The aurora borealis – the dazzling lights formed as electrically charged particles released from the sun enter the Earth’s atmosphere and collide with gases such as oxygen and nitrogen – have long fascinated scientists and photographers alike. While scientists provide the explanations desired by photographers, the photographers are now giving something back.
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As part of her work, Minna Palmroth, professor of computational space physics at the University of Helsinki, decided to compile thousands of photographs taken by amateur aurora watchers into a book. During the process, she was alerted by these hobbyists that a certain auroral form did not fit into any of the pre-existing categories. Rather than the familiar vertical bands of light, the form appeared as a green-tinged and even pattern of horizontal waves resembling dunes on a sandy beach. Logically, the phenomenon was named ‘the dunes’.
What particularly fascinated the Helsinki researchers was the fact that the auroral dunes were found to occur at an altitude of 100 kilometres, in the upper parts of the portion of the Earth’s atmosphere known as the mesosphere. This layer – where Earth’s atmosphere meets the edge of space – is an extremely difficult environment to study. While most planes can’t fly so high, satellites orbit higher.
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According to Palmroth, this part of the atmosphere is one of least studied places on our planet. ‘Due to the difficulties in measuring the atmospheric phenomena occurring between 80 and 120 kilometres in altitude, we sometimes call this area the ignorosphere,’ she said in a statement. The new discovery could provide a way to learn more about this neglected region.
In an accompanying study, the researchers suggested that the dunes occur as a result of a ‘mesospheric bore’, a rare and little-studied phenomenon that occurs when gravitational waves rise upwards and collide with the electrons precipitating down upon the atmosphere from space. This collision creates auroral light.
Prior to this study, mesospheric bores were not observed in the auroral zone and the discovery points towards an interaction between the atmosphere and space not previously understood. While researchers specialising in the two fields have largely investigated their topics separately, this discovery could bring them closer together.
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