Measurement and characterization of infrasound from a tornado producing storm

TL;DR

This study measures and characterizes infrasound signals associated with a tornado-producing storm, revealing specific frequency patterns and temporal persistence of infrasound features before, during, and after tornadogenesis.

Contribution

It provides detailed infrasound measurements linked to tornado activity, demonstrating the potential for infrasound to monitor storm evolution and tornado formation.

Findings

Elevated infrasound levels precede tornado by 7 minutes.

A fundamental infrasound frequency at ~8.3 Hz was identified during the tornado.

Spectral peaks persisted from 4 minutes before to 40 minutes after tornadogenesis.

Abstract

A hail-producing supercell on 11 May 2017 produced a small (EFU) tornado near Perkins, Oklahoma (35.97, -97.04) at 2013 UTC. Two infrasound microphones with a 59-m separation and a regional Doppler radar station were located 18.7 km and 70 km from the tornado, respectively. Elevated infrasound levels were observed starting 7 minutes before the verified tornado. Infrasound data below ~5 Hz was contaminated with wind noise, but in the 5-50 Hz band the infrasound was independent of wind speed with a bearing angle that was consistent with the movement of the storm core that produced the tornado. During the tornado, a 75 dB peak formed at ~8.3 Hz, which was 18 dB above pre-tornado levels. This fundamental frequency had overtones (18, 29, 36, and 44 Hz) that were linearly related to mode number. Analysis of a larger period of time associated with two infrasound bursts (the tornado occurred during the first event) shows that the spectral peaks from the tornado were present from 4 minutes before to 40 minutes after tornadogenesis. This suggests that the same geophysical process(es) was active during this entire window.