The sounds of the Northern Lights have been a mystery to scientists for over a century. But now it seems that a researcher has figured out how auroras (极光) really make sounds. "It has pretty much been confirmed all over the world," "historian Fiona Amery said. "In Canada, Norway and Russia, they are all hearing very much the same sounds." "The auroras can occur hundreds of kilometers above the ground, which strengthens opinions that their sounds are just a false impression," said Fiona. Many scientists argued that auroras were too far away to hear and that any sound would take several minutes to reach the ground, so it was impossible for them to change in time with the auroras.
However, other scientists were convinced that the Northern Lights really made noises. In the 1920s, Canadian astronomer Clarence Chant first suggested a mechanism by which they could occur: The motion of the aurora caused changes in the electrification of the atmosphere that created crackling sounds close to the ground. Almost 100 years later, Clarence's suggestion seems close to what could be the true reason for the sounds.
In 2012，an expert named Unto Laine showed a recording of auroral sounds after years of monitoring auroras. In 2016, he announced the mechanism that makes the sounds: an inversion layer(逆温层) of cold air in the atmosphere that can form below an aurora and a short distance above the ground in calm weather.
Unto argues that visible changes in the aurora cause changes in the inversion layer, causing accumulated electricity to discharge as sparks (火花) that create sounds that can be heard. That explains how the sounds correspond with the aurora 's visible movements 一they begin to happen in the inversion layer only about 75 meters above the observer.
