Dune aurora: survey from a citizen science database

Abstract

Abstract. Auroral forms can provide information not only on the state of near-Earth space but also on conditions in the lower-thermosphere–ionosphere. The so-called dune aurora, consisting of brighter stripes forming a wave-like pattern in the dim, diffuse green aurora, has been hypothesised as being an optical signature revealing the presence of large-scale atmospheric waves above or near the mesopause. However, only a few dune aurora events have been studied to date, leaving many open questions regarding the nature of this phenomenon. We carry out the first systematic survey of dune aurora events by collecting citizen science observations of the dunes since 2000 using the Skywarden (https://taivaanvahti.fi, last access: 25 August 2026) database of observations. From a total of 308 dune aurora observations made during 61 different events by citizen scientists from Northern Europe, North America, Australia, and New Zealand, we investigate the distribution of dune events as a function of location, month, magnetic local time (MLT), solar wind and interplanetary magnetic field (IMF) conditions, and geomagnetic activity. We compare those distributions to that of all the aurora observations reported in Skywarden since 2000. We find that the vast majority (92 %) of the dune reports were made by observers below 61° geomagnetic latitude (to be compared to 74 % for all aurora observations), suggesting that they frequently occur in the equatorward part of the auroral oval. The dune observations are mostly (89 %) made in the pre-midnight sector, with a peak between 21:00 and 22:00 MLT (between 23:00 and 00:00 MLT for all aurora observations). The months with the highest number of reports of dune observations are October and March, which could be the result of a combination of geomagnetic, atmospheric, darkness, and cloudiness conditions needed for them to be observed. Regarding the solar wind and IMF driving parameters, no statistically significant differences are found between dune and all-aurora observations, but the differences are significant for geomagnetic indices, with dune observations being made during more active conditions than for all types of aurora considered together. Finally, we investigate a possible relationship between dune aurora and equivalent current patterns derived from ground-based magnetometer measurements. We find that, for all the reported events, the dunes are observed in association with strong (in most cases eastward but occasionally westward) auroral electrojet signatures and in the vicinity of the Harang discontinuity. These results suggest that the dune aurora formation mechanism might involve an interplay between proton precipitation, atmospheric dynamics, and nightside transition region processes.