In regions like Scandinavia and Alaska, colorful lighting effects in the sky are not uncommon. Nevertheless, this aurora is something very special: it is a previously completely unknown Aurora variant.
Greenish veils that are strikingly flat and interspersed with regular ripples – this is what the new aurora looks like that Minna Palmroth of the University of Helsinki and her colleagues have now discovered when evaluating Aurora photos. They christened the previously unknown lighting phenomenon “Dune”. Because its even wave patterns resemble those in the sand of a dune.
But what is special about this new form of the Northern Lights? The researchers determined that the shimmering waves have a wavelength of around 45 kilometers and occur only at a height of around 100 kilometers. This is rather low for an aurora and is unusual for another reason: this region of the upper atmosphere is considered a rather restless area, which should make the formation of such smooth, regular layers of aurora impossible.
The fact that the “Dune” phenomenon still occurs in this region could be due to the inversion. Such temperature-related boundary layers sometimes form below the mesopause – only certain gravity waves can spread through them like in a channel. As the scientists suspect, the greenish glow of the new aurora is caused by oxygen atoms that are excited by the solar wind. Because the oxygen is compressed in a regular wave pattern by the gravity waves in the inversion zone, the Aurora forms its ripple pattern.
The Palmroth team now hopes to be able to collect more data on this phenomenon in the future. Only then can the origins of the “Dune” polar light be clearly clarified and further secrets of this lighting phenomenon revealed. Northern lights come in many different versions and there are some unusual shapes that still puzzle researchers: for example, flickering northern lights, pulsating aurors or the recently discovered “STEVE” phenomenon.