Photo : Kari Saari

They resemble the layered clouds or sand dunes.

Finnish scientists have figured out how to appear unusual Aurora resembling layered clouds or sand dunes. This phenomenon is called the auroral dunes, was first recorded by Amateur astronomers in 2018. The study is published in the journal AGU Advances (translation

Aurora — glow of the upper atmosphere that occasionally arise in polar latitudes are the product of the interaction of Earth’s magnetosphere and solar wind — stream of plasma and charged particles that the Sun emits into space. In the ionized layer of the atmosphere — the ionosphere — these threads excite atmospheric atoms of oxygen and nitrogen, which begin to glow.

Choosing the photos for his book “Guide for observers of the Aurora”, Palmroth Minna (Minna Palmroth), Professor of the University of Helsinki have noticed that on some pictures, taken by Amateur photographers, glow has an unusual wavy form, reminiscent of layered clouds or sand dunes, and doesn’t fit any of the established categories of polar lights.

Palmroth engaged in computational physics of the cosmos and leads the research group developing the model of near-earth space. In particular she studies the Aurora Borealis, or, as scientists say, of auroral phenomena.

The Professor shared his discovery in a group on Facebook, and just a few days after the book launch, Amateur astronomers, again seeing the sky glow an unusual shape, reported the scientists.

The phenomenon was photographed in Ruovesi Laitila and in South-West Finland. Seven such events were recorded by the camera service Taivaanvahti (“sky watch”), the Finnish Association of Amateur astronomers.

Maxim Grandin (Grandin Maxime), one of the authors of the study, using astronomy program Stellarium determined the azimuth and elevation of stars behind the light. This allowed using the stars as reference points to calculate the height and length of auroral phenomena.

Scientists have found that the glow occurs at a height of from 80 to 120 kilometers. This part of the atmosphere are studied — to observe the region separating the electrically neutral part of the atmosphere from the ionosphere, is extremely difficult.

“Differences in brightness within the waves of “dune” can be caused either by wave-deposited particles, coming from outer space, or oxygen atoms in the atmosphere — presented in a press release of the University of the word Palmroth. — We believe that the “dunes” are the result of an increase in the density of oxygen atoms”.

The distance between crests of the dune — about 45 miles — scientists explain the presence in the mesosphere particular gravitational waves, creating heterogeneity in the distribution of oxygen atoms that, when faced with cosmic electrons begin to glow.

Gravitational waves caused by vibrations of the air that occur in the atmosphere due to the presence of irregularities on the surface of the Earth, rise to the level of the ionosphere through the so-called mesospheric holes, and then bend in the waveguide between the cold inversion layer on the bottom and menopausal top and begin to spread parallel to the earth’s surface.

The authors note that “dunes” are formed in the most difficult for atmospheric observations and are the result of a unique combination of processes related to solar activity and the flow of ions in the Earth’s atmosphere.

According to the authors, to describe these processes requires joint efforts of scientists who study the atmosphere and space.