fact that the atmospheric specifications used in most studies do not adequately represent internal gravity waves. In the Atmospheric General Circulation Models which are used to produce the atmospheric specifications, these gravity waves are represented by parameterizations and in return, these parameterizations can be used to predict the gravity waves field used in infrasound studies.
Christophe Millet
CEA
Read the Original
This page is a summary of: An investigation of infrasound propagation over mountain ranges, The Journal of the Acoustical Society of America, January 2018, Acoustical Society of America (ASA),
DOI: 10.1121/1.5020783.
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