Scientists at Aalto University using microphones determined the crackles or muffled bangs are formed about 230 feet above ground level.
"Our research proved that, during the occurrence of the northern lights, people can hear natural auroral sounds related to what they see," Aalto researcher Unto K. Laine said.
Laine said researchers suspect there may be several mechanisms behind the formation of auroral sounds, but they are "likely caused by the same energetic particles from the sun that create the northern lights far away in the sky."
"These particles or the geomagnetic disturbance produced by them seem to create sound much closer to the ground," he said in a university release Monday.
Much about the auroral sounds is still a mystery, researchers said, as they do not occur regularly when the northern lights, also known as aurora borealis, are seen.
They are so soft it is difficult to hear them and to distinguish them from ambient noise, the release said.
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