Eero Karvinen

Fragmented aurora-like emissions (fragments) are small-scale green E-region structures that have previously been reported mainly from high-latitude locations near the poleward auroral oval boundary. Here we present a global citizen-science dataset of 26 fragment observations from 2017 to 2025, collected through an international citizen-science campaign via the Skywarden platform. The observations span magnetic latitudes from approximately 53 to 76°, a wide range of magnetic local times and activity levels, both hemispheres, and diverse auroral conditions. The dataset substantially extends the observational record of fragments beyond previously reported high-latitude regions. Both isolated fragments (type I) and the quasi-periodic wave-like fragments (type II) are represented in this broader geographical context. To assess fragment locations relative to the auroral oval, three case studies combining satellite observations with ground-based auroral images were analysed in detail. These demonstrate that fragments occur poleward of the oval in Antarctica, equatorward of the oval in Manitoba, and within the oval near the diffuse-discrete boundary in Iceland. Together, the global dataset and case studies show that fragments occur across a much broader range of auroral and geomagnetic conditions and oval positions than previously documented. The results demonstrate the scientific value of citizen-science observations for studying short-lived and localised auroral phenomena.

Fragmented aurora-like emissions (fragments) are small-scale green E-region structures that have previously been reported mainly from high-latitude locations near the poleward auroral oval boundary. Here we present a global citizen-science dataset of 26 fragment observations from 2017 to 2025, collected through an international citizen-science campaign via the Skywarden platform. The observations span magnetic latitudes from approximately 53 to 76°, a wide range of magnetic local times and activity levels, both hemispheres, and diverse auroral conditions. The dataset substantially extends the observational record of fragments beyond previously reported high-latitude regions. Both isolated fragments (type I) and the quasi-periodic wave-like fragments (type II) are represented in this broader geographical context. To assess fragment locations relative to the auroral oval, three case studies combining satellite observations with ground-based auroral images were analysed in detail. These demonstrate that fragments occur poleward of the oval in Antarctica, equatorward of the oval in Manitoba, and within the oval near the diffuse-discrete boundary in Iceland. Together, the global dataset and case studies show that fragments occur across a much broader range of auroral and geomagnetic conditions and oval positions than previously documented. The results demonstrate the scientific value of citizen-science observations for studying short-lived and localised auroral phenomena.

Fragmented aurora-like emissions (fragments) are small-scale green E-region structures that have previously been reported mainly from high-latitude locations near the poleward auroral oval boundary. Here we present a global citizen-science dataset of 26 fragment observations from 2017 to 2025, collected through an international citizen-science campaign via the Skywarden platform. The observations span magnetic latitudes from approximately 53 to 76°, a wide range of magnetic local times and activity levels, both hemispheres, and diverse auroral conditions. The dataset substantially extends the observational record of fragments beyond previously reported high-latitude regions. Both isolated fragments (type I) and the quasi-periodic wave-like fragments (type II) are represented in this broader geographical context. To assess fragment locations relative to the auroral oval, three case studies combining satellite observations with ground-based auroral images were analysed in detail. These demonstrate that fragments occur poleward of the oval in Antarctica, equatorward of the oval in Manitoba, and within the oval near the diffuse-discrete boundary in Iceland. Together, the global dataset and case studies show that fragments occur across a much broader range of auroral and geomagnetic conditions and oval positions than previously documented. The results demonstrate the scientific value of citizen-science observations for studying short-lived and localised auroral phenomena.

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.

Fragmented aurora-like emissions (fragments) are small-scale green E-region structures that have previously been reported mainly from high-latitude locations near the poleward auroral oval boundary. Here we present a global citizen-science dataset of 26 fragment observations from 2017 to 2025, collected through an international citizen-science campaign via the Skywarden platform. The observations span magnetic latitudes from approximately 53 to 76°, a wide range of magnetic local times and activity levels, both hemispheres, and diverse auroral conditions. The dataset substantially extends the observational record of fragments beyond previously reported high-latitude regions. Both isolated fragments (type I) and the quasi-periodic wave-like fragments (type II) are represented in this broader geographical context. To assess fragment locations relative to the auroral oval, three case studies combining satellite observations with ground-based auroral images were analysed in detail. These demonstrate that fragments occur poleward of the oval in Antarctica, equatorward of the oval in Manitoba, and within the oval near the diffuse-discrete boundary in Iceland. Together, the global dataset and case studies show that fragments occur across a much broader range of auroral and geomagnetic conditions and oval positions than previously documented. The results demonstrate the scientific value of citizen-science observations for studying short-lived and localised auroral phenomena.

We investigate the origin of the continuum emissions observed in the poleward boundary dayside aurora discovered in Partamies et al. 2025, known as GHOST, and propose that they arise from highly excited, hot N₂. Using spectral modelling and fits to ground-based measurements of high-resolution GHOST spectra, we demonstrate that vibrationally and rotationally excited N₂ and N₂⁺ can reproduce the observed structured continuum without requiring emission from NO. Spectral fitting indicates that GHOST events coincide with extreme ion heating and high neutral temperatures. Background conditions from additional events indicate that strong ionospheric flows are typically present, which can help to provide the necessary energy input for producing hot neutral and ionised N₂. Proton aurora observations and EISCAT incoherent scatter radar measurements of ionospheric plasma parameters indicate that two of our three events are located in the cusp. These results suggest that the combination of strong flow, heating, particle precipitation, and cusp conditions produce thermally excited N₂ populations which can account for the continuum spectrum of GHOST.

We investigate the origin of the continuum emissions observed in the poleward boundary dayside aurora discovered in Partamies et al. 2025, known as GHOST, and propose that they arise from highly excited, hot N₂. Using spectral modelling and fits to ground-based measurements of high-resolution GHOST spectra, we demonstrate that vibrationally and rotationally excited N₂ and N₂⁺ can reproduce the observed structured continuum without requiring emission from NO. Spectral fitting indicates that GHOST events coincide with extreme ion heating and high neutral temperatures. Background conditions from additional events indicate that strong ionospheric flows are typically present, which can help to provide the necessary energy input for producing hot neutral and ionised N₂. Proton aurora observations and EISCAT incoherent scatter radar measurements of ionospheric plasma parameters indicate that two of our three events are located in the cusp. These results suggest that the combination of strong flow, heating, particle precipitation, and cusp conditions produce thermally excited N₂ populations which can account for the continuum spectrum of GHOST.

Fragmented aurora-like emissions (fragments) are small-scale green E-region structures that have previously been reported mainly from high-latitude locations near the poleward auroral oval boundary. Here we present a global citizen-science dataset of 26 fragment observations from 2017 to 2025, collected through an international citizen-science campaign via the Skywarden platform. The observations span magnetic latitudes from approximately 53 to 76°, a wide range of magnetic local times and activity levels, both hemispheres, and diverse auroral conditions. The dataset substantially extends the observational record of fragments beyond previously reported high-latitude regions. Both isolated fragments (type I) and the quasi-periodic wave-like fragments (type II) are represented in this broader geographical context. To assess fragment locations relative to the auroral oval, three case studies combining satellite observations with ground-based auroral images were analysed in detail. These demonstrate that fragments occur poleward of the oval in Antarctica, equatorward of the oval in Manitoba, and within the oval near the diffuse-discrete boundary in Iceland. Together, the global dataset and case studies show that fragments occur across a much broader range of auroral and geomagnetic conditions and oval positions than previously documented. The results demonstrate the scientific value of citizen-science observations for studying short-lived and localised auroral phenomena.

We investigate the origin of the continuum emissions observed in the poleward boundary dayside aurora discovered in Partamies et al. 2025, known as GHOST, and propose that they arise from highly excited, hot N₂. Using spectral modelling and fits to ground-based measurements of high-resolution GHOST spectra, we demonstrate that vibrationally and rotationally excited N₂ and N₂⁺ can reproduce the observed structured continuum without requiring emission from NO. Spectral fitting indicates that GHOST events coincide with extreme ion heating and high neutral temperatures. Background conditions from additional events indicate that strong ionospheric flows are typically present, which can help to provide the necessary energy input for producing hot neutral and ionised N₂. Proton aurora observations and EISCAT incoherent scatter radar measurements of ionospheric plasma parameters indicate that two of our three events are located in the cusp. These results suggest that the combination of strong flow, heating, particle precipitation, and cusp conditions produce thermally excited N₂ populations which can account for the continuum spectrum of GHOST.

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 statistical analysis of dune aurora events by collecting citizen science observations of the dunes since 2000 using the Skywarden (https://taivaanvahti.fi) database of observations. From a total of 289 dune aurora observations made during 56 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, local time, 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 also estimate the duration of dune events based on the available observations, and we investigate a possible relationship between dune aurora and equivalent current patterns derived from ground-based magnetometer measurements. We find that the vast majority of dune observations take place near the equatorward boundary of the auroral oval, in the dusk sector earlier than the peak in all auroral report distribution, and in association with strong (in most cases eastward but occasionally westward) auroral electrojet signatures. The dune observations are often associated with elevated solar wind density and IMF magnitude, and the IMF B_y component may play a role in their formation. Finally, their monthly distribution peaks in March and October, which could be the result of a combination of geomagnetic, atmospheric, darkness, and cloudiness conditions needed for them to form.