Development of high altitude balloon based sensing of low frequency sounds from severe storms*

There is evidence that tornadoes emit sound at frequencies below human hearing, which is called infrasound. This has been detected from ground-based sensors, but the ability to detect at the ground is very sensitive to atmospheric conditions. Our team has helped pioneer the ability to record infrasound from high altitude balloons called heliotropes. Heliotropes are free-floating solar balloons that float within the lower stratosphere (~20 km) throughout the daytime. Use of balloons significantly mitigates the wind noise problem that is common for most infrasound measurements, but some relative motion will exist as the sensors are dragged below the balloon envelope. This talk will present details on the development of a mounting system to mitigate wind noise. In addition, details of heliotrope operations and flight performance will be discussed, including the planning required to intercept a severe storm.