Low-Frequency Atmospheric Acoustic Energy Associated with Vortices Produced by Thunderstorms

Abstract

An infrasonic observatory collocated with the Colorado State University CHILL radar during the summer of 1995 permitted unique comparisons between severe storm kinematics and detected acoustic energy at subaudible frequencies near 1 Hz. Radar observations of a velocity couplet aloft (evolving into a tornado) showed a circulation maximum descending for about 30 min while moving to the east. The detected infrasound followed the trend of these observations. A model of sound radiated from vortex systems predicts frequencies in the range observed. These data are interpreted in the context of past infrasonic observations. An ongoing study comparing regional tornado and funnel sightings with archived infrasonic data has identified over 100 cases to date where the infrasonic signals occurred at the time of, and from the direction of, the vortices. For some of these cases, the distances were greater than 100 km. The author and his associates continue to collect datasets to permit further evaluation of infrasonic detection methods.

Conditions That Inhibit the Spontaneous Radiation of Spiral Inertia–Gravity Waves from an Intense Mesoscale Cyclone

“…In addition, due to large values of , typical oscillations of tornadoes and dust devils should not produce IG wave radiation. We must note, however, that tornadoes can have Mach numbers as large as one-half and emit detectable levels of analogous acoustic radiation (e.g., Abdullah 1966;Bedard 2005).…”

Infrasound generation by tornadic supercell storms

“…The acoustic power radiated by a convective storm system could be as high as 10 7 watts (Georges, 1988). Although several reasonable mechanisms have been suggested to explain this acoustic radiation, the physical mechanism of the process still remains unexplained (Colgate and McKee, 1969;Georges and Greene, 1975;Beasley et al, 1976;Georges, 1988;Bedard and Georges, 2000;Bedard, 2005). It has to be noted that, in addition to acoustic radiation, severe weather systems also generate much lower-frequency Lamb waves (Pielke et al, 1993;Pielke, 1994a,b, 2000).…”

Electrical Role for Severe Storm Tornadogenesis (and Modification)

“…Low frequency (1 Hz) infrasonic observations coordinated with Doppler radar measurements were reported by Bedard [33] in which a vortex whose maximum circulation was detected within an IC storm on 7 June 1995 in eastern Colorado and then was tracked on an eastwardly descending direction for approximately 30 minutes before evolving into a full-fledged tornado on the ground. The infrasonic method, that had been included in the mentioned survey by Neubert et al [31] of electrical discharges in the mesosphere, provides for detection at distances up to ~1000 km, as also described by Bedard, and relates to monitoring of the acoustic energy contained in radial modes of vortex vibrations.…”