Northern Lights resembling sand dunes discovered by amateur photographers: 'Will help study upper atmosphere'

The phenomenon is believed to be caused by waves of oxygen atoms glowing due to a stream of particles released from the Sun


                            Northern Lights resembling sand dunes discovered by amateur photographers: 'Will help study upper atmosphere'
(Kari Saari)

A new type of aurora — more commonly known as the Northern Lights or the Southern Lights — has been discovered. Shaped like dunes, the new form was identified —all thanks to a collaboration between aurora-hunting Finnish amateur photographers along with professional space researchers.

Since the discovery of new types of the aurora is rare, this one highlights the importance of citizen scientists, say experts.

The aurora form when electrically charged particles collide with the gases in our upper atmosphere. The charged particles, accelerated into our atmosphere by the Earth’s magnetic field, transfer their energy to the atmospheric gases. This extra energy is released in the form of light, forming the majestic aurora

Named "dunes" as the undulations reminded observers of sand formations, the new phenomenon is believed to be caused by "waves of oxygen atoms glowing due to a stream of particles released from the Sun," say researchers in their findings published in AGU Advances.

The origins of the dunes were tracked to a waveguide formed within the mesosphere and its boundary, the mesopause. The study also posits that this new auroral form provides researchers with a new way to investigate conditions in the upper atmosphere.

“Auroral forms are like fingerprints linking optical features to physical phenomena in the near‐Earth space. While discovering new forms is rare, recently, scientists reported of citizens' observations of STEVE, a pinkish optical manifestation of subauroral ionospheric drifts that were not thought to be visible to the naked eye. We have presented a new auroral form consisting of regular wave forms we call the dunes, which to our knowledge have not been reported before in scientific literature. On 7 October 2018, citizen observers took multiple digital photographs of the same dunes simultaneously from different locations in Finland and Sweden,” says the team. 

Auroral dunes captured on October 7, 2018, in Laitila. The dunes are marked by magenta circles and numbers. (b) Simultaneous picture of the dunes in Ruovesi, 172 km northeast from Laitila (AGU Advances)

Before this discovery, mesospheric bores were not observed in the auroral zone, nor have they been investigated via auroral emissions, say experts.  "One of the most memorable moments of our research collaboration was when the phenomenon appeared at that specific time and we were able to examine it in real-time," says Northern Lights and astronomy hobbyist Matti Helin in the analysis.

The observations

Minna Palmroth, Professor of Computational Space Physics at the University of Helsinki, heads a research group that develops the world's most accurate simulation of the near-Earth space and space weather that causes auroral emissions. 

“The Sun releases a steady flow of charged particles known as the solar wind. Reaching the Earth's ionised upper atmosphere, the ionosphere, they create auroral emissions by exciting atmospheric oxygen and nitrogen atoms. The excitation state is released as auroral light,” says the study.

In late 2018, Palmroth published a book, which was a result of her cooperation with Northern Lights enthusiasts and the answers she provided to questions about the physics of the phenomenon in the hobbyists' Facebook group.

Thousands of magnificent photographs of the Northern Lights taken by hobbyists were surveyed and categorized for the book. During the classification, hobbyists pointed out that a certain auroral form did not fit into any of the pre-existing categories. 

Days after the book was published, the hobbyists saw this unusual form again and immediately informed Palmroth.  The form appeared as a green-tinged and even pattern of waves resembling a striped veil of clouds or dunes on a sandy beach. 

Accordingly, investigations into the phenomenon were launched, with hobbyist observations and scientific methods coming together to explain the waves. Each day, the team found new images and came up with new ideas, eventually getting to the bottom of it. 

The phenomenon was photographed at the same time in both Laitila and Ruovesi, southwest Finland, with the same detail observed in the auroral emission in both images. 

Maxime Grandin, a postdoctoral researcher in Palmroth's team, found that the auroral dunes occur at a relatively low altitude of 100 km in the upper parts of the mesosphere. The wavelength of the wavefield was measured to be 45 km.

A total of seven similar events — where a camera had recorded the same even pattern of waves — were further identified from the Taivaanvahti (Sky Watch) service maintained by the Finnish Amateur Astronomer Association, Ursa.

Citizen scientist photographs are becoming accurate enough for scientific investigations, say experts (Getty Images)

"The phenomenon in question is a mesospheric bore, a rare and little-studied phenomenon that takes place in the mesosphere. The tidal bore phenomenon is a wave common to many rivers, where the tide travels up the river channel,” adds the study. 

According to researchers, the paper adds to the growing body of work that illustrates the value of citizen scientist images in carrying out a quantitative analysis of optical phenomena. 

“It is clear that the citizen scientist photographs are becoming accurate enough for scientific investigations. Further, the dune project presents means to create a general interest in physics, emphasizing that citizens can take part in scientific work by helping to uncover new phenomena,” say experts.

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