Acoustic Energy Measured From Mesocyclones and Tornadoes in June 2003

The U.S. Army Research Laboratory has developed a low-cost, mobile, rugged, acoustic sensor for surveillance, detection, identification, and location of targets using unattended microphone sensors to measure infrasonic (<10 Hz) energy. However, it 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 Platta, Maryland tornado passed eight miles from the acoustic sensor and a time series showed several peaks in the spectrum. It was decided to investigate the infrasonic spectrum of a variety of storm types and environments during a field exercise in June 2003. The exercise was designed to collect data from severe thunderstorms, supercells, and tornadic storms and study the low-frequency sound generated from these atmospheric phenomena. During the three-week time frame for this exercise, numerous storms were sampled and documented including a small tornado on 9 June near Spearman, Texas, two strong supercells near Olney, Texas, and two supercells in northcentral Nebraska on 21 June. The highlight of these data collections was during the 24 June 2003 outbreak of tornadoes in South Dakota. this paper will discuss the collection methods, documentation of these data, and comparisons of the acoustic energy between the F4 La PLata tornado and the storms sampled in June 2003.