Abstract
<p>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. Here, we present a new auroral form named "the dunes". On Oct 7, 2018, citizen observers took multiple digital photographs of the same dunes simultaneously from different locations in Finland and Sweden. We develop a triangulation method to analyse the photographs, and conclude that the dunes are a monochromatic wave field with a wavelength of about 45 km within a thin layer at 100 km altitude. Supporting data suggest that the dunes manifest atmospheric waves, possibly mesospheric bores, which are rarely detected, and have not previously been observed via diffuse aurora, nor at auroral latitudes and altitudes. The dunes present a new opportunity to investigate the coupling of the lower/middle atmosphere to the thermosphere and ionosphere. We conclude that the the dunes may provide new insights into the structure of the mesopause as a response to driving by ionospheric energy deposition via Joule heating and electron precipitation. Further, our paper adds to the growing body of work that illustrates the value of citizen scientist images in carrying out quantitative analysis of optical phenomena, especially at small scales at subauroral latitudes. The dune project presents means to create general interest towards physics, emphasising that citizens can take part in scientific work by helping to uncover new phenomena.</p>
Highlights
The auroral mesosphere-lower thermosphere-ionosphere (MLTI) region, often dubbed as the “ignorosphere” at about 65–80◦ in geographic latitude and at 80–120 km altitude is one of the most intriguing regions within the near-Earth space
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
We developed a novel method to analyze citizen scientist photographs with which we can place the dunes into a thin layer that has a constant altitude of 100 km
Summary
The auroral mesosphere-lower thermosphere-ionosphere (MLTI) region, often dubbed as the “ignorosphere” at about 65–80◦ in geographic latitude and at 80–120 km altitude is one of the most intriguing regions within the near-Earth space. Following a popular guidebook project to explain auroral forms to citizen observers (Palmroth et al, 2018), a group of Finnish auroral enthusiasts reported of several events with an unexplained auroral form presenting a monochromatic wave field in the auroral emission They named the waves as the dunes. Is located in the north, and there are finger-like rays of green emission extending equatorward from the bright arc These finger-like rays are called the dunes, pictured in Laitila in south-western Finland at 17:41 UT, where they were visible during 17:39–17:59 UT.
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