Sound another secret of the Aurora
Dave Sullivan
Northern News Services
Yellowknife (Apr 18/01) - While we are concluding one of the best seasons for glimpsing the Northern lights, one mystery remains in the dark - what is the cause of the noise that occasionally accompanies the phenomenon?
Legend holds that whistling and crackling noise from Northern Lights are spirit voices that should be answered with whispers.
Problem is, so few have heard the lights make any noise that there are doubts in many circles. Despite experiments with sensitive microphones that can be compared to lost-cause searches for the Loch Ness Monster, aurora sounds have never been recorded.
Here's one good reason: the dancing lights form between 90 and 140 kilometres above Earth, where air is too thin to carry sound waves.
So is Doctor Tom Hallinan crazy? His colleagues don't think so, because the geophysics professor is a serious aurora scholar who's seen the lights from his Alaska lab countless times over a 35-year career in the North. One night he heard the sky make noise.
In the late 1960s "I was at on the Yukon River just above the Arctic Circle. I was walking outside coming back from dinner and the aurora brightened up. I was just enjoying it and then for a few seconds I heard it. It sounded like static but it was associated with what I was seeing."
Yellowknife tour guide Glen Walsh figures he's seen the Northern lights up to 500 times, but never heard them make even a peep.
"It's a great story if nothing else," is Walsh's response when asked if he believes they can make noise.
A lot of his customers ask him about the sound mystery.
Imaginary sounds
Theories explaining the phenomenon have been reduced to two. Either sounds are created closer to the ground by electrical fields creating static electricity, or the sounds are imaginary. Not real.
The second theory is explained by Jamie Jacobs of Yellowknife, who examined the mystery for a recent science fair project.
"If you're in a quiet area and you can't hear anything, your brain picks up the aurora's electrical impulses from what you see and interprets them as sound," the Grade 8 Range Lake school student said.
"It's your brain playing tricks on you."
She believes the static electricity theory "because that explains the swishing and the crackling sounds."
For her project, Jacobs e-mailed scientists at the Geophysical Institute at the University of Alaska. Almost 90 per cent of the institute's $25 million annual budget comes from the U.S. Defense department and NASA. The Fairbanks campus is home to the world's only university-owned rocket launch.
Auroral physicist Hans Neilsen based at the university doesn't go for the brain tricks theory either.
"I think we can rule that out because it makes things complicated," the Danish-born scientist says.
He doesn't doubt colleague Hallinan's claim and other stories about the lights making noise -- although it's very rare. Hallinan said the night he heard the lights, they were brighter than he'd ever seen.
"There's no real reason to doubt the truthfulness of all those people. It's sort of like theories about UFOs," Neilsen said.
Research in Scandinavia got close to showing that sound comes from the aurora's magnetic field after it reaches the ground, but no scientific paper was published.
Neilsen and others believe objects like pine cones and other pointy objects on the ground can receive static charges from the aurora, and that's where the noise comes from. Like the static discharge that can draw a spark and pop after walking across a carpet and touching metal.
Reports have reached scientists about a wide range of sounds from rustling paper, swishing, sizzling and crackling like radio static.
It is known the lights are caused by charged hot plasma winds from the sun colliding with Earth's magnetic field, but details beyond that are sketchy, Neilsen and Hallinan agree. Combined they have over 70 years experience staring at the Northern night sky, but still has no idea of things like how the aurora forms its shapes.
It may be comforting that parts of the aurora borealis remain mysterious, but other scientists looking for a breakthrough in fusion energy are unlocking more of its secrets.
The missing link
Just last week University of Maryland researchers announced that new satellite evidence reveals how the aurora reaches Earth so quickly after getting started with a massive magnetic storm 100,000 kilometres in space. The magnetic field snaps back and unleashes tens of thousands of trapped volts towards Earth.
The missing link turns out to be special 'whistler' waves that lock onto electrons and transfer energy almost at light speed.
