Sound producing mechanism in temperature inversion layer and its sensitivity to geomagnetic activity

Sounds associated with aurora borealis, so called Auroral Sounds (AS), are explained by electrical discharges occurring in Temperature Inversion Layer (TIL) approximately 75 meters above the ground. It is assumed that under favorable weather conditions the number of AS events depends on the activity of the geomagnetic (GM) storm. The historical testimonies of AS indicate that the GM storm should be strong enough to rise the bright and lively auroras to the zenith before these sounds can be observed. The goal of this study is to test the relevancy of this claim by studying the sensitivity of the AS producing mechanism under a moderate GM activity. A four-hour long period of the sound measurements done around the local magnetic midnight Jan 25–26, 2022 at Fiskars village, Finland, is analyzed. Sixty AS event candidates were
manually selected and their temporal distribution and period histogram constructed for statistical comparisons with the GM data measured simultaneously by the Finnish Meteorological Institute (FMI) at
Nurmijärvi Geophysical Observatory (NGO). The data was also used for regression models to study possible causal relationship between the GM activity and the AS events. A strong causality between the GM activity and the AS events was found. The sounds were predicted by the GM activity with 90% accuracy after a delay of 21 min. The results show that the AS events are much more common than previously thought.