Image: © surangaw/Stock.adobe.com
The famous Northern Lights has just added a new string to its bow following the discovery of a whole new form of phenomenon.
One of the greatest treats for stargazers has just gotten a whole lot better. This comes after the discovery of a new type of auroral form in the Northern Lights by a group of Finnish amateur photographers.
The Northern Lights originate from a steady flow of charged particles brought to Earth by solar wind. When it hits the planet’s ionised upper atmosphere, oxygen and nitrogen atoms become excited, releasing auroral light.
Named ‘dunes’ by the hobbyists, this peculiar new phenomenon is believed to be caused by waves of oxygen atoms glowing due to a stream of particles released from the sun. In a paper published to AGU Advances, physicists from the University of Helsinki looked at dunes in greater detail. They are part of a group developing some of the world’s most accurate simulation of the near-Earth space and space weather that creates auroras.
A chance discovery
This latest discovery came after a book called Revontulibongarin opas (‘A guide for aurora borealis watchers’) categorised thousands of photographs of the Northern Lights taken by hobbyists.
However, during the classification, hobbyists pointed out that a certain auroral form did not fit into any of the pre-existing categories. By sheer coincidence, hobbyists saw the unusual aurora form again a few days after it was published and immediately informed the book’s author, Minna Palmroth, who also heads the group at the University of Helsinki.
The auroral dunes have been seen occurring several more times in follow-up observations at a relatively low altitude of 100km in the upper parts of the mesosphere. The wavelength of the wave field was measured to be 45km.
Palmroth said the part of the auroral zone where the Earth’s phenomenon occurs is an extremely challenging environment for satellites and other space-borne instruments.
‘The ignorosphere’
“Due to the difficulties in measuring the atmospheric phenomena occurring between 80km and 120km in altitude, we sometimes call this area ‘the ignorosphere’,” she said.
“The differences in brightness within the dune waves could be due to either waves in the precipitating particles coming from space, or in the underlying atmospheric oxygen atoms. We ended up proposing that the dunes are a result of increased oxygen atom density.”
The study suggested that the phenomenon is a mesospheric bore, a rare and little-studied phenomenon that takes place in the mesosphere. Until this latest discovery, mesospheric bores haven’t been seen in the auroral zone, nor have they been known to have links to auroral emissions.
The dunes occur simultaneously in the same region where electromagnetic energy from space is transferred to the so-called ignorosphere.
“This could mean that the energy transmitted from space to the ionosphere may be linked with the creation of the inversion layer in the mesosphere,” Palmroth said. “In terms of physics, this would be an astounding discovery, as it would represent a new and previously unobserved mechanism of interaction between the ionosphere and the atmosphere.”
