Infrasound generation by tornadic supercell storms

Abstract

Acoustic wave generation by turbulence in a stratified, moist atmosphere is studied. It is shown that, in saturated moist air turbulence, in addition to the Lighthill's quadrupole and dipole sources of sound (related to stratification and temperature fluctuations), there exist monopole sources related to heat and mass production during the condensation of moisture. We determine the acoustic power of these monopole sources and show that this radiation is dominant for typical parameters of strong convective storms. The results are in good qualitative agreement with the main observed characteristics of infrasound radiation by strong convective storms, e.g. total acoustic power and characteristic frequency.

Measurement and characterization of infrasound from a tornado producing storm

“…Recent simulations (Schecter & Nicholls, 2010;Schecter, 2012) show that there is a lack of discernible infrasound in the absence of latent-heating effects and that non-tornadic thunderstorm cells produce infrasound from the melting level. This suggests that latent heat sources are a likely mechanism, and simulations of the liquid-vapor transitions within a cloud were able to produce infrasound between 0.1 and 10 Hz (Akhalkatsi & Gogoberidze, 2009;Schecter & Nicholls, 2010). However, radial vortex oscillations including the non-columnar nature of a tornado (Schecter, 2012) and analysis incorporating nonequilibrium effects (Zuckerwar & Ash, 2006;Ash et al, 2011) are also consistent with observations.…”

Spectrum of infrasound radiation from supercell storms

“…(16) represent well known sources of sound: the first term represents Lighthill's quadrupole source (Lighthill, 1952); the second term is a dipole source related to temperature fluctuations (Goldstein, 1976); S γ is a monopole source related to variability of adiabatic index and usually has negligible acoustic output (Howe, 2001). As it was shown in Akhalkatsi and Gogoberidze (2009), in the case of saturated moist air turbulence there exists two additional monopole sources of sound, S q and S m , related to nonstationary heat and mass production during condensation of moisture, respectively.…”

“…As shown by Akhalkatsi and Gogoberidze (2009), the peak frequency of acoustic radiation is inversely proportional to the turnover time of energy containing turbulent eddies ν peak ∼ v 0 /l, whereas total acoustic power is proportional to v 4 0 , ∆T 4 and inversely proportional to l.…”

“…Broad and smooth spectra of observed infrasound radiation indicates that turbulence is a promising sources of the radiation. Acoustic radiation from turbulent convection was studied by Akhalkatsi and Gogoberidze (2009) taking into account effects of stratification, temperature fluctuations and moisture of air, using Lighthill's acoustic analogy. It was shown for typical parameters of strong convective storms, infrasound radiation should be dominated by a monopole acoustic source related to the moisture of the air.…”

Generation of Infrasound by Evaporating Hydrometeors in a Cloud Model

“…However, entropy and mass fluctuations associated with phase transitions may also contribute. A recent analytical study concluded that such fluctuations in the moist turbulence of a severe storm are likely to dominate other sources of 0.1-Hz infrasound (Akhalkatsi and Gogoberidze 2009).…”