A Preliminary Assessment of Infrasonic Tornado Detection via Comparison with Dual-Polarization Doppler Radar

Prior studies have hypothesized that tornadoes are capable of emitting infrasonic acoustic waves in the infrasound range (<1-20 Hz), however various technological limitations have limited their study and validation. Through a joint effort between the University of Alabama in Huntsville (UAH) and General Atomics - Electromagnetics Systems Group (GA-EMS), a long-term network of mobile and static infrasound detection arrays have been constructed in North Alabama to further investigate infrasonic tornadic emissions. Utilizing the aforementioned infrasound detection arrays in addition to a dense meteorological observation network (including atmospheric profiling systems and radiosondes that will be deployed for potential tornado events to define the structure and evolution of thermodynamic and wind profiles relevant to sound propagation), the primary objectives of this study are to answer the following questions:

• Are infrasound emissions a reliable inficator of tornadoes?
• To what extent does tornado strength does tornado strength have on the presence of infrasonic emissions?
• What correlation do radar radar derived tornado tracks have with those estimated from infrasound?
• To what extent can tornado detection benefit the pre-existing radar network?

 In order to evaluate whether or not tornado emitted infrasound can be used reliably for tornado detection and tracking, advanced signal processing techniques are applied to data collected by the network of infrasound arrays, from which information regarding the bearing and location of the infrasonic source are estimated. The infrasound-determined tornado tracks are then compared to those derived from radar signatures (Doppler velocity couplets, spectrum width maxima, tornadic debris signatures), in addition to ground-truth tracks from damage surveys, to quantify the accuracy of infrasound-based tornado tracking. Results from this comparative analysis will also be used to refine and tune the algorithms used to estimate tornado bearing and location. Further investigation of the data collected will be used to determine how IS tornado detection may supplement or enhance radar detection of tornadoes, particularly in dynamic convective environments in which tornadogenesis may occur rapidly between scan times or in locations with poor low-level radar coverage.

 This presentation showcases preliminary results from the first long-term, geographically dense infrasound observation network aimed at tornado detection. Using comprehensive analyses, we present a first look at how these observations compare with those derived from radar. Initial findings regarding the operational utility of infrasonic tornado signals will be discussed, along with addressing the possible limitations and future research regarding infrasonic tornado detection.