Abstract
Sound at frequencies below the nominal bound of human hearing
(~20 Hz) is called “infrasound.” Infrasound at
frequencies between 0.5 and 10 Hz has been observed to be emitted by
tornado-producing storms throughout the life of the tornado, including
tornadogenesis. Due in part to the low atmospheric attenuation at these
low frequencies, infrasound monitoring is a good candidate for
long-range passive tornado monitoring, especially in hilly terrain where
line-of-sight limits radar (e.g. Southeast United States). However, the
fluid mechanism(s) responsible for the infrasound must be identified to
enable researchers to interpret these currently unused signals. This is
the objective of the current research, which has used multiple
infrasound measurement modalities to identify correlations between
received infrasound signals and storm processes. This includes a fixed
infrasound array, a mobile infrasound array, and a single infrasound
microphone carried by a storm chaser. An overview of select events will
be presented, including measurements from an EFU tornado on 11 May 2017
that was within 20 km of the fixed array. These tornadic and
non-tornadic observations will then be used to identify potential
physical mechanisms.