Articles | Volume 44, issue 1
https://doi.org/10.5194/angeo-44-63-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-44-63-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Regular paper
| 
03 Feb 2026
Regular paper |
| 03 Feb 2026
| 03 Feb 2026
Observations of fragmented aurora-like emissions and picket fence on the poleward edge of the auroral oval
Swedish Institute of Space Physics (IRF), Kiruna, Sweden
Katie Herlingshaw
University Centre in Svalbard, Longyearbyen, Norway
Tima Sergienko
Swedish Institute of Space Physics (IRF), Kiruna, Sweden
Gaël Cessateur
Royal Belgian Institute for Space Aeronomy, Brussels, Belgium
Noora Partamies
University Centre in Svalbard, Longyearbyen, Norway
Magnar G. Johnsen
Tromsø Geophysical Observatory, UiT The Arctic University of Norway, Tromsø, Norway
Keisuke Hosokawa
Graduate School of Informatics and Engineering, The University of Electro-Communications, Chofu, Japan
Hervé Lamy
Royal Belgian Institute for Space Aeronomy, Brussels, Belgium
Yasunobu Ogawa
National Institute of Polar Research, Tachikawa, Japan
Antti Kero
Sodankylä Geophysical Observatory, Sodankylä, Finland
Shin-ichiro Oyama
National Institute of Polar Research, Tachikawa, Japan
Nagoya University, Nagoya, Japan
University of Oulu, Oulu, Finland
Masatoshi Yamauchi
Swedish Institute of Space Physics (IRF), Kiruna, Sweden
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Gaël Cessateur, Christian Buil, Guillaume Bertrand, Matthieu Le Lain, Valérie Desnoux, Olivier Garde, Hervé Lamy, Mathieu Barthelemy, Magnar Gullikstad Johnsen, David Bolsée, Urban Brändström, Antoine Calegaro, Fabien Darrouzet, Rowan Dayton-Oxland, Johan De Keyser, Maxime Grandin, Kirsti Kauristie, Romain Maggiolo, Sota Nanjo, and Noora Partamies
EGUsphere, https://doi.org/10.5194/egusphere-2026-5461, https://doi.org/10.5194/egusphere-2026-5461, 2026
This preprint is open for discussion and under review for Geoscientific Instrumentation, Methods and Data Systems (GI).
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We developed a compact, portable instrument that records the colours of auroras across a broad range of visible and near-infrared light. Field tests in northern Norway showed that it can capture several important auroral emissions at the same time and can be operated with simple portable equipment. This makes it suitable for coordinated observations from multiple sites, helping researchers study how auroras vary in space and time.
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EGUsphere, https://doi.org/10.5194/egusphere-2026-5693, https://doi.org/10.5194/egusphere-2026-5693, 2026
This preprint is open for discussion and under review for Annales Geophysicae (ANGEO).
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Auroral colors are used to estimate the energy of particles entering Earth's atmosphere, but the processes producing those colors are not always well known. Using five cameras in northern Sweden and two computer models, we measured where two auroral emissions were produced. We found that a process involving oxygen molecules shifts one emission to lower altitudes and improves agreement between models and observations by about 70%. This can make estimates of auroral particle energy more reliable.
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Ann. Geophys., 44, 1023–1042, https://doi.org/10.5194/angeo-44-1023-2026, https://doi.org/10.5194/angeo-44-1023-2026, 2026
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Pulsating aurora often contains rapid brightness changes, but their overall behavior has not been well measured. We analyzed high-speed camera images from northern Sweden and Norway with machine learning to identify when these rapid changes occur. We found that they become more common toward the morning and at the lower-latitude sector. This suggests that small-scale auroral fluctuation can help reveal how particles from near-Earth space enter the upper atmosphere.
Vanina Lanabere, Stephan Buchert, Adrian Blagau, Harriet George, Sota Nanjo, Liisa Juusola, Andrew P. Dimmock, Samuel Wharton, Heikki Vanhamäki, Octav Marghitu, Louis Richard, Lei Cai, Alice V. L. Wallner, Daria Kotova, Yaqi Jin, Theresa Hoppe, Jennifer A. Carter, and Anita Aikio
Ann. Geophys., 44, 977–1001, https://doi.org/10.5194/angeo-44-977-2026, https://doi.org/10.5194/angeo-44-977-2026, 2026
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We studied a series of fast plasma streams that connected Earth’s nightside magnetic environment with the high‑latitude ionized upper atmosphere on 7 December 2023. Using satellite, auroral images and ground observations, we showed how each stream disturbed the upper atmosphere. Their repeated impact strengthened these disturbances until a substorm began, revealing how small events can build up to a larger magnetic disruption.
Sota Nanjo, Satoshi Kurita, Tima Sergienko, Yoshizumi Miyoshi, and Ryuho Kataoka
Ann. Geophys., 44, 959–975, https://doi.org/10.5194/angeo-44-959-2026, https://doi.org/10.5194/angeo-44-959-2026, 2026
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Using a high-speed camera with a wide view of the sky, we observed rapidly blinking aurora across several hundred kilometers. We found that different parts of the same auroral arc can blink at different rhythms at the same time, and that these rhythms move together with the arc. Although larger bright patches sometimes blink more slowly, this pattern does not hold overall. These results improve our understanding of how invisible space processes shape the visible northern lights.
Tomoe Taki, Tima Sergienko, Urban Brändström, Yasunobu Ogawa, Sota Nanjo, and Juan Araújo
EGUsphere, https://doi.org/10.5194/egusphere-2026-1133, https://doi.org/10.5194/egusphere-2026-1133, 2026
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This study explored electric forces near a auroral arc during a rocket experiment in northern Sweden. A rocket released glowing clouds high above Earth, and we tracked their motion as an aurora passed through them. By reconstructing their motion in three dimensions, we estimated the magnitude and direction of the surrounding electric field. We found that the field changed direction and became weaker near the arc, revealing the structure of electric currents correspond to auroral activity.
Gaël Cessateur, Keisuke Hosokawa, Hervé Lamy, Sota Nanjo, Mathieu Barthelemy, Magnar G. Johnsen, and Romain Maggiolo
EGUsphere, https://doi.org/10.5194/egusphere-2026-385, https://doi.org/10.5194/egusphere-2026-385, 2026
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The Auroral Spectrograph in Skibotn has been measuring auroral light spectra since October 2023. We estimate the energy of electrons producing diffuse auroras from red oxygen and blue nitrogen emissions. Our statistical analysis shows that electron energy increases toward the morning sector, confirming previous studies: electron scattering by chorus waves can populate the loss cone and lead to precipitation, while changes in resonance conditions toward dawn favor harder electrons
Sota Nanjo, Masatoshi Yamauchi, Magnar Gullikstad Johnsen, Yoshihiro Yokoyama, Urban Brändström, Yasunobu Ogawa, Anna Naemi Willer, and Keisuke Hosokawa
Ann. Geophys., 43, 303–317, https://doi.org/10.5194/angeo-43-303-2025, https://doi.org/10.5194/angeo-43-303-2025, 2025
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Our research explores the shock aurora, which is typically observed on the dayside due to the rapid compression of the Earth's magnetic field. We observed this rare aurora on the nightside, a region where such events are difficult to detect. Using ground-based cameras, we identified new features, including leaping and vortex-like patterns. These findings offer a fresh insight into the interactions between the solar wind and the magnetosphere, enhancing our understanding of space weather and its effects.
Sota Nanjo, Tomoe Taki, Tima Sergienko, and Urban Brändström
EGUsphere, https://doi.org/10.5194/egusphere-2026-5693, https://doi.org/10.5194/egusphere-2026-5693, 2026
This preprint is open for discussion and under review for Annales Geophysicae (ANGEO).
Short summary
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Auroral colors are used to estimate the energy of particles entering Earth's atmosphere, but the processes producing those colors are not always well known. Using five cameras in northern Sweden and two computer models, we measured where two auroral emissions were produced. We found that a process involving oxygen molecules shifts one emission to lower altitudes and improves agreement between models and observations by about 70%. This can make estimates of auroral particle energy more reliable.
Gaël Cessateur, Christian Buil, Guillaume Bertrand, Matthieu Le Lain, Valérie Desnoux, Olivier Garde, Hervé Lamy, Mathieu Barthelemy, Magnar Gullikstad Johnsen, David Bolsée, Urban Brändström, Antoine Calegaro, Fabien Darrouzet, Rowan Dayton-Oxland, Johan De Keyser, Maxime Grandin, Kirsti Kauristie, Romain Maggiolo, Sota Nanjo, and Noora Partamies
EGUsphere, https://doi.org/10.5194/egusphere-2026-5461, https://doi.org/10.5194/egusphere-2026-5461, 2026
This preprint is open for discussion and under review for Geoscientific Instrumentation, Methods and Data Systems (GI).
Short summary
Short summary
We developed a compact, portable instrument that records the colours of auroras across a broad range of visible and near-infrared light. Field tests in northern Norway showed that it can capture several important auroral emissions at the same time and can be operated with simple portable equipment. This makes it suitable for coordinated observations from multiple sites, helping researchers study how auroras vary in space and time.
Sota Nanjo, Tomoe Taki, Keisuke Hosokawa, Urban Brändström, Yoshizumi Miyoshi, and Magnar G. Johnsen
Ann. Geophys., 44, 1023–1042, https://doi.org/10.5194/angeo-44-1023-2026, https://doi.org/10.5194/angeo-44-1023-2026, 2026
Short summary
Short summary
Pulsating aurora often contains rapid brightness changes, but their overall behavior has not been well measured. We analyzed high-speed camera images from northern Sweden and Norway with machine learning to identify when these rapid changes occur. We found that they become more common toward the morning and at the lower-latitude sector. This suggests that small-scale auroral fluctuation can help reveal how particles from near-Earth space enter the upper atmosphere.
Jia Jia, Yvan Orsolini, Monika E. Szeląg, Antti Kero, Pekka T. Verronen, Maxime Grandin, Patrick J. Espy, Sebastian Käki, Neethal Thomas, Max van de Kamp, Sergey Koldobskiy, Jiarong Zhang, and Noora Partamies
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Geomagnetic storms connect space weather to Earth's atmosphere. Analysing four major Solar Cycle 25 storms, we show that energetic particles cause mesospheric ozone losses of up to 80 %, with distinct responses to energetic electron precipitation and solar proton events. Combining observations and simulations reveals shortcomings in current representations of upper-atmospheric coupling and points to the need for sustained measurements of energetic particles and atmospheric composition.
Vanina Lanabere, Stephan Buchert, Adrian Blagau, Harriet George, Sota Nanjo, Liisa Juusola, Andrew P. Dimmock, Samuel Wharton, Heikki Vanhamäki, Octav Marghitu, Louis Richard, Lei Cai, Alice V. L. Wallner, Daria Kotova, Yaqi Jin, Theresa Hoppe, Jennifer A. Carter, and Anita Aikio
Ann. Geophys., 44, 977–1001, https://doi.org/10.5194/angeo-44-977-2026, https://doi.org/10.5194/angeo-44-977-2026, 2026
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We studied a series of fast plasma streams that connected Earth’s nightside magnetic environment with the high‑latitude ionized upper atmosphere on 7 December 2023. Using satellite, auroral images and ground observations, we showed how each stream disturbed the upper atmosphere. Their repeated impact strengthened these disturbances until a substorm began, revealing how small events can build up to a larger magnetic disruption.
Sota Nanjo, Satoshi Kurita, Tima Sergienko, Yoshizumi Miyoshi, and Ryuho Kataoka
Ann. Geophys., 44, 959–975, https://doi.org/10.5194/angeo-44-959-2026, https://doi.org/10.5194/angeo-44-959-2026, 2026
Short summary
Short summary
Using a high-speed camera with a wide view of the sky, we observed rapidly blinking aurora across several hundred kilometers. We found that different parts of the same auroral arc can blink at different rhythms at the same time, and that these rhythms move together with the arc. Although larger bright patches sometimes blink more slowly, this pattern does not hold overall. These results improve our understanding of how invisible space processes shape the visible northern lights.
Marie Vigger Eldor, Magnar Gullikstad Johnsen, Nils Olsen, and Anna Naemi Willer
Ann. Geophys., 44, 811–823, https://doi.org/10.5194/angeo-44-811-2026, https://doi.org/10.5194/angeo-44-811-2026, 2026
Short summary
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Rapid geomagnetic variations in the ultra-low frequency band are observed using ground-based magnetometers. We apply four years of data from West Greenland in a statistical analysis of the distribution of such variations. We identify a rapid geomagnetic variation population associated with the magnetospheric cusp that is separate from the auroral oval during summer. Earlier studies, which were mainly performed in winter, failed to unambiguously identify these variations.
Gaël Cessateur, Jean Lilensten, Hervé Lamy, Léo Bosse, Magnar G. Johnsen, Antonio Guerrero, David Bolsée, Mathieu Barthelemy, Thijs A. Stockmans, and Frans Snik
EGUsphere, https://doi.org/10.5194/egusphere-2026-3324, https://doi.org/10.5194/egusphere-2026-3324, 2026
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Auroras are more than beautiful lights: the way their light is polarized may reveal how charged particles enter the upper atmosphere. Such measurements have so far been limited to instruments that observe only a very small part of the sky. In this study, we show that a new polarization camera can map this signal across an aurora. We find that the polarization angle often changes coherently across the scene, while the polarization strength decreases in the brightest parts.
Charlotte M. van Hazendonk, Lisa J. Baddeley, Karl M. Laundal, and Noora Partamies
Ann. Geophys., 44, 697–714, https://doi.org/10.5194/angeo-44-697-2026, https://doi.org/10.5194/angeo-44-697-2026, 2026
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This study shows the first observations of the upflow of ions in the Earth's ionosphere generated by ultra-low frequency waves. These waves are visible as auroral arcs. Using various instruments and models, their complex dynamics and the coupling between the ionosphere and magnetosphere were highlighted. Results show significant energy dissipation and currents, even from small-scale waves, highlighting the importance of a multi-instrument approach to understanding such phenomena.
Lena Mielke, Katie Herlingshaw, Noora Partamies, Maxime Grandin, Emma Bruus, Rowan Dayton-Oxland, Donna Lach, Marjan Spijkers, Vincent Ledvina, Eero Karvinen, Andres Spicher, Benjamin Eberhardt, and Olivier Staiger
EGUsphere, https://doi.org/10.5194/egusphere-2026-3756, https://doi.org/10.5194/egusphere-2026-3756, 2026
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This study presents 26 citizen science observations of fragmented aurora-like emissions, here called fragments, from around the world. Using auroral images and satellite and solar wind data, we found that these short-lived fragments appear across a wide range of magnetic latitudes and local times. They can occur not only poleward of the auroral oval, but also within and equatorward of it. These findings broaden where fragments are known to occur and highlight the value of citizen science.
Thomas B. Leyser, Tima Sergienko, Yoshihiro Yokoyama, Tomoe Taki, and Urban Brändström
EGUsphere, https://doi.org/10.5194/egusphere-2026-2925, https://doi.org/10.5194/egusphere-2026-2925, 2026
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The BROR rocket experiment, launched from Esrange near Kiruna, Sweden, involved releases of barium clouds in the thermosphere to study auroral structures. The barium was ejected by the explosion-like combustion of ignited thermite. Shock waves could be observed to follow the ejections when the rocket speed was supersonic, but not when subsonic. The shock waves are attributed to ejected particulate matter from the thermite combustion that traveled at supersonic speed.
Biagio Forte, Andrzej Krankowski, Kacper Kotulak, Derek McKay, Ingemar Häggström, John S. Morgan, Richard A. Fallows, Mario M. Bisi, Paul Kinsler, Leszek Błaszkiewicz, Tianchu Lu, Antti Kero, Paweł Flisek, Adam Fron, Michal Kownacki, Bartosz Radzanowski, and Katarzyna Beser
EGUsphere, https://doi.org/10.5194/egusphere-2026-1741, https://doi.org/10.5194/egusphere-2026-1741, 2026
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This work illustrates a novel ionospheric experiment combining different instruments. Modern radio telescopes have a higher sensitivity than traditional ionospheric instruments (e.g., satellite radio receivers, incoherent scatter radars). This experiment demonstrates how the combination of evidence from modern and traditional instruments allows the characterisation of ionospheric structures over multiple spatial scales: a significant advancement from the capabilities of traditional instruments.
Masatoshi Yamauchi, Yoshihiro Yokoyama, Tsubasa Kotani, and Jürgen Matzka
EGUsphere, https://doi.org/10.5194/egusphere-2026-1517, https://doi.org/10.5194/egusphere-2026-1517, 2026
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The interplanetary shock such as the coronal mass ejections (CME) generally propagates faster than the solar wind, and predicting the propagation speed and the arrival time of hazardous CMEs are important for the space weather prediction. However, it is still difficult to model correctly. This paper statistically study the relation between the solar wind speed and the shock propagation speed.
Liisa Juusola, Ari Viljanen, Ilja Honkonen, Magnar Gullikstad Johnsen, Andrew Dimmock, Vanina Lanabere, and Alice Wallner
EGUsphere, https://doi.org/10.5194/egusphere-2026-1110, https://doi.org/10.5194/egusphere-2026-1110, 2026
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During severe space storms, the induced geoelectric field has the potential to cause substantial problems in power grids. We examine the geomagnetically induced currents (GIC) the geoelectric field would have driven in a simple model power grid located in Northern Europe during the May 2024 superstorm. Our results help us understand how the complicated interaction between the driving from space and the response of the conducting ground produces the most intense GIC peaks.
Tomoe Taki, Tima Sergienko, Urban Brändström, Yasunobu Ogawa, Sota Nanjo, and Juan Araújo
EGUsphere, https://doi.org/10.5194/egusphere-2026-1133, https://doi.org/10.5194/egusphere-2026-1133, 2026
Short summary
Short summary
This study explored electric forces near a auroral arc during a rocket experiment in northern Sweden. A rocket released glowing clouds high above Earth, and we tracked their motion as an aurora passed through them. By reconstructing their motion in three dimensions, we estimated the magnitude and direction of the surrounding electric field. We found that the field changed direction and became weaker near the arc, revealing the structure of electric currents correspond to auroral activity.
Kian Sartipzadeh, Andreas Kvammen, Björn Gustavsson, Njål Gulbrandsen, Magnar G. Johnsen, Devin Huyghebaert, and Juha Vierinen
Ann. Geophys., 44, 85–107, https://doi.org/10.5194/angeo-44-85-2026, https://doi.org/10.5194/angeo-44-85-2026, 2026
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Knowledge of the charged environment in the upper atmosphere is essential for understanding space weather effects on satellites and radio communication. This environment is difficult to estimate at high latitudes, where aurora cause strong variability. We developed an artificial intelligence model to estimate this environment continuously. Our results show that the model provides reliable estimates even during auroral activity, improving monitoring of the polar upper atmosphere.
Gaël Cessateur, Keisuke Hosokawa, Hervé Lamy, Sota Nanjo, Mathieu Barthelemy, Magnar G. Johnsen, and Romain Maggiolo
EGUsphere, https://doi.org/10.5194/egusphere-2026-385, https://doi.org/10.5194/egusphere-2026-385, 2026
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The Auroral Spectrograph in Skibotn has been measuring auroral light spectra since October 2023. We estimate the energy of electrons producing diffuse auroras from red oxygen and blue nitrogen emissions. Our statistical analysis shows that electron energy increases toward the morning sector, confirming previous studies: electron scattering by chorus waves can populate the loss cone and lead to precipitation, while changes in resonance conditions toward dawn favor harder electrons
Stephen Omondi, Spencer Mark Hatch, Andreas Kvammen, Magnar Gullikstad Johnsen, Mathew J. Owens, Kristian Solheim Thinn, and Rodrigo López
EGUsphere, https://doi.org/10.5194/egusphere-2025-6298, https://doi.org/10.5194/egusphere-2025-6298, 2026
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Researchers tested whether combining real-time solar wind data with forecasts can improve predictions of local geomagnetic activity in Norway. Using a machine learning model, they found that accurate solar wind speed and magnetic field direction are key for reliable forecasts over 3 hours ahead, while CME arrival time only helps if magnetic field data is precise.
Rowan Dayton-Oxland, Fiona Ball, Daniel Whiter, Srimoyee Samaddar, Noora Partamies, Mathieu Barthelemy, Katie Herlingshaw, and Eero Karvinen
EGUsphere, https://doi.org/10.5194/egusphere-2025-5317, https://doi.org/10.5194/egusphere-2025-5317, 2025
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GHOST is a pale mauve aurora, usually seen near noon in Svalbard during polar night, emitting a continuum spectrum across the visible range. Our fitting of high-resolution spectra shows that GHOST emission is best explained by extremely hot nitrogen and oxygen molecules, not by the more scarce nitrous oxide which is usually assumed. We propose that strong ionospheric flows, daylight, and incoming solar‑wind particles combine to heat the upper atmosphere, priming it to produce GHOST aurora.
Liisa Juusola, Ilkka Virtanen, Spencer Mark Hatch, Heikki Vanhamäki, Maxime Grandin, Noora Partamies, Urs Ganse, Ilja Honkonen, Abiyot Workayehu, Antti Kero, and Minna Palmroth
Ann. Geophys., 43, 755–781, https://doi.org/10.5194/angeo-43-755-2025, https://doi.org/10.5194/angeo-43-755-2025, 2025
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Key properties of the ionospheric electrodynamics are electric fields, currents, and conductances. They provide a window to the vast and distant near-Earth space, cause Joule heating that affect satellite orbits, and drive geomagnetically induced currents (GICs) in technological conductor networks. We have developed a new method for solving the key properties of ionospheric electrodynamics from ground-based magnetic field observations.
Ilkka I. Virtanen, Ayanew Nigusie, Antti Kero, Neethal Thomas, and Juhana Lankinen
Atmos. Meas. Tech., 18, 5895–5917, https://doi.org/10.5194/amt-18-5895-2025, https://doi.org/10.5194/amt-18-5895-2025, 2025
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EISCAT3D is an ionospheric radar currently under construction in Northern Fenno-Scandinavia. The radar will make 3D measurements of the ionosphere at 50–1000 km altitudes. We show that the so-called multipurpose radar modulations and optimal data analysis can improve the time resolution of the measurements by more than an order of magnitude, and they enable one to measure ion-neutral collision frequencies, which are proportional to neutral particle density, in the lower ionosphere.
Tomotaka M. Tanaka, Yasunobu Ogawa, Yuto Katoh, Mizuki Fukizawa, Anton Artemyev, Vassilis Angelopoulos, Xiao-Jia Zhang, Yoshimasa Tanaka, and Akira Kadokura
Ann. Geophys., 43, 621–631, https://doi.org/10.5194/angeo-43-621-2025, https://doi.org/10.5194/angeo-43-621-2025, 2025
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The magnetic mirror force bends the orbits of electrons precipitating into the atmosphere. It has been suggested that relativistic electrons make much less ionization due to the force than if it did not exist, but the actual effectivity in the atmospheric electron density has not been revealed. We used conjugated observational data from the ELFIN (Electron Losses and Fields INvestigation) satellite and the EISCAT (European Incoherent SCATter scientific radar system) Tromsø radar to find that the electron density decreased by about 40 % at 80 km altitude because of the force.
Pekka T. Verronen, Akira Mizuno, Yoshizumi Miyoshi, Sandeep Kumar, Taku Nakajima, Shin-Ichiro Oyama, Tomoo Nagahama, Satonori Nozawa, Monika E. Szeląg, Tuomas Häkkilä, Niilo Kalakoski, Antti Kero, Esa Turunen, Satoshi Kasahara, Shoichiro Yokota, Kunihiro Keika, Tomoaki Hori, Takefumi Mitani, Takeshi Takashima, and Iku Shinohara
Ann. Geophys., 43, 561–578, https://doi.org/10.5194/angeo-43-561-2025, https://doi.org/10.5194/angeo-43-561-2025, 2025
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We use NO column density data from the Syowa station in Antarctica from 2012–2017. We compare these ground-based radiometer observations with results from a global atmosphere model to understand the year-to-year and day-to-day variability, shortcomings of current electron forcing, and how geomagnetic storms are driving the variability of NO. Our results demonstrate an underestimation in the magnitude of day-to-day variability in simulations, which calls for improved electron forcing in models.
Noora Partamies, Rowan Dayton-Oxland, Katie Herlingshaw, Ilkka Virtanen, Bea Gallardo-Lacourt, Mikko Syrjäsuo, Fred Sigernes, Takanori Nishiyama, Toshi Nishimura, Mathieu Barthelemy, Anasuya Aruliah, Daniel Whiter, Lena Mielke, Maxime Grandin, Eero Karvinen, Marjan Spijkers, and Vincent E. Ledvina
Ann. Geophys., 43, 349–367, https://doi.org/10.5194/angeo-43-349-2025, https://doi.org/10.5194/angeo-43-349-2025, 2025
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We studied the first broad band emissions, called continuum, in the dayside aurora. They are similar to Strong Thermal Emission Velocity Enhancement (STEVE) with white-, pale-pink-, or mauve-coloured light. But unlike STEVE, they follow the dayside aurora forming rays and other dynamic shapes. We used ground optical and radar observations and found evidence of heating and upwelling of both plasma and neutral air. This study provides new information on conditions for continuum emission, but its understanding will require further work.
Sota Nanjo, Masatoshi Yamauchi, Magnar Gullikstad Johnsen, Yoshihiro Yokoyama, Urban Brändström, Yasunobu Ogawa, Anna Naemi Willer, and Keisuke Hosokawa
Ann. Geophys., 43, 303–317, https://doi.org/10.5194/angeo-43-303-2025, https://doi.org/10.5194/angeo-43-303-2025, 2025
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Our research explores the shock aurora, which is typically observed on the dayside due to the rapid compression of the Earth's magnetic field. We observed this rare aurora on the nightside, a region where such events are difficult to detect. Using ground-based cameras, we identified new features, including leaping and vortex-like patterns. These findings offer a fresh insight into the interactions between the solar wind and the magnetosphere, enhancing our understanding of space weather and its effects.
Ingeborg Frøystein and Magnar Gullikstad Johnsen
Ann. Geophys., 43, 241–269, https://doi.org/10.5194/angeo-43-241-2025, https://doi.org/10.5194/angeo-43-241-2025, 2025
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The complete time series of the geomagnetic disturbance index (K) from Norwegian magnetic observatories have been digitized. We compare and discuss the tree methods used to derive the index, finding that each method has strengths and weaknesses. In total, we present all K indices derived from Norwegian observatories since the 1930s until today, the used derivation methods and the long historic time series as a whole, enabling critical use for future scientific work.
Maxime Grandin, Emma Bruus, Vincent E. Ledvina, Noora Partamies, Mathieu Barthelemy, Carlos Martinis, Rowan Dayton-Oxland, Bea Gallardo-Lacourt, Yukitoshi Nishimura, Katie Herlingshaw, Neethal Thomas, Eero Karvinen, Donna Lach, Marjan Spijkers, and Calle Bergstrand
Geosci. Commun., 7, 297–316, https://doi.org/10.5194/gc-7-297-2024, https://doi.org/10.5194/gc-7-297-2024, 2024
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We carried out a citizen science study of aurora sightings and technological disruptions experienced during the extreme geomagnetic storm of 10 May 2024. We collected reports from 696 observers from over 30 countries via an online survey, supplemented with observations logged in the Skywarden database. We found that the aurora was seen from exceptionally low latitudes and had very bright red and pink hues, suggesting that high fluxes of low-energy electrons from space entered the atmosphere.
Tinna L. Gunnarsdottir, Ingrid Mann, Wuhu Feng, Devin R. Huyghebaert, Ingemar Haeggstroem, Yasunobu Ogawa, Norihito Saito, Satonori Nozawa, and Takuya D. Kawahara
Ann. Geophys., 42, 213–228, https://doi.org/10.5194/angeo-42-213-2024, https://doi.org/10.5194/angeo-42-213-2024, 2024
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Several tons of meteoric particles burn up in our atmosphere each day. This deposits a great deal of material that binds with other atmospheric particles and forms so-called meteoric smoke particles. These particles are assumed to influence radar measurements. Here, we have compared radar measurements with simulations of a radar spectrum with and without dust particles and found that dust influences the radar spectrum in the altitude range of 75–85 km.
Yoshimasa Tanaka, Yasunobu Ogawa, Akira Kadokura, Takehiko Aso, Björn Gustavsson, Urban Brändström, Tima Sergienko, Genta Ueno, and Satoko Saita
Ann. Geophys., 42, 179–190, https://doi.org/10.5194/angeo-42-179-2024, https://doi.org/10.5194/angeo-42-179-2024, 2024
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We present via simulation how useful monochromatic images taken by a multi-point imager network are for auroral research in the EISCAT_3D project. We apply the generalized-aurora computed tomography (G-ACT) to modeled multiple auroral images and ionospheric electron density data. It is demonstrated that G-ACT provides better reconstruction results than the normal ACT and can interpolate ionospheric electron density at a much higher spatial resolution than observed by the EISCAT_3D radar.
Thomas B. Leyser, Tima Sergienko, Urban Brändström, Björn Gustavsson, and Michael T. Rietveld
Ann. Geophys., 41, 589–600, https://doi.org/10.5194/angeo-41-589-2023, https://doi.org/10.5194/angeo-41-589-2023, 2023
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Powerful radio waves transmitted into the ionosphere from the ground were used to study electron energization in the pumped ionospheric plasma turbulence, by detecting optical emissions from atomic oxygen. Our results obtained with the EISCAT (European Incoherent Scatter Scientific Association) facilities in northern Norway and optical detection with the ALIS (Auroral Large Imaging System) in northern Sweden suggest that long-wavelength upper hybrid waves are important in accelerating electrons.
Mizuki Fukizawa, Yoshimasa Tanaka, Yasunobu Ogawa, Keisuke Hosokawa, Tero Raita, and Kirsti Kauristie
Ann. Geophys., 41, 511–528, https://doi.org/10.5194/angeo-41-511-2023, https://doi.org/10.5194/angeo-41-511-2023, 2023
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We use computed tomography to reconstruct the three-dimensional distributions of the Hall and Pedersen conductivities of pulsating auroras, a key research target for understanding the magnetosphere–ionosphere coupling process. It is suggested that the high-energy electron precipitation associated with pulsating auroras may have a greater impact on the closure of field-aligned currents in the ionosphere than has been previously reported.
Liisa Juusola, Ari Viljanen, Noora Partamies, Heikki Vanhamäki, Mirjam Kellinsalmi, and Simon Walker
Ann. Geophys., 41, 483–510, https://doi.org/10.5194/angeo-41-483-2023, https://doi.org/10.5194/angeo-41-483-2023, 2023
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At times when auroras erupt on the sky, the magnetic field surrounding the Earth undergoes rapid changes. On the ground, these changes can induce harmful electric currents in technological conductor networks, such as powerlines. We have used magnetic field observations from northern Europe during 28 such events and found consistent behavior that can help to understand, and thus predict, the processes that drive auroras and geomagnetically induced currents.
Masatoshi Yamauchi and Urban Brändström
Geosci. Instrum. Method. Data Syst., 12, 71–90, https://doi.org/10.5194/gi-12-71-2023, https://doi.org/10.5194/gi-12-71-2023, 2023
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Potential users of all-sky aurora images even include power companies, tourists, and aurora enthusiasts. However, these potential users are normally not familiar with interpreting these images. To make them comprehensive for more users, we developed an automatic evaluation system of auroral activity level. The method involves two steps: first making a simple set of numbers that describes the auroral activity and then further simplifying them into several levels (Level 6 is an auroral explosion).
Anton Goertz, Noora Partamies, Daniel Whiter, and Lisa Baddeley
Ann. Geophys., 41, 115–128, https://doi.org/10.5194/angeo-41-115-2023, https://doi.org/10.5194/angeo-41-115-2023, 2023
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Poleward moving auroral forms (PMAFs) are specific types of aurora believed to be the signature of the connection of Earth's magnetic field to that of the sun. In this paper, we discuss the evolution of PMAFs with regard to their auroral morphology as observed in all-sky camera images. We interpret different aspects of this evolution in terms of the connection dynamics between the magnetic fields of Earth and the sun. This sheds more light on the magnetic interaction between the sun and Earth.
Daniel K. Whiter, Noora Partamies, Björn Gustavsson, and Kirsti Kauristie
Ann. Geophys., 41, 1–12, https://doi.org/10.5194/angeo-41-1-2023, https://doi.org/10.5194/angeo-41-1-2023, 2023
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We measured the height of green and blue aurorae using thousands of camera images recorded over a 7-year period. Both colours are typically brightest at about 114 km altitude. When they peak at higher altitudes the blue aurora is usually higher than the green aurora. This information will help other studies which need an estimate of the auroral height. We used a computer model to explain our observations and to investigate how the green aurora is produced.
Carsten Baumann, Antti Kero, Shikha Raizada, Markus Rapp, Michael P. Sulzer, Pekka T. Verronen, and Juha Vierinen
Ann. Geophys., 40, 519–530, https://doi.org/10.5194/angeo-40-519-2022, https://doi.org/10.5194/angeo-40-519-2022, 2022
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The Arecibo radar was used to probe free electrons of the ionized atmosphere between 70 and 100 km altitude. This is also the altitude region were meteors evaporate and form secondary particulate matter, the so-called meteor smoke particles (MSPs). Free electrons attach to these MSPs when the sun is below the horizon and cause a drop in the number of free electrons, which are the subject of these measurements. We also identified a different number of free electrons during sunset and sunrise.
Mizuki Fukizawa, Takeshi Sakanoi, Yoshimasa Tanaka, Yasunobu Ogawa, Keisuke Hosokawa, Björn Gustavsson, Kirsti Kauristie, Alexander Kozlovsky, Tero Raita, Urban Brändström, and Tima Sergienko
Ann. Geophys., 40, 475–484, https://doi.org/10.5194/angeo-40-475-2022, https://doi.org/10.5194/angeo-40-475-2022, 2022
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The pulsating auroral generation mechanism has been investigated by observing precipitating electrons using rockets or satellites. However, it is difficult for such observations to distinguish temporal changes from spatial ones. In this study, we reconstructed the horizontal 2-D distribution of precipitating electrons using only auroral images. The 3-D aurora structure was also reconstructed. We found that there were both spatial and temporal changes in the precipitating electron energy.
Derek McKay, Juha Vierinen, Antti Kero, and Noora Partamies
Geosci. Instrum. Method. Data Syst., 11, 25–35, https://doi.org/10.5194/gi-11-25-2022, https://doi.org/10.5194/gi-11-25-2022, 2022
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When radio waves from our galaxy enter the Earth's atmosphere, they are absorbed by electrons in the upper atmosphere. It was thought that by measuring the amount of absorption, it would allow the height of these electrons in the atmosphere to be determined. If so, this would have significance for future instrument design. However, this paper demonstrates that it is not possible to do this, but it does explain how multiple-frequency measurements can nevertheless be useful.
Fasil Tesema, Noora Partamies, Daniel K. Whiter, and Yasunobu Ogawa
Ann. Geophys., 40, 1–10, https://doi.org/10.5194/angeo-40-1-2022, https://doi.org/10.5194/angeo-40-1-2022, 2022
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In this study, we present the comparison between an auroral model and EISCAT radar electron densities during pulsating aurorae. We test whether an overpassing satellite measurement of the average energy spectrum is a reasonable estimate for pulsating aurora electron precipitation. When patchy pulsating aurora is dominant in the morning sector, the overpass-averaged spectrum is found to be a reasonable estimate – but not when there is a mix of pulsating aurora types in the post-midnight sector.
Daniel K. Whiter, Hanna Sundberg, Betty S. Lanchester, Joshua Dreyer, Noora Partamies, Nickolay Ivchenko, Marco Zaccaria Di Fraia, Rosie Oliver, Amanda Serpell-Stevens, Tiffany Shaw-Diaz, and Thomas Braunersreuther
Ann. Geophys., 39, 975–989, https://doi.org/10.5194/angeo-39-975-2021, https://doi.org/10.5194/angeo-39-975-2021, 2021
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This paper presents an analysis of high-resolution optical and radar observations of a phenomenon called fragmented aurora-like emissions (FAEs) observed close to aurora in the high Arctic. The observations suggest that FAEs are not caused by high-energy electrons or protons entering the atmosphere along Earth's magnetic field and are, therefore, not aurora. The speeds of the FAEs and their internal dynamics were measured and used to evaluate theories for how the FAEs are produced.
Cited articles
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Dreyer, J., Partamies, N., Whiter, D., Ellingsen, P. G., Baddeley, L., and Buchert, S. C.: Characteristics of fragmented aurora-like emissions (FAEs) observed on Svalbard, Ann. Geophys., 39, 277–288, https://doi.org/10.5194/angeo-39-277-2021, 2021. a, b, c, d
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Gillies, D. M., Donovan, E., Hampton, D., Liang, J., Connors, M., Nishimura, Y., Gallardo-Lacourt, B., and Spanswick, E.: First Observations From the TREx Spectrograph: The Optical Spectrum of STEVE and the Picket Fence Phenomena, Geophysical Research Letters, 46, 7207–7213, https://doi.org/10.1029/2019GL083272, 2019. a, b
Gillies, D. M., Liang, J., Gallardo-Lacourt, B., and Donovan, E.: New Insight Into the Transition From a SAR Arc to STEVE, Geophysical Research Letters, 50, e2022GL101205, https://doi.org/10.1029/2022GL101205, 2023. a
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Kero, A., Vierinen, J., McKay-Bukowski, D., Enell, C.-F., Sinor, M., Roininen, L., and Ogawa, Y.: Ionospheric electron density profiles inverted from a spectral riometer measurement, Geophysical Research Letters, 41, 5370–5375, https://doi.org/10.1002/2014GL060986, 2014. a
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Lanchester, B. S., Rees, M. H., Lummerzheim, D., Otto, A., Sedgemore-Schulthess, K. J. F., Zhu, H., and McCrea, I. W.: Ohmic heating as evidence for strong field-aligned currents in filamentary aurora, Journal of Geophysical Research: Space Physics, 106, 1785–1794, https://doi.org/10.1029/1999JA000292, 2001. a
Liang, J. and Donovan, E.: Quantum Calculation of the Vibrational Excitation of Nitrogen Molecules by Fast Ions: Can It Contribute to STEVE Formation?, Geophysical Research Letters, 51, e2024GL110986, https://doi.org/10.1029/2024GL110986, 2024. a
Liang, J., Donovan, E., Connors, M., Gillies, D., St-Maurice, J. P., Jackel, B., Gallardo-Lacourt, B., Spanswick, E., and Chu, X.: Optical Spectra and Emission Altitudes of Double-Layer STEVE: A Case Study, Geophysical Research Letters, 46, 13630–13639, https://doi.org/10.1029/2019GL085639, 2019. a
MacDonald, E. A., Donovan, E., Nishimura, Y., Case, N. A., Gillies, D. M., Gallardo-Lacourt, B., Archer, W. E., Spanswick, E. L., Bourassa, N., Connors, M., Heavner, M., Jackel, B., Kosar, B., Knudsen, D. J., Ratzlaff, C., and Schofield, I.: New science in plain sight: Citizen scientists lead to the discovery of optical structure in the upper atmosphere, Science Advances, 4, eaaq0030, https://doi.org/10.1126/sciadv.aaq0030, 2018. a, b
Martinis, C., Nishimura, Y., Wroten, J., Bhatt, A., Dyer, A., Baumgardner, J., and Gallardo-Lacourt, B.: First Simultaneous Observation of STEVE and SAR Arc Combining Data From Citizen Scientists, 630.0 nm All-Sky Images, and Satellites, Geophysical Research Letters, 48, e2020GL092169, https://doi.org/10.1029/2020GL092169, 2021. a
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Mishin, E. and Streltsov, A.: STEVE and the Picket Fence: Evidence of Feedback-Unstable Magnetosphere-Ionosphere Interaction, Geophysical Research Letters, 46, 14247–14255, https://doi.org/10.1029/2019GL085446, 2019. a
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Nanjo, S., Hofstra, G. A., Shiokawa, K., Shinbori, A., Nozawa, S., and Hosokawa, K.: Post-midnight purple arc and patches appeared on the high latitude part of the auroral oval: Dawnside counterpart of STEVE?, Earth, Planets and Space, 76, 55, https://doi.org/10.1186/s40623-024-01995-9, 2024. a
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Short summary
During the New Year’s Day storm of 2025, we observed rare auroral features: thin, short-lived green stripes and a “picket fence” near the poleward edge of the auroral oval. Using ground cameras and satellites, we found that the stripes sometimes appeared at widely separated longitudes at the same time and often tracked the motion of nearby red auroras. Some stripes were aligned with the magnetic field, while others were not, implying that multiple local processes contribute to their generation.
During the New Year’s Day storm of 2025, we observed rare auroral features: thin, short-lived...
