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The mysterious sound of the aurora

  Anyone who sees the phenomenon of aurora on TV for the first time will surely ask, “Is this really not a movie special effect?” “Does such a magical scene really exist in the real world?” People may ask, “What the hell, what’s the sound?”
  Aurora is a plasma phenomenon formed by charged particles from the sun or the Earth’s magnetosphere entering the Earth’s magnetic field at high altitudes near the north and south poles. The charged particles cause molecules or atoms in the upper atmosphere to excite produced. Whether the aurora will make a sound has always been a topic of debate in the academic circles.
endless guesswork

  In the early decades of the 20th century, witnesses reported that the Northern Lights appeared with a barely perceptible crackling or swishing sound; in the 1930s, newspapers in the Shetland Islands published eyewitness accounts of the Aurora Borealis. Descriptions of the Northern Lights, “silk-like rustling” and “slamming two wooden boards together”; in addition, people in northern Canada and Norway have also reported hearing the sound of the aurora.
  According to two astronomers’ assistants who claimed to “hear the aurora”, the aurora sound was similar to “a very strange faint whistle with distinct fluctuations that seemed to coincide exactly with the vibrations of the aurora”; and “burning grass” or spray”. But neither mentioned the aurora’s sound mechanism.
  The vast majority of scientists do not believe their claims. A few scientists believe that the probability of “aurora sound” is closely related to the altitude measurement density of auroras, and only those auroras that appear lower in the atmosphere can emit sounds that can be picked up by the human ear. However, according to records from 1932 to 1933, auroras occurred most often at a height of 100 kilometers above the earth, and those below 80 kilometers were quite rare, and the identifiable sound emitted at an altitude of 100 kilometers could not reach the ground. of.
  Physicists and meteorologists believe that the so-called “sound of aurora” is actually a folklore or an auditory illusion. According to British physicist Sir Oliver Lodge, the aurora is a very vivid phenomenon, and the person who witnesses the spectacle may experience a psychological phenomenon, similar to the “swishing sound in the brain” when watching meteors .
  In 1923, the Canadian astronomer Clarence Chant first tentatively proposed the “aurora sound”, he believed that the movement of the northern lights changed the earth’s magnetic field, causing the atmosphere to electrify, even at considerable distances, when the electrification process When encountering a ground object, it produces a crackling, static-like sound closer to the surface. This can happen to the observer’s clothing, as well as to objects around him. This seems to support Chant’s point in some way, as some “Aurora Sound” sightings mention “ozone odors,” a metallic odor similar to electric sparks.
  It wasn’t until the 1970s, after reexamining by two auroral physicists, that Chant’s view gained traction. However, the mechanism of this sound generation has not been reasonably explained, so Chant’s point of view is still controversial.

Reasonable explanation

  In 2012, Professor Ryan, an acoustic engineer at Aalto University in Finland, and his colleagues finally rationalized the source of the mysterious sound of the Northern Lights – there is evidence that this sound is produced at a low altitude of 70 meters above the ground; The gorgeous and unpredictable Northern Lights are produced at an altitude of 120 kilometers above the ground.
  In order to find the source of the sound, the scientists recorded the sound of the Northern Lights at the observation point using three independent microphones. These sounds were then compared and analyzed, and the source of the Northern Lights sounds was finally determined. When the aurora borealis appeared at the observation point, the Finnish Meteorological Institute also simultaneously measured the geomagnetic disturbance associated with the aurora borealis.
  In 2016, Lane published a paper linking recordings of crackling and popping sounds during auroras to temperature profiles measured by the Finnish Meteorological Institute. These data not only prove that the appearance of these sounds is related to the aurora, but also that the sound is produced by discharges in the inversion layer about 70 meters above the ground.

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