Infrasound Originating Near Mountainous Regions in Colorado

Abstract

An array of infrasonic microphones, installed near Fraser, CO, operated from February through June 1973. This observatory, in conjunction with a similar, permanent installation at Boulder, triangulated on sources of infrasound in Colorado. We found that the lee of a group of mountains that includes Long's Peak is a preferred source region for infrasound. Heretofore, such triangulations used long propagation paths usually of hundreds of kilometers, which resulted both in poorly defined source regions and signal source characteristics. The generation of local infrasound is probable when the 500 mb winds are high. A comparison with Boulder's historical data shows that most signals occur during the winter months with durations longer than 3 h. One case study presented shows that source motion can occur (20 km over an 8 h period). The identification of a local, accessible infrasonic source region offers wide opportunities for further research (e.g., the study of an active source region using time-lapse photography, dual-Doppler radar, lidar and instrumented aircraft). Comparisons of infrasonic data with measurements of turbulence reported by aircraft suggest a temporal and spatial relation between sources of infrasound and aircraft turbulence encounters.