Generation of Infrasound by Evaporating Hydrometeors in a Cloud Model

Abstract

The dynamical core of the Regional Atmospheric Modeling System has been tailored to simulate the infrasound of vortex motions and diabatic cloud processes in a convective storm. Earlier studies have shown that the customized model (c-RAMS) adequately simulates the infrasonic emissions of generic vortex oscillations. This paper provides evidence that c-RAMS accurately simulates the infrasound associated with parameterized phase transitions of cloud moisture. Specifically, analytical expressions are derived for the infrasonic emissions of evaporating water droplets in dry and humid environments. The dry analysis considers two single-moment parameterizations of the microphysics, which have distinguishable acoustic signatures. In general, the analytical results agree with the numerical output of the model. An appendix briefly demonstrates the ability of c-RAMS to accurately simulate the infrasound of the entropy and mass sources generated by an equilibrating cloud of icy hydrometeors.

Measurement and characterization of infrasound from a tornado producing storm

“…The low frequency signal was assumed to be mostly due to wind noise, but there was sufficient coherence for successful beamforming to produce bearings to the tornado producing storms. This lower frequency signature has had several proposed mechanisms including radial oscillations (Abdullah, 1966;Bedard, 2005;Schecter, 2012), electromagnetic sources (Balachandran, 1983;Few, 1985;Pasko, 2009), co-rotating vortices (Powell, 1964;Georges, 1976), vortex-surface-interactions (Tatom et al, 1995), heat-related sources (Nicholls et al, 2004;Akhalkatsi & Gogoberidze, 2009;Schecter & Nicholls, 2010;Markowski & Richardson, 2010;Schecter, 2012), and non-equilibrium effects (Zuckerwar & Ash, 2006;Ash et al, 2011).…”

“…In addition, the frequencies of the current and previous observations were too high for those predicted based on co-rotating vortices, and the original postulate that motivated this mechanism has been disproven. 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).…”

“…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.…”

Acoustic detection, tracking, and characterization of three tornadoes

“…For example, three dimensional Rossby waves can radiate from the vortex if the maximum wind speed of the vortex exceeds a modest threshold (Schecter et al, 2008), and adiabatic processes involving hail and moisture evaporation/ condensation are likely sources within the supercell Gogoberidze, 2009, 2011;Schecter, 2011b;Schecter and Nicholls, 2010). However, periodic vortex expansion and contraction is not likely to be a source of infrasound (Schecter, 2011a).…”