Correlation of Winds and Geographic Features with Production of Certain Infrasonic Signals in the Atmosphere

Abstract

Of the waves which propagate in the atmosphere at acoustic velocity in the period range from 10 to 100 s, one type has been classified by triangulation as arising principally from mountainous regions. These signals were first described as ' northwesters ' or ' 310 ers ' by the NBS Geoacoustics Group under R. K. Cook at Washington, D.C., from the predominant direction of arrival. Subsequent operation of an observatory at Boulder, Colorado by Vernon Goerke gave a source region by triangulation in the Pacific Northwest, primarily in Montana and Alberta. Installations of observatories at College, Alaska (Wilson) and Pullman, Washington-Moscow, Idaho (Craine and Thomas) enlarged the data base available, and triangulation showed the principal source areas to be along the coast of British Columbia and in the inland Rocky Mountains of the British Columbia-Alberta border. This paper discusses the presently known characteristics of this class of infrasonic waves, locates the triangulation areas, reviews selected events, and suggests that certain of these waves are produced as aerodynamic sound. The paper shows a correlation between the 500 mb jet stream velocity and direction in these mountainous regions, and the detection of these atmospheric pressure waves. Infrasonic waves-10to 100-s periodsThere are a number of atmospheric wave structures travelling at acoustic velocities that appear in the 10-to 100-s period range. An observatory, through four pressure sensitive transducers, provides basic information on the amplitude variations of pressure with time, from which the waveform, period, and time sequence of the event at an individual microphone can be obtained. By overlaying the charts and visually correlating the waveforms from several transducers, a signal can be identified in the noise, and arrival time differences measured. The azimuth of the direction of arrival, and the horizontal velocity across the transducer array, can then be calculated, assuming a plane wave. Detection of signals is often difficult, since local wind noise may obscure the desired signal, and changes in waveform caused by frequency dispersion of the signal or the effects of other signals arriving from different directions may make the waveform vary at each transducer. We define an ' event ' as a series of signals that appear to be related. 201 0 pr) FIG. 2. Correlation of mountain-associated waves at Pullman, Washington, at 1430 UT on 1968 November 28. Mean azimuth 329O, trace velocity 426 m s-l; approximate peak-to-peak amplitude 6 3 dyn cm-*; average period 50 s. facing page 202 Correlation of winds and geographic features 5 -203 15 10

Infrasound and Gravity Waves Over the Andes Observed by a Pressure Sensor on Board a Stratospheric Balloon

“…Mountain‐generated infrasound is still a poorly understood phenomenon; very few theoretical and experimental works treat this subject (Bedard, ; Chimonas, ; Chunchuzov, ; Hupe, ; Larson et al, ). According to these works, the mountains infrasound are probably generated by the wind blowing into the mountain valleys or to turbulence at mountain ridges.…”

Martian Infrasound: Numerical Modeling and Analysis of InSight's Data

“…Particularly on Mars, it may allow the remote investigation of meteor entries (Williams, 2001) and related impacts (Daubar et al, 2018), as well as possible nearby landslides, rockfalls, or ejecta falls. Based on terrestrial analogues, one can also reasonably expect acoustic signals from spacecraft entry (Garcés et al, 2004;Yamamoto et al, 2011), the seismo-acoustic coupling of marsquakes (Krishnamoorthy et al, 2018(Krishnamoorthy et al, , 2019Martire et al, 2018), dust devils (Bedard, 2005;Lorenz & Christie, 2015;Tatom et al, 1995), wind-mountain interactions (Larson et al, 1971), and atmospheric turbulence (Howe, 2002).…”

Systematic Array Processing of a Decade of Global IMS Infrasound Data

“…Hotspots of sources, inferred to be MAW, are found in local winter over the Himalayas, the Rocky and Andes Mountains in America (Le Pichon et al 2010). Some activity is found over New Zealand where the chain of the Southern Alps culminates at 3700 m. Earlier work published by Larson et al (1971) pointed out similar features for MAW traveling at acoustic velocities in the 10-100 s period range. Statistical analyses of long-duration atmospheric waves, lasting for several hours to several days were carried out.…”