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 7 October 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 analyze 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. 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. Further, the dune project presents means to create general interest toward physics, emphasizing that citizens can take part in scientific work by helping to uncover new phenomena. Plain Language SummaryAbove Earth's atmosphere at about 80-120 km altitude, lies a region that is often dubbed as the "ignorosphere," one of the least explored regions at our planet. We present a new auroral form spotted by citizen scientists and show how it can be used to investigate the ignorosphere. We name the new form as "the dunes" and develop a method to analyze the citizen scientist pictures using the stars on the skies as reference points. The new method and other supporting data indicate that the dunes are a monochromatic wave field with a wavelength of about 45 km within a thin layer at 100 km altitude, right in the ignorosphere, where atmosphere meets the electromagnetic forcing from space. The analysis suggests that the dunes manifest atmospheric waves, possibly a rare phenomenon called mesospheric bores, which are large wave fields propagating in the ignorosphere. They have not previously been observed via aurora, nor at auroral latitudes and altitudes. The dunes present a new opportunity to investigate the ignorosphere and its driving from above. Further, the dune project presents means to create general interest toward physics, emphasizing that citizens can take part in scientific work by helping to uncover new phenomena. Key Points: • Citizen scientists discover a new auroral form, named the dunes, presenting a large-scale monochromatic wave field • We develop a triangulation method using citizen scientist photographs as science data • We suggest that the dunes manifest mesospheric bores, which have not previously been observed in the diffuse aurora Suppo...

<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>