For centuries, legends spread of the aurora "speaking" and making sounds as geomagnetic storms glimmer over the Earth's poles.
Scientists dismissed these as psycho-acoustic phenomena for a long time — imagined sounds that don't really exist. Then, in 2012, a group of researchers from Aalto University, Finland, proved the source of this sound.
A new study by these researchers highlights the strong link between geomagnetic fluctuations and "auroral sounds", a report from Forbes explains. It also shows that these sounds can be predicted with incredible accuracy.
Recording the aurora
The Aurora Borealis and Aurora Australis (northern and southern lights) are caused by the solar wind, charged particles from the Sun, interacting with the Earth's magnetic field. Those striking green waves of color are generated when the charged solar particles collide with molecules of oxygen traveling at incredibly high speeds through the atmosphere.
In their new study, the Aalto University researchers describe how, under the right conditions, a pocket of warm air roughly 75 meters above the ground can hold a static charge that discharges when the air dissipates, letting off a crackling sound. The researchers explain this sound is likely to occur when the aurora is present, though it can also happen when they are not visible, depending on the geomagnetic conditions.
"This cancels the argument that auroral sounds are extremely rare and that the aurora borealis should be exceptionally bright and lively," explained Unto K. Laine, Professor Emeritus at Aalto University and lead author of the new paper, which was first presented at the Baltic Nordic Acoustic Meeting in Aalborg, Denmark.
For their investigation, the researchers recorded four hours of auroral sounds from a point near the village of Fiskars, Finland, roughly 56 miles (90 kilometers) west of Helsinki. Though no northern lights were present during the recording, the Finnish Meteorological Institute data showed that geomagnetic activity was similar to the conditions that would usually light up the sky when the sounds were taking place.
'Auroral sounds' are more common than previously thought
There was such a strong correlation between the sounds and the geomagnetic activity, in fact, that the researchers believe they can now accurately predict when the aurora will make a sound. "Using the geomagnetic data, which was measured independently, it’s possible to predict when auroral sounds will happen in my recordings with 90%percent accuracy," Laine said.
Laine also explained that these sounds are much more common than previously thought, though most of the time someone hears them, they assume it's ice cracking or a nearby animal standing on a twig.
The new research means that the next wave of tourists to travel for the northern lights between September and March may also be looking out for sounds and the incredible sights overhead.
Though most of those travelers will undoubtedly have a fantastic experience, it's unlikely any of them will get close to the experience of the SpaceX Crew-2 astronauts who recently flew over an aurora before landing back on Earth. Adding to the Aalto University team's research, NASA will also soon launch two rockets into the northern lights as part of its Ion-Neutral Coupling during Active Aurora (INCAA) mission in a bid to better understand the phenomena.
Editor's note 7/6/22: An older version of this article didn't mention the Aalto University researchers' early published work on auroral sounds. This has been added to the article.