Articles | Volume 44, issue 1
https://doi.org/10.5194/angeo-44-1-2026
© 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-44-1-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Regular paper
| 
12 Jan 2026
Regular paper |
| 12 Jan 2026
| 12 Jan 2026
Time-dependent modeling of Alfvénic precipitation observed in the ionosphere
Department of Physics and Technology, UiT The Arctic University of Norway, Tromsø, Norway
Andres Spicher
Department of Physics and Technology, UiT The Arctic University of Norway, Tromsø, Norway
Björn Gustavsson
Department of Physics and Technology, UiT The Arctic University of Norway, Tromsø, Norway
James Clemmons
Department of Physics and Astronomy, University of New Hampshire, Durham, NH, USA
Robert Pfaff
NASA Goddard Space Flight Center, Greenbelt, MD, United States
Douglas Rowland
NASA Goddard Space Flight Center, Greenbelt, MD, United States
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Etienne Gavazzi, Andres Spicher, Björn Gustavsson, Juha Vierinen, James Clemmons, Robert Pfaff, and Douglas Rowland
EGUsphere, https://doi.org/10.5194/egusphere-2026-2126, https://doi.org/10.5194/egusphere-2026-2126, 2026
This preprint is open for discussion and under review for Annales Geophysicae (ANGEO).
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Auroras are caused by energetic electrons entering the upper atmosphere. For the smallest and most dynamic auroras, scientists think electrons are accelerated by waves (called Alfvén waves) thousands of kilometers above Earth. In this paper, we analyse data from a rocket that flew through an aurora, applying existing and new techniques to estimate where the acceleration took place. Our results match theory, and we show how they can be used to study conditions in the near-Earth space environment.
Etienne Gavazzi, Andres Spicher, Björn Gustavsson, Juha Vierinen, James Clemmons, Robert Pfaff, and Douglas Rowland
EGUsphere, https://doi.org/10.5194/egusphere-2026-2126, https://doi.org/10.5194/egusphere-2026-2126, 2026
This preprint is open for discussion and under review for Annales Geophysicae (ANGEO).
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Auroras are caused by energetic electrons entering the upper atmosphere. For the smallest and most dynamic auroras, scientists think electrons are accelerated by waves (called Alfvén waves) thousands of kilometers above Earth. In this paper, we analyse data from a rocket that flew through an aurora, applying existing and new techniques to estimate where the acceleration took place. Our results match theory, and we show how they can be used to study conditions in the near-Earth space environment.
Theresa Rexer, Björn Gustavsson, Juha Vierinen, Andres Spicher, Devin Ray Huyghebaert, Andreas Kvammen, Robert Gillies, and Asti Bhatt
Geosci. Instrum. Method. Data Syst., 15, 127–139, https://doi.org/10.5194/gi-15-127-2026, https://doi.org/10.5194/gi-15-127-2026, 2026
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We present a second-level calibration method for electron density measurements from multi-beam incoherent scatter radars. It is based on the well-known Flat field correction method used in imaging and photography. The method improves data quality and useability as it accounts for unaccounted and unpredictable variations in the radar system. This is valuable for studies where inter-beam calibration is important such as studies of polar cap patches, plasma irregularities and turbulence.
Margaretha Myrvang and Björn Johan Gustavsson
EGUsphere, https://doi.org/10.5194/egusphere-2026-1118, https://doi.org/10.5194/egusphere-2026-1118, 2026
This preprint is open for discussion and under review for Annales Geophysicae (ANGEO).
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This is the second of two papers. The first paper demonstrate that the electron distribution becomes non-Maxwellian during radio wave heating. Electron cooling rates are macroscopic properties of the electron gas, where electrons transfer some of their kinetic energy through collisions with neutrals and ions, and can be determined by integrating over the electron distribution. Any changes in the electron distribution affect the cooling rates.
Margaretha Myrvang and Björn Gustavsson
EGUsphere, https://doi.org/10.5194/egusphere-2026-1117, https://doi.org/10.5194/egusphere-2026-1117, 2026
This preprint is open for discussion and under review for Annales Geophysicae (ANGEO).
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This paper investigate how radio wave heating affect the electron distribution in the D region. Radio wave heating can lead to absorption of radio wave energy by electrons, thereby increasing the temperature. Electrons are cooled by inelastic collisions with the neutrals atmosphere, affecting the electron distribution since electrons lose energy by exciting different states in neutrals. Thus, electrons are redistributed to lower energies, which changes the shape of the electron distribution.
Oliver Stalder, Björn Gustavsson, and Ilkka Virtanen
Ann. Geophys., 44, 123–135, https://doi.org/10.5194/angeo-44-123-2026, https://doi.org/10.5194/angeo-44-123-2026, 2026
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The rapid changes in ion composition during auroral are dynamically modeled by integrating the coupled continuity equations for 15 ionospheric species. The effect of the ionospheric variation on the inversion of incoherent scatter radar (ISR) electron density profiles to differential energy spectra of precipitating electrons is studied. A systematic overestimation at high electron energies can be removed using a dynamic model. Comparisons are made with static and steady-state ionospheric models.
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.
Ingeborg Frøystein, Andres Spicher, and Kjellmar Oksavik
EGUsphere, https://doi.org/10.5194/egusphere-2025-6188, https://doi.org/10.5194/egusphere-2025-6188, 2025
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The dayside auroral region is a highly dynamic region of the ionosphere that is influenced by the coupling between the solar wind, magnetosphere, and ionosphere. In this paper, we illustrate this dynamic nature and present a quantitative analysis of both altitudinal and latitudinal variation within the region. In addition, ionospheric parameters on closed field lines, along the open-closed field line boundary and in the polar cap are statistically compared.
Spencer Mark Hatch, Ilkka Virtanen, Karl Magnus Laundal, Habtamu Wubie Tesfaw, Juha Vierinen, Devin Ray Huyghebaert, Andres Spicher, and Jens Christian Hessen
Ann. Geophys., 43, 633–649, https://doi.org/10.5194/angeo-43-633-2025, https://doi.org/10.5194/angeo-43-633-2025, 2025
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This study addresses the design of next-generation incoherent scatter radar experiments used to study the ionosphere, particularly with systems that have multiple sites. We have developed a method to estimate uncertainties of measurements of plasma density, temperature, and ion drift. Our method is open-source, and helps to optimize radar configurations and assess the effectiveness of an experiment. This method ultimately serves to enhance our understanding of Earth's space environment.
Devin Huyghebaert, Juha Vierinen, Björn Gustavsson, Ralph Latteck, Toralf Renkwitz, Marius Zecha, Claudia C. Stephan, J. Federico Conte, Daniel Kastinen, Johan Kero, and Jorge L. Chau
EGUsphere, https://doi.org/10.5194/egusphere-2025-2323, https://doi.org/10.5194/egusphere-2025-2323, 2025
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The phenomena of meteors occurs at altitudes of 60–120 km and can be used to measure the neutral atmosphere. We use a large high power radar system in Norway (MAARSY) to determine changes to the atmospheric density between the years of 2016–2023 at altitudes of 85–115 km. The same day-of-year is compared, minimizing changes to the measurements due to factors other than the atmosphere. This presents a novel method by which to obtain atmospheric neutral density variations.
Devin Huyghebaert, Björn Gustavsson, Juha Vierinen, Andreas Kvammen, Matthew Zettergren, John Swoboda, Ilkka Virtanen, Spencer M. Hatch, and Karl M. Laundal
Ann. Geophys., 43, 99–113, https://doi.org/10.5194/angeo-43-99-2025, https://doi.org/10.5194/angeo-43-99-2025, 2025
Short summary
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The EISCAT_3D radar is a new ionospheric radar under construction in the Fennoscandia region. The radar will make measurements of plasma characteristics at altitudes above approximately 60 km. The capability of the system to make these measurements at spatial scales of less than 100 m using multiple digitised signals from each of the radar antenna panels is highlighted. There are many ionospheric small-scale processes that will be further resolved using the techniques discussed here.
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.
Johann Stamm, Juha Vierinen, Björn Gustavsson, and Andres Spicher
Ann. Geophys., 41, 55–67, https://doi.org/10.5194/angeo-41-55-2023, https://doi.org/10.5194/angeo-41-55-2023, 2023
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The study of some ionospheric events benefit from the knowledge of how the physics varies over a volume and over time. Examples are studies of aurora or energy deposition. With EISCAT3D, measurements of ion velocity vectors in a volume will be possible for the first time. We present a technique that uses a set of such measurements to estimate electric field and neutral wind. The technique relies on adding restrictions to the estimates. We successfully consider restrictions based on physics.
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
Short summary
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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.
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.
Johann Stamm, Juha Vierinen, and Björn Gustavsson
Ann. Geophys., 39, 961–974, https://doi.org/10.5194/angeo-39-961-2021, https://doi.org/10.5194/angeo-39-961-2021, 2021
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Measurements of the electric field and neutral wind in the ionosphere are important for understanding energy flows or electric currents. With incoherent scatter radars (ISRs), we can measure the velocity of the ions, which depends on both the electrical field and the neutral wind. In this paper, we investigate methods to use ISR data to find reasonable values for both parameters. We find that electric field can be well measured down to 125 km height and neutral wind below this height.
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Short summary
Auroral precipitation refers to energetic particles that come down into the upper part of our atmosphere, the ionosphere. There, they collide with atoms and molecules and transfer some of their energy, causing aurora. The most rapid time-variation of this energy deposition and its consequences on the ionosphere are not fully understood. We show here that one can use a new model to study auroral precipitation on sub-second timescales and advance our understanding about small-scale dynamic aurora.
Auroral precipitation refers to energetic particles that come down into the upper part of our...
