Acoustic Energy Measured in Severe Storms during a Field Study in June 2003

Abstract : The U.S. Army Research Laboratory (ARL) has developed a low-cost, mobile, rugged, non-line-of-sight acoustic sensor for surveillance, detection, identification, and locations of targets using unattended microphone sensors to measure infrasonic (<10 Hz) energy. However, it also was discovered that the acoustic sensor is capable of measuring background noise sources such as thunderstorms and severe weather. On 28 April 2002, the F4 La Plata, Maryland, tornado passed 13 km from the acoustic sensor and a time series showed a series of peaks in the spectrum. ARL decided to investigate the infrasonic spectrum in a variety of storm environments in a field study in June 2003. During the 3-week study, several severe storms, mesocyclones, and tornadoes were sampled in the Central Plains of the United States. These storms included a small tornado on 9 June 2003 near Spearman, TX; two strong mesocyclones near Olney, TX; and two supercells in north central Nebraska on 21 June 2003. The highlight of the data collection was during the 24 June 2003 outbreak of tornadoes in South Dakota. This report discusses the data collection, documentation, and structure of these storms. Based on the observations and data collected there is apparently a correlation between tornadic storms and storms that record less than 10 Hz signals in this study.