The auroras have long captivated the public and experts alike. In fact, the astronomer Galileo Galilei coined the term in Latin. Auroras occur when charged particles, such as electrons, are expelled by the sun and channeled toward the poles of the Earth by the magnetic field of our planet. There they interact with the gases in the atmosphere, increasing their energy and subsequently released as light.
If the northern lights have been seen in many forms, including “silent arches”, spirals and crowns, now, thanks to the work of a group of enthusiastic hobbyists and scientists, we have a previously unknown shape, a pattern that resembles the sand dunes.
That’s how it is. Like sand dunes, this new form of aurora is caused by waves of oxygen flowing through a stream of solar particles. The light show is uniformly tinted green and stretches for more than 30 miles and nearly 100 miles, in the mesosphere.
His discovery was, as is sometimes the case in science, by chance. Space physicist Minna Palmroth of the University of Helsinki, Finland, who leads a research group developing the world’s most accurate simulation of space and near-Earth space weather that cause auroral emissions, asked a team of auroral observers to send you pictures for a book. One of them highlighted images of a particular aurora that didn’t seem to fit any known type and called them simply ‘auroral dunes’.
Atmospheric fingerprint
Each auroral shape is like an atmospheric fingerprint, formed by specific conditions in the atmosphere . As the name suggests, green-tinged lights danced in the northern sky like dunes stretched across sandy beaches in a rippling pattern. Shortly after a similar aurora appeared and was subsequently photographed at two different locations in southwestern Finland.
Experts traced its origin to a waveguide formed within the mesosphere and its boundary, the Kármán line. The study also posits that this new form of aurora provides researchers with a renewed way to investigate the qualities of the upper atmosphere.
Maxime Grandin, a postdoctoral researcher in the Palmroth team, identified the stars after emission and determined the azimuths and elevations of the stars with the help of the astronomy software program Stellarium , which made it possible to use the stars as reference points when calculating the altitude and extent of the aurora. The team detected a total of seven similar ‘auroral dune ‘ events and a camera recorded the same uniform wave pattern across all of them.
“The waves have different frequencies, different wavelengths, different amplitudes and thus observing something very uniform, like the dunes, means that there has to be some active mechanism that makes them so uniform”, clarifies Palmroth.
What can cause this shape?
Palmroth explained that the mechanism could be an unusual event called a mesospheric hole , whereby a particular wave is filtered and bent, allowing it to travel horizontally between two layers in the atmosphere. The phenomenon – rare and little studied – is similar to a rising tide that forms a wave in a river. According to the expert, this can happen when, unusually, the temperature of one layer of the atmosphere is slightly higher than the two layers above and below. The aurora dune appearance, according to the team, is due to the wave that produces peaks and valleys in oxygen density.
With the help of measuring devices controlled by the Finnish Meteorological Institute, they discovered that dunes occur simultaneously and in the same region where electromagnetic energy originating from space is transferred to the “ignorosphere” (humorous nickname among scientists to refer to the mesosphere).
“This could mean that the energy transmitted from space to the ionosphere may be linked to the creation of the inversion layer in the mesosphere,” says Palmroth. “In terms of physics, this would be a surprising discovery, as it would represent a new and previously unobserved mechanism of interaction between the ionosphere and the atmosphere.”
Obstacles in the way
The part of the auroral zone where Earth’s electrically neutral atmosphere meets the edge of space is an extremely challenging environment for satellites and other space instruments. That is why it is one of the least studied places on our planet. Altitude is a problem. The interaction between the neutral atmosphere and the electromagnetic ionosphere has different observation techniques but the biggest obstacle is that it is too high for radars and balloons and too low for spacecraft.
Referencia: Citizen scientists discover a new auroral form: Dunes provide insight into the upper atmosphere” by M. Palmroth, M. Grandin, M. Helin, P. Koski, A. Oksanen, M. A. Glad, R. Valonen, K. Saari, E. Bruus, J. Norberg, A. Viljanen, K.4 Kauristie, and P. T Verronen. AGU Advances 1, 1-12, xx.1.2020. DOI: 10.1002/aga2.20017
