Does the Aurora Borealis Make a Sound?


If you want to hear the aurora sound, listen on a calm, clear night. (Luke Stackpoole)

If you want to hear the aurora sound, listen on a calm, clear night. (Luke Stackpoole)

Do the Northern Lights or aurora borealis make a sound? The answer is yes. However, not everyone hears the sound and not all aurora produce it.

Eyewitness Accounts of the Aurora Sound

Several credible witnesses in both the Northern Hemisphere (aurora borealis) and Southern Hemisphere (aurora australis) report hearing a sound accompanying the Northern Lights and Southern Lights.

According to Neal Brown, former director of the Poker Flat Research Range, which conducts extensive experiments on the aurora borealis, witnesses say they hear the sound of the aurora when it is visible. Since the lights we see from the aurora are produced at 60 miles (100 kilometers) and higher up in the atmosphere, it’s unlikely the sound is coming directly from the aurora. This is simply because the light reaches an observer much faster than any sound. However, the reports of sounds, usually described as a hissing or crackling, are credible. Certain blindfolded subjects, unable to see the aurora, correctly announced the presence of the aurora, based on sound. Not everyone hears the aurora, plus it seems likely the conditions aren’t right for all aurora to produce the sound. The sound has been reported in both summer and winter, on a variety of terrains.

Detection and Explanation

Although it doesn’t seem likely sounds emanate directly from the aurora, scientists have tried to detect it. For the most part, instruments directed at the aurora have failed to identify any sound or noise. However, the aurora do emit radiation. Some of this is visible light, plus there is ultraviolet light, infrared radiation, and a few x-rays. The electromagnetic field might conceivably cause a sound to be produced by ice crystals or vegetation or stimulate a response in the body that the brain perceives as sound.

In 2012, Professor Unto K. Laine of Aalto University in Finland and his team detected and pinpointed aurora sounds. Using data provided by the Finnish Meteorological Institute, Laine proposed an inversion layer hypothesis to explain the sound. According to this hypothesis, crackling and popping sounds are discharges (sparks) released when a geomagnetic storm activates electrical charge accumulated in an atmospheric inversion layer. The hypothesis explains why aurora sounds are only heard when weather is calm, because even slight wind can prevent an inversion layer from forming.

Laine’s team detected aurora sounds above tree tops, at and above a height of 70 meters (230 feet) above the surface. The loudest sounds occurred around 75 meters (250 feet), which is the altitude of most inversion layers. This makes sense because pointy objects, like pine trees and pine cones, provide an optimal surface for an electric discharge.

Have you heard the aurora or are you interested in reading about the experiences of other people? Here’s your chance to report the experience.

References

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