Citizen Scientists Discover a New Auroral Form: Dunes Provide Insight Into the Upper Atmosphere

Abstract

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...

Characteristics of fragmented aurora-like emissions (FAEs) observed on Svalbard

“…One such example is airglow, which can produce the same 557.7 nm and 630.0 nm emission lines of atomic oxygen as typical aurorae, but in this case it is due to dissociative electron recombination (e.g. Peverall et al, 2000). Interaction between aurorae and the dynamics of the neutral atmosphere is a complex subject, with features such as the recently discovered dunes potentially being caused by atmospheric wave modulation on diffuse aurorae (Palmroth et al, 2019).…”

“…Peverall et al, 2000). Interaction between aurorae and the dynamics of the neutral atmosphere is a complex subject, with features such as the recently discovered dunes potentially being caused by atmospheric wave modulation on diffuse aurorae (Palmroth et al, 2019). Thus, not all emissions similar to aurorae are caused by particle precipitation; Strong Thermal Emission Velocity Enhancement (STEVE) is already a well-known example of aurora-like skyglow which is likely caused by local acceleration processes instead of precipitation (Gallardo-Lacourt et al, 2018).…”

Lower-thermosphere–ionosphere (LTI) quantities: current status of measuring techniques and models

“…These simulations can be used to assess the electric and magnetic fields within large volumes and map them to the ionospheric plane. In fact, global MHD simulations have shown that the Poynting flux starts to focus towards the magnetosphere and ionosphere already from the solar wind in regions where the open field lines are dragged towards the tail (Papadopoulos et al, 1999;Palmroth et al, 2003;Palmroth et al, 2006c). Zhang et al (2012) used a global MHD simulation, mapped the Poynting flux in the tail to the ionosphere, and confirmed that its ionospheric distribution reproduced the global morphology of the Poynting flux measured by the Polar satellite.…”

Large‐Scale Dune Aurora Event Investigation Combining Citizen Scientists' Photographs and Spacecraft Observations

“…The horizontal phase speed of the dunes is also estimated based on the sole analysis of citizen scientist photographs, and it suggests an unusually large propagation speed which might reveal strong neutral winds at the dune altitude. The studied event took place on 20 January 2016 above Northern Europe; this event is part of the list given in the dune aurora seminal paper (Palmroth, Grandin, Helin, et al, 2020).…”