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

• Published in: AGU advances Vol. 2; no. 2
• Main Authors: Grandin, Maxime, Palmroth, Minna, Whipps, Graeme, Kalliokoski, Milla, Ferrier, Mark, Paxton, Larry J., Mlynczak, Martin G., Hilska, Jukka, Holmseth, Knut, Vinorum, Kjetil, Whenman, Barry
• Format: Journal Article
• Language: English
• Published: Hoboken John Wiley & Sons, Inc 01.06.2021; Wiley
• Subjects: Altitude; Atmosphere; Cameras; citizen science; dune aurora; Dunes; Hypotheses; Investigations; ionosphere‐atmosphere interactions; mesospheric bore; Propagation; Satellites; Scientists; Spacecraft; Norway; Scotland; Finland; United Kingdom > UK
• ISSN: 2576-604X; 2576-604X
• DOI: 10.1029/2020AV000338

Recently, citizen scientist photographs led to the discovery of a new auroral form called “the dune aurora” which exhibits parallel stripes of brighter emission in the green diffuse aurora at about 100 km altitude. This discovery raised several questions, such as (i) whether the dunes are associated with particle precipitation, (ii) whether their structure arises from spatial inhomogeneities in the precipitating fluxes or in the underlying neutral atmosphere, and (iii) whether they are the auroral manifestation of an atmospheric wave called a mesospheric bore. This study investigates a large‐scale dune aurora event on 20 January 2016 above Northern Europe. The dunes were observed from Finland to Scotland, spanning over 1,500 km for at least 4 h. Spacecraft observations indicate that the dunes are associated with particle precipitation and reveal the presence of a temperature inversion layer below the mesopause during the event, creating suitable conditions for mesospheric bore formation. The analysis of a time lapse of pictures by a citizen scientist from Scotland leads to the estimate that, during this event, the dunes propagate toward the west‐southwest direction at about 200 m s−1, presumably indicating strong horizontal winds near the mesopause. These results show that citizen science and dune aurora studies can fill observational gaps and be powerful tools to investigate the least‐known region of near‐Earth space at altitudes near 100 km. Plain Language Summary Citizen science recently led to the discovery of a new form of aurora called “the dunes,” which consists of a modulation of the brightness in the green diffuse aurora, forming regularly spaced, parallel stripes of brighter emission. This study investigates the nature of the dune aurora by combining photographs taken by citizen scientists and satellite observations during a large‐scale event which took place above Northern Europe on 20 January 2016. The dunes were observed from Finland to Scotland, spanning over 1,500 km for at least 4 h. Observations from satellites indicate that the dunes are associated with the precipitation of particles from near‐Earth space into the upper atmosphere, and that the atmospheric temperature profile within 60–110 km altitude exhibits features which allow the formation of an atmospheric wave type called “mesospheric bore,” which has been suggested as a possible explanation for the dunes' morphology. Finally, the dune propagation speed is estimated for the first time using a timelapse of pictures by a Scottish citizen scientist and suggests the presence of strong horizontal winds in the upper atmosphere. Key Points During a dune aurora event spanning over 1,500 km, satellite observations indicate that auroral precipitation takes place in the dune area The presence of a mesospheric temperature inversion layer near the dunes provides suitable conditions for mesospheric bore propagation The dune propagation speed is estimated for the first time and suggests that strong horizontal winds were present during the event