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 sum- mer,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.