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Aeroacoustics of volcanic jets: Acoustic power estimation and jet velocity dependence
Author(s) -
Matoza Robin S.,
Fee David,
Neilsen Tracianne B.,
Gee Kent L.,
Ogden Darcy E.
Publication year - 2013
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2013jb010303
Subject(s) - jet (fluid) , aeroacoustics , acoustics , jet noise , sound power , mach number , physics , noise (video) , volcano , computational aeroacoustics , context (archaeology) , scaling , acoustic emission , geology , mechanics , sound pressure , seismology , sound (geography) , geometry , computer science , mathematics , paleontology , artificial intelligence , image (mathematics)
A fundamental goal of volcano acoustics is to relate observed infrasonic signals to the eruptive processes generating them. A link between acoustic powerΠ ¯ and volcanic gas exit velocity V was proposed by Woulff and McGetchin (1976) based upon the prevailing jet noise theory at the time (acoustic analogy theory). We reexamine this approach in the context of the current understanding of jet noise, using data from a laboratory jet, a full‐scale military jet aircraft, and a full‐scale rocket motor. Accurate estimates ofΠ ¯ require good spatial sampling of jet noise directionality; this is not usually possible in volcano acoustic field experiments. Typical volcano acoustic data better represent point measurements of acoustic intensityI ¯ ( θ ) at a particular angle θ from the jet axis rather thanΠ ¯ . For pure air jet flows, velocity‐scaling laws currently proposed for acoustic intensity differ from those for acoustic power and are of the formI ¯ ( θ ) ∼ ( V / c )n θ, where c is the ambient sound speed and n θ varies nonlinearly from ∼5 to 10 as a function of temperature ratio and angle θ . Volcanic jet flows are more complex than the pure air laboratory case, which suggests that we do not currently know how the exponent n θ varies for a volcanic jet flow. This indicates that the formulation of Woulff and McGetchin (1976) can lead to large errors when inferring eruption parameters from acoustic data and thus requires modification. Quantitative integration of field, numerical, and laboratory studies within a modern aeroacoustics framework will lead to a more accurate relationship between volcanic infrasound and eruption parameters.