|Title||Aeroacoustics of volcanic jets: Acoustic power estimation and jet velocity dependence|
|Publication Type||Journal Article|
|Year of Publication||2013|
|Authors||Matoza RS, Fee D, Neilsen T.B, Gee K.L, Ogden D.E|
|Journal||Journal of Geophysical Research-Solid Earth|
|Type of Article||Article|
|Keywords||acoustic intensity; acoustic power; computational aeroacoustics; explosions; gas exit; generation; infrasound; noise; prediction; propagation; scaling laws; sound; source parameters; turbulence; velocity; volcano infrasound|
A fundamental goal of volcano acoustics is to relate observed infrasonic signals to the eruptive processes generating them. A link between acoustic power 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 of 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 intensity at a particular angle from the jet axis rather than . For pure air jet flows, velocity-scaling laws currently proposed for acoustic intensity differ from those for acoustic power and are of the form I approximate to n, where c is the ambient sound speed and n varies nonlinearly from approximate to 5 to 10 as a function of temperature ratio and angle . Volcanic jet flows are more complex than the pure air laboratory case, which suggests that we do not currently know how the exponent n 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.