Did You Hear the Northern Lights?

Mark Thiessen, NGM staff

Next time you are lucky enough to witness an aurora borealis, you may want to also listen carefully for some faint applause. According to a new study announced this week, colorful displays of northern lights may actually produce audible clapping sounds. Finnish researcher Unto K. Laine from Aalto University has been studying the phenomenon for over a decade and believes that he has captured a distinct sound associated with intense episodes of northern lights.

Auroras occur when charged particles are thrown off the Sun as solar wind, then travel across interplanetary space, eventually interacting with the Earth’s magnetic field. This sets off the colorful displays.

There have been stories about an eerie noise associated with auroras for over a century at least, centered around the Arctic region where displays are more frequent and powerful. Most of these stories, however, have been considered just folklore and hearsay.

Many describe what they heard as being comparable to that of a radio left on a station that has gone off the air. Sort of a faint crackling or a hissing sound.

“In history there are thousands of relevant observations, but recordings also exist that consists of many different type sounds described by observers around the world such as crackling, clapping, popping, booms and low frequency noise,” says Laine.

In the new study, researchers set up three separate sites with highly sensitive microphones at the focus of parabolic dish antennae and recorded faint but distinct noises during some but not all intense geomagnetic activity.

“We found statistically significant correlations between sound pressure levels and geomagnetic activity in many different frequency bands,” says Laine.

 

 

There are a lots of ideas out there on what may be causing the sounds, with one theory saying that the culprit may be tree needles or pine cones—where there is a potential for an electrical gradient and a subsequent discharge.

The most popular hypothesis by far is the brush discharge mechanism in the atmosphere, says Laine, where geomagnetic storms may generate large charges in the atmosphere and these can suddenly get discharged with a clap sound.

He adds that while the scientific community has been left stumped as to how these noises could be produced, most sounds when they occur can be heard for a few minutes during a powerful display.

 

– The new study will be published in the proceedings of the 19th International Congress on Sound and Vibration.

 

 

Changing Planet

Andrew Fazekas, aka The Night Sky Guy, is a science writer, broadcaster, and lecturer who loves to share his passion for the wonders of the universe through all media. He is a regular contributor to National Geographic News and is the national cosmic correspondent for Canada’s Weather Network TV channel, space columnist for CBC Radio network, and a consultant for the Canadian Space Agency. As a member of the Royal Astronomical Society of Canada, Andrew has been observing the heavens from Montreal for over a quarter century and has never met a clear night sky he didn’t like.