A new form of northern lights that appear across the sky in dune-like patterns has been discovered by a collaborative team of citizen scientists, photographers, and space physicists.
The celestial phenomenon wasn’t discovered until an amateur Facebook group of aurora borealis hobbyists noticed its pattern didn’t quite match up with other known forms of aurora. Each auroral form is like an atmospheric fingerprint, only formed by specific conditions in the atmosphere. Some take the shape of spanning arcs while others glow in ribbon-like patterns. As its name suggests, the green-tinged lights danced across the northern night skies like dunes spread across sandy beaches in a wave-like pattern. Shortly after this observation was made, a dune-like aurora appeared and was subsequently photographed in two different locations in southwest Finland.
Auroras are a product of solar wind, charged particles released from the Sun that flow toward Earth. When these particles reach Earth’s ionized upper atmosphere, the ionosphere, interactions between atmospheric oxygen and nitrogen atoms create disturbances that release light seen in auroral emissions. This activity makes studying the mesospheric environment challenging for satellites and other space instruments, which has limited research in this field. Measuring atmospheric phenomena is quite difficult at this altitude, which is why study author Minna Palmroth, professor of Computational Space Physics at the University of Helsinki, nicknamed it the "ignorosphere".
"One of the most unknowns is the interaction between the neutral atmosphere and the electromagnetic ionosphere. They often have different observational techniques, and one could, for example, observe one but not the other. The problem is that on the whole, it is so hard to measure, it is too high for radars and balloons, but too low for spacecraft," Palmroth told IFLScience, adding that scientists do not know how this region is constituted, the dynamics that occur in it, and what mechanisms are at play for atmospheric interactions.
Researchers were able to determine its altitude in the atmosphere based on the location of stars in the sky, as well as a little help from an astronomy program called Stellarium. The dunes were found to occur at a relatively low altitude of 100 kilometers (62 miles) in the upper parts of the third layer of the atmosphere, the mesosphere, and its bordering Mesopause. The aurora wavelength field measured about 45 kilometers long (28 miles).
For the first time, physicists observed mesospheric bores. This rare and little-studied phenomenon occurs in the auroral zone when gravity waves – a wave that organizes air into denser and "more tenuous" parts – born in the atmosphere begin to rise. Sometimes, very rarely, Palmroth explains that a gravity wave can be filtered when it is propagating upwards and becomes filtered between the mesopause and an inversion layer below. This inversion layer may bend the filtered waves and allow them to travel long distances horizontally. As it happens, these dunes are believed to occur in the same place where electromagnetic energy coming from space is transferred to the “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," said Palmroth. "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."
Discovering the new auroral form presents a novel way to investigate conditions in the hard-to-study upper atmosphere, note the researchers. However, Palmroth adds that the evidence is "circumstantial" and her team didn’t have spacecraft observations needed to rule out that the dunes are not due to waves in the precipitating electrons.