Infrasound emissions from tornadoes and severe storms compared to potential tornadic generation mechanisms

Abstract

Infrasound emitted by tornado-producing storms has been observed before tornadogenesis, and can be detected beyond line-of-sight due to low atmospheric attenuation. Therefore, passive infrasound monitoring shows potential for the study and prediction of tornadoes, provided received infrasound signals can be correlated to the tornado flow-field. Herein, observations of atmospheric infrasound during four severe storms are reported briefly. The storms were selected as a sample of severe weather; two produced tornadoes, one produced merely a funnel cloud, and the last was a hail storm with no significant rotation. In general, the observations are in agreement with previous literature indicating that tornadoes cause increased infrasound levels between 0.5 Hz and 10 Hz. However, the underlying physical mechanism responsible for tornado infrasound emissions remains elusive. Thus, this paper presents a review of postulated mechanisms for meteorological infrasound, which are evaluated in light of the reported storms. Electromagnetic sources are discounted due to their impulsive nature. Co-rotating vortex models and vortex-seismic coupling are similarly rejected. Due to its previous success, turbulent jet noise is considered a likely mechanism, though in the audible range. Finally, radial vortex vibrations, latent-heat effects, and non-equilibrium effects are all considered possible mechanisms in light of available observations.