IN SPACE – SEPTEMBER 9: (EDITORIAL USE ONLY) In this handout photo provided by the European Space … [+]
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Can the aurora “talk?”
If you stand outside under a clear sky while a geomagnetic storm rages above you the sounds you’re most likely to hear are happy ones from other northern lights-chasers. However, aside from the odd “wow” and the clicking of camera shutters there have for centuries been myths and legends that the aurora itself makes a sound.
Suggestions that the aurora—which occur in Earth’s ionosphere hundreds of miles up—come with a whistle or whizz, a crackle or hiss, can be found in accounts from Greenland, the Shetland Islands, northern Canada and Norway. “As if two planks had met flat ways—not a sharp crack but a dull sound, loud enough for anyone to hear,” according to one account.
Dismissed as psycho-acoustic phenomena—science-speak for “you’re imagining it”—new recordings from Aalto University in Finland suggests that there is a strong link between geomagnetic fluctuations and “auroral sounds.”
The northern (and southern) lights are caused by the solar wind in space —charged particles from the Sun—being accelerated down the field lines of the Earth’s magnetic field. Green lights are caused by the charged particles colliding with molecules of oxygen, while the other colors by nitrogen molecules.
It’s proposed that when the circumstances are just right it’s possible for a pocket of warm air around 75 meters above the ground to hold a trapped static charge that discharges when the air dissipates. Cue an occasional crackle or pop.
It’s tied to the geomagnetic conditions, so linked to the aurora, but the sound can occur even when aurora aren’t visible. That was a surprise because legends have always associated only strong, lively displays of the northern lights directly above the observer with sounds.
“This cancels the argument that auroral sounds are extremely rare and that the aurora borealis should be exceptionally bright and lively,” said Unto K. Laine, Professor Emeritus at Aalto University and lead author of a new published paper presented at the Baltic Nordic Acoustic Meeting in Aalborg, Denmark.
Laine made four hours of recordings of auroral sounds close to the village of Fiskars, Finland about 56 miles/90 kilometers west of Helsinki.
There were no northern lights displays that night, but when the sounds on the recordings were compared with measurements of geomagnetic activity by the Finnish Meteorological Institute there was a strong correlation. According to the paper the 60 best candidate “auroral sounds” were all linked with changes in the geomagnetic field.
The correlation was so precise that Laine thinks he can now predict when the northern lights 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% accuracy,” said Laine. “The sounds are much more common than anyone thought, but when people hear them without visible aurora, they think it’s just ice cracking or maybe a dog or some other animal.”
Could there now be a boom in people traveling north not only to see the aurora, but also the hear it?
“It’s interesting because if you look at myths from Greenland about the northern lights they involve a whistling or crackling sound … there was a strong feeling that the aurora could speak,” said Tom Kerss, author of Northern Lights: The definitive guide to auroras and not involved with this research. “But it’s the white whale of aurora chasing—I’ve never heard it.”
The northern lights occur as an auroral oval around the North Pole at about 66-69° North latitudes—the Arctic Circle. The best places to see them are Alaska, northern Canada, Iceland, Greenland, Norwegian Lapland, Swedish Lapland, Finnish Lapland and northern Russia.
Northern lights “season” is September through March, though only because it’s now not getting dark above the Arctic Circle, where they mostly occur continuously. However, you may still be able to hear them …
Wishing you clear skies and wide eyes.
