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Krämer, E., Koller, F., Suni, J., LaMoury, A. T., Pöppelwerth, A., Glebe, G., . . . Vörös, Z. (2025). Jets downstream of collisionless shocks: recent discoveries and challenges. Space Science Reviews, 221(1), Article ID 4.
Open this publication in new window or tab >>Jets downstream of collisionless shocks: recent discoveries and challenges
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2025 (English)In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 221, no 1, article id 4Article in journal (Refereed) Published
Abstract [en]

Plasma flows with enhanced dynamic pressure, known as magnetosheath jets, are often found downstream of collisionless shocks. As they propagate through the magnetosheath, they interact with the surrounding plasma, shaping its properties, and potentially becoming geoeffective upon reaching the magnetopause. In recent years (since 2016), new research has produced vital results that have significantly enhanced our understanding on many aspects of jets. In this review, we summarise and discuss these findings. Spacecraft and ground-based observations, as well as global and local simulations, have contributed greatly to our understanding of the causes and effects of magnetosheath jets. First, we discuss recent findings on jet occurrence and formation, including in other planetary environments. New insights into jet properties and evolution are then examined using observations and simulations. Finally, we review the impact of jets upon interaction with the magnetopause and subsequent consequences for the magnetosphere-ionosphere system. We conclude with an outlook and assessment on future challenges. This includes an overview on future space missions that may prove crucial in tackling the outstanding open questions on jets in the terrestrial magnetosheath as well as other planetary and shock environments.

Place, publisher, year, edition, pages
Springer Nature, 2025
Keywords
Bow shock, Foreshock, Magnetopause, Magnetosheath, Magnetosheath jets, Solar wind
National Category
Astronomy, Astrophysics and Cosmology Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-234023 (URN)10.1007/s11214-024-01129-3 (DOI)001385158800001 ()39735479 (PubMedID)2-s2.0-85213531013 (Scopus ID)
Available from: 2025-01-14 Created: 2025-01-14 Last updated: 2025-01-14Bibliographically approved
Stenberg Wieser, G., André, M., Nilsson, H., Edberg, N., Persson, M., Rojas Mata, S., . . . Futaana, Y. (2024). Estimating the possible ion heating caused by Alfvén waves at Venus. Journal of Geophysical Research - Space Physics, 129(12), Article ID e2024JA032865.
Open this publication in new window or tab >>Estimating the possible ion heating caused by Alfvén waves at Venus
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2024 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 129, no 12, article id e2024JA032865Article in journal (Refereed) Published
Abstract [en]

In the Earth's magnetosphere wave-particle interaction is a major ion energization process, playing an important role for the atmospheric escape. A common type of ion heating is associated with low-frequency broadband electric wave fields. For such waves the energy is not concentrated to a certain narrow frequency range and exhibits no peaks or dips in a power spectrum. If there are enough fluctuations close to the ion gyrofrequency the electric field may still come in resonance with gyrating ions and heat them perpendicular to the background magnetic field. We perform a proof-of-concept study to investigate if this heating mechanism may contibute significantly to the energization of planetary ions also in the induced magnetosphere of Venus. We assume Alfvénic fluctuations and estimate the electric field spectral density based on magnetic field observations. We find typical estimated electric spectral densities of a few (Formula presented.) /Hz close to Venus. This corresponds to a heating rate of a few eV/s. We consider an available interaction time of (Formula presented.) 300 s and conclude that this mechanism could increase the energy of an oxygen ion by about a keV. Observed thermal energies are in the range 100–1,000 eV and thus, resonant wave heating may also be important at Venus.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2024
Keywords
ion energization, resonant heating, Venus, wave-particle interaction
National Category
Fusion, Plasma and Space Physics Geophysics
Identifiers
urn:nbn:se:umu:diva-233330 (URN)10.1029/2024JA032865 (DOI)001372415600001 ()2-s2.0-85211761537 (Scopus ID)
Funder
Swedish Institute, 79/19Swedish National Space Board
Available from: 2025-01-02 Created: 2025-01-02 Last updated: 2025-01-02Bibliographically approved
Möslinger, A., Gunell, H., Nilsson, H., Fatemi, S. & Stenberg Wieser, G. (2024). Explaining the evolution of ion velocity distributions at a low activity comet. Journal of Geophysical Research - Space Physics, 129(9), Article ID e2024JA032757.
Open this publication in new window or tab >>Explaining the evolution of ion velocity distributions at a low activity comet
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2024 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 129, no 9, article id e2024JA032757Article in journal (Refereed) Published
Abstract [en]

At a low activity comet the plasma is distributed in an asymmetric way. The hybrid simulation code Amitis is used to look at the spatial evolution of ion velocity distribution functions (VDFs), from the upstream solar wind (SW) to within the comet magnetosphere where the SW is heavily mass-loaded by the cometary plasma. We find that the spatial structures of the ions and fields form a highly asymmetric induced magnetosphere. The VDFs of SW and cometary ions vary drastically for different locations in the comet magnetosphere. The shape of the VDFs differ for different species. The SW protons show high anisotropies that occasionally resemble partial rings, in particular at small cometocentric distances. A second, decoupled, proton population is also found. Solar wind alpha particles show similar anisotropies, although less pronounced and at different spatial scales. The VDFs of cometary ions are mostly determined by the structure of the electric field. We perform supplementary dynamic particle backtracing to understand the flow patterns of SW ions that lead to these anisotropic distributions. This tracing is needed to understand the origin of cometary ions in a given part of the comet magnetosphere. The particle tracing also aids in interpreting observed VDFs and relating them to spatial features in the electric and magnetic fields of the comet environment.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2024
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-230125 (URN)10.1029/2024JA032757 (DOI)001314615300001 ()2-s2.0-85204575834 (Scopus ID)
Funder
Swedish National Space Board, 132/19Swedish National Space Board, 2023‐00208Swedish National Space Board, 2022‐00183
Available from: 2024-10-14 Created: 2024-10-14 Last updated: 2024-10-17Bibliographically approved
Gunell, H., Goetz, C. & Fatemi, S. (2024). Impact of radial interplanetary magnetic fields on the inner coma of comet 67P/Churyumov-Gerasimenko: Hybrid simulations of the plasma environment. Astronomy and Astrophysics, 682, Article ID A62.
Open this publication in new window or tab >>Impact of radial interplanetary magnetic fields on the inner coma of comet 67P/Churyumov-Gerasimenko: Hybrid simulations of the plasma environment
2024 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 682, article id A62Article in journal (Refereed) Published
Abstract [en]

Context. The direction of the interplanetary magnetic field determines the nature of the interaction between a Solar System object and the solar wind. For comets, it affects the formation of both a bow shock and other plasma boundaries, as well as mass-loading. Around the nucleus of a comet, there is a diamagnetic cavity, where the magnetic field is negligible. Observations by the Rosetta spacecraft have shown that, most of the time, the diamagnetic cavity is located within a solar-wind ion cavity, which is devoid of solar wind ions. However, solar wind ions have been observed inside the diamagnetic cavity on several occasions. Understanding what determines whether or not the solar wind can reach the diamagnetic cavity also advances our understanding of cometsolar wind interaction in general.

Aims. We aim to determine the influence of an interplanetary magnetic field directed radially out from the Sun that is, parallel to the solar wind velocity on the cometsolar wind interaction. In particular, we explore the possibility of solar wind protons entering the diamagnetic cavity under radial field conditions.

Methods. We performed global hybrid simulations of comet 67P/Churyumov-Gerasimenko using the simulation code Amitis for two different interplanetary magnetic field configurations and compared the results to observations made by the Rosetta spacecraft.

Results. We find that, when the magnetic field is parallel to the solar wind velocity, no bow shock forms and the solar wind ions are able to enter the diamagnetic cavity. A solar wind ion wake still forms further downstream in this case.

Conclusions. The solar wind can enter the diamagnetic cavity if the interplanetary magnetic field is directed radially from the Sun, and this is in agreement with observations made by instruments on board the Rosetta spacecraft.

Place, publisher, year, edition, pages
EDP Sciences, 2024
Keywords
Comets: general, Comets: individual: 67P/Churyumov-Gerasimenko, Methods: numerical, Plasmas
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-221400 (URN)10.1051/0004-6361/202348186 (DOI)001158013900006 ()2-s2.0-85184848705 (Scopus ID)
Funder
Swedish National Space Board, 108/18Swedish National Space Board, 115/18Swedish Research Council, 2018-03454
Available from: 2024-02-26 Created: 2024-02-26 Last updated: 2024-02-26Bibliographically approved
Gunell, H., Schaeffer, D., Goetz, C., Cruz, F., Wedlund, C. S., Nilsson, H., . . . Edberg, N. (2024). Plasma physics at comets: what can we learn from laboratory experiments?. In: 2024 International Conference on Electromagnetics in Advanced Applications (ICEAA): . Paper presented at 2024 International Conference on Electromagnetics in Advanced Applications, (ICEAA), Lisboa, Portugal, 2-6 September 2024 (pp. 163-163). IEEE (2024)
Open this publication in new window or tab >>Plasma physics at comets: what can we learn from laboratory experiments?
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2024 (English)In: 2024 International Conference on Electromagnetics in Advanced Applications (ICEAA), IEEE, 2024, no 2024, p. 163-163Conference paper, Published paper (Refereed)
Abstract [en]

Diamagnetic cavities at comets were predicted already in the 1960s [1], and then observed at comet lP/Halley by the ESA/Giotto spacecraft in 1986 [2]. Recently, the ESA/Rosetta spacecraft spent two years orbiting comet 67P/Churyumov-Gerasimenko and encountered the diamagnetic cavity of comet 67P more than 700 times [3, 4]. Most encounters lasted a few minutes, with the duration varying from a few seconds up to more than 30 minutes. As the spacecraft moved very slowly (~lms-1), it can be considered stationary with respect to the plasma. Therefore, the quick succession of detections indicates that the boundary of the diamagnetic cavity moved over the spacecraft. Figure 1 (left) shows three diamagnetic cavity signatures observed with the plasma instruments on Rosetta on 16 September 2015 when the comet was close to perihelion. Rosetta was in the diamagnetic cavity during the periods of nearly zero magnetic field (marked by the coloured regions). Outside the cavity, the plasma was often characterised by a series of asymmetric, steepened waves which are visible in the magnetic field, as well as in the plasma density [5]. Since all observations to date have been made using a single spacecraft, the shape of the diamagnetic cavity boundary cannot be well constrained by measurements. However, it has been suggested, based on wave observations, that bulges on the cavity boundary move past the spacecraft, causing the latter to quickly move in and out of the cavity [6].

Place, publisher, year, edition, pages
IEEE, 2024
Series
International Conference on Electromagnetics in Advanced Applications, ISSN 2835-1355, E-ISSN 2766-2284
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-232244 (URN)10.1109/ICEAA61917.2024.10701783 (DOI)2-s2.0-85208714504 (Scopus ID)9798350360981 (ISBN)9798350360974 (ISBN)
Conference
2024 International Conference on Electromagnetics in Advanced Applications, (ICEAA), Lisboa, Portugal, 2-6 September 2024
Available from: 2024-11-28 Created: 2024-11-28 Last updated: 2024-11-28Bibliographically approved
Edberg, N., Eriksson, A., Vigren, E., Nilsson, H., Gunell, H., Götz, C., . . . De Keyser, J. (2024). Scale size of cometary bow shocks. Astronomy and Astrophysics, 682, Article ID A51.
Open this publication in new window or tab >>Scale size of cometary bow shocks
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2024 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 682, article id A51Article in journal (Refereed) Published
Abstract [en]

Context. In past decades, several spacecraft have visited comets to investigate their plasma environments. In the coming years, Comet Interceptor will make yet another attempt. This time, the target comet and its outgassing activity are unknown and may not be known before the spacecraft has been launched into its parking orbit, where it will await a possible interception. If the approximate outgassing rate can be estimated remotely when a target has been identified, it is desirable to also be able to estimate the scale size of the plasma environment, defined here as the region bound by the bow shock.

Aims. This study aims to combine previous measurements and simulations of cometary bow shock locations to gain a better understanding of how the scale size of cometary plasma environments varies. We compare these data with models of the bow shock size, and we furthermore provide an outgassing rate-dependent shape model of the bow shock. We then use this to predict a range of times and cometocentric distances for the crossing of the bow shock by Comet Interceptor, together with expected plasma density measurements along the spacecraft track.

Methods. We used data of the location of cometary bow shocks from previous spacecraft missions, together with simulation results from previously published studies. We compared these results with an existing model of the bow shock stand-off distance and expand on this to provide a shape model of cometary bow shocks. The model in particular includes the cometary outgassing rate, but also upstream solar wind conditions, ionisation rates, and the neutral flow velocity.

Results. The agreement between the gas-dynamic model and the data and simulation results is good in terms of the stand-off distance of the bow shock as a function of the outgassing rate. For outgassing rates in the range of 1027-1031-s-1, the scale size of cometary bow shocks can vary by four orders of magnitude, from about 102 km to 106 km, for an ionisation rate, flow velocity, and upstream solar wind conditions typical of those at 1 AU. The proposed bow shock shape model shows that a comet plasma environment can range in scale size from the plasma environment of Mars to about half of that of Saturn.

Conclusions. The model-data agreement allows for the planning of upcoming spacecraft comet encounters, such as that of Comet Interceptor, when a target has been identified and its outgassing rate is determined. We conclude that the time a spacecraft can spend within the plasma environment during a flyby can range from minutes to days, depending on the comet that is visited and on the flyby speed. However, to capture most of the comet plasma environment, including pick-up ions and upstream plasma waves, and to ensure the highest possible scientific return, measurements should still start well upstream of the expected bow shock location. From the plasma perspective, the selected target should preferably be an active comet with the lowest possible flyby velocity.

Place, publisher, year, edition, pages
EDP Sciences, 2024
Keywords
Comets: general, Plasmas
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-220870 (URN)10.1051/0004-6361/202346566 (DOI)2-s2.0-85183994991 (Scopus ID)
Funder
Swedish Research Council, 2020-03962
Available from: 2024-02-19 Created: 2024-02-19 Last updated: 2024-02-19Bibliographically approved
Jones, G. H., Gunell, H. & Ji, H. (2024). The comet interceptor mission. Space Science Reviews, 220, Article ID 9.
Open this publication in new window or tab >>The comet interceptor mission
2024 (English)In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 220, article id 9Article, review/survey (Refereed) Published
Abstract [en]

Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to theexploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. Theobjectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition ofthe gas and dust in the coma, its connection to the nucleus, and the nature of its interactionwith the solar wind? The mission was proposed to the European Space Agency in 2018, andformally adopted by the agency in June 2022, for launch in 2029 together with the Arielmission. Comet Interceptor will take advantage of the opportunity presented by ESA’s FClass call for fast, flexible, low-cost missions to which it was proposed. The call requireda launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage ofthis placement to wait for the discovery of a suitable comet reachable with its minimum ΔV capability of 600 ms−1. Comet Interceptor will be unique in encountering and studying, at anominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that noprevious cometary mission has had, which is to deploy two sub-probes – B1, provided by theJapanese space agency, JAXA, and B2 – that will follow different trajectories through thecoma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 willfollow different chords through the coma at distances of 850 km and 400 km, respectively.The result will be unique, simultaneous, spatially resolved information of the 3-dimensionalproperties of the target comet and its interaction with the space environment. We presentthe mission’s science background leading to these objectives, as well as an overview of thescientific instruments, mission design, and schedule.

Place, publisher, year, edition, pages
Springer Nature, 2024
Keywords
Comets, Spacecraft, Instruments – spaceborne and space research
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:umu:diva-220716 (URN)10.1007/s11214-023-01035-0 (DOI)2-s2.0-85183417097 (Scopus ID)
Funder
The European Space Agency (ESA), 4000136673/21/NL/IB/igThe European Space Agency (ESA), 3-17164/21/NL/GP/pbeSwedish National Space Board, 108/18Swedish National Space Board, 2021-00047EU, Horizon 2020, 802699EU, Horizon Europe, 101079231EU, Horizon Europe, 10051045EU, European Research Council
Available from: 2024-02-09 Created: 2024-02-09 Last updated: 2024-02-09Bibliographically approved
Fatemi, S., Hamrin, M., Krämer, E., Gunell, H., Nordin, G., Karlsson, T. & Goncharov, O. (2024). Unveiling the 3D structure of magnetosheath jets. Monthly notices of the Royal Astronomical Society, 531(4), 4692-4713
Open this publication in new window or tab >>Unveiling the 3D structure of magnetosheath jets
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2024 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 531, no 4, p. 4692-4713Article in journal (Refereed) Published
Abstract [en]

Magnetosheath jets represent localized enhancements in dynamic pressure observed within the magnetosheath. These energetic entities, carrying excess energy and momentum, can impact the magnetopause and disrupt the magnetosphere. Therefore, they play a vital role in coupling the solar wind and terrestrial magnetosphere. However, our understanding of the morphology and formation of these complex, transient events remains incomplete over two decades after their initial observation. Previous studies have relied on oversimplified assumptions, considering jets as elongated cylinders with dimensions ranging from $0.1\, R_{\rm E}$ to $5\, R_{\rm E}$ (Earth radii). In this study, we present simulation results obtained from Amitis, a high-performance hybrid-kinetic plasma framework (particle ions and fluid electrons) running in parallel on graphics processing units (GPUs) for fast and more environmentally friendly computation compared to CPU-based models. Considering realistic scales, we present the first global, three-dimensional (3D in both configuration and velocity spaces) hybrid-kinetic simulation results of the interaction between solar wind plasma and the Earth. Our high-resolution kinetic simulations reveal the 3D structure of magnetosheath jets, showing that jets are far from being simple cylinders. Instead, they exhibit intricate and highly interconnected structures with dynamic 3D characteristics. As they move through the magnetosheath, they wrinkle, fold, merge, and split in complex ways before a subset reaches the magnetopause.

Place, publisher, year, edition, pages
Oxford University Press, 2024
Keywords
planet stars, interactionlanet star, numerical, planets and satellites, terrestrial planets, planets and satellites, magnetic fields, plasmas
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:umu:diva-228720 (URN)10.1093/mnras/stae1456 (DOI)001253786600002 ()
Funder
Swedish National Space Board, 2022-00138Swedish National Space Board, 115/18Swedish Research Council, 2018-03454Swedish Research Council, 2018-03623
Available from: 2024-08-22 Created: 2024-08-22 Last updated: 2024-08-22Bibliographically approved
Östman, S., Gunell, H., Hamrin, M., Opgenoorth, H. J. & Andersson, L. (2024). Width of the quasi-perpendicular bow shock region at Mars. Astronomy and Astrophysics, 689, Article ID A110.
Open this publication in new window or tab >>Width of the quasi-perpendicular bow shock region at Mars
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2024 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 689, article id A110Article in journal (Refereed) Published
Abstract [en]

Aims: We aim to quantify the width of the quasi-perpendicular Martian bow shock region to deepen the understanding of why the width is variable and which factors affect it, and to explore the implications on thermalization.

Methods: To quantify the width, 2074 quasi-perpendicular bow shock crossings from a database were studied. Upstream conditions, such as Mach numbers, dynamic pressure, ion densities, and other factors, were considered. Furthermore, the difference between the downstream and upstream temperature was measured.

Results: We found that the shock region width is correlated with the magnetosonic Mach number, the critical ratio, and the overshoot amplitude. The region was found to be anticorrelated with dynamic pressure. The width is not affected by the upstream ion density of the investigated species or by the upstream temperature. The difference between the downstream and upstream temperature is not affected by the shock region width.

Conclusions: We found that the factors that affect the stand-off distance of the bow shock, such as the magnetosonic Mach number and dynamic pressure, also affect the width. The width is also positively correlated with the overshoot amplitude, indicating that the structures are coupled or that they are affected by largely the same conditions. The lack of a correlation with the ion temperature difference indicates that the shock region width does not affect the ion thermalization.

Place, publisher, year, edition, pages
EDP Sciences, 2024
Keywords
plasmas, shock waves, methods: data analysis, planets and satellites: terrestrial planets, planet-star interactions, planets and satellites: individual: Mars
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:umu:diva-232436 (URN)10.1051/0004-6361/202348385 (DOI)001308055500028 ()2-s2.0-85215438924 (Scopus ID)
Funder
Swedish National Space Board, 108/18Swedish National Space Board, 194/19
Available from: 2024-11-29 Created: 2024-11-29 Last updated: 2025-01-31Bibliographically approved
Moeslinger, A., Nilsson, H., Stenberg Wieser, G., Gunell, H. & Goetz, C. (2023). Indirect observations of electric fields at comet 67P. Journal of Geophysical Research - Space Physics, 128(9), Article ID e2023JA031746.
Open this publication in new window or tab >>Indirect observations of electric fields at comet 67P
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2023 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 128, no 9, article id e2023JA031746Article in journal (Refereed) Published
Abstract [en]

No spacecraft visiting a comet has been equipped with instruments to directly measure the static electric field. However, the electric field can occasionally be estimated indirectly by observing its effects on the ion velocity distribution. We present such observations made by the Rosetta spacecraft on 19 April 2016, 35 km from the nucleus. At this time comet 67P was at a low outgassing rate and the plasma environment was relatively stable. The ion velocity distributions show the cometary ions on the first half of their gyration. We estimate the bulk drift velocity and the gyration speed from the distributions. By using the local measured magnetic field and assuming an E × B drift of the gyrocentre, we get an estimate for the average electric field driving this ion motion. We analyze a period of 13 hr, during which the plasma environment does not change drastically. We find that the average strength of the perpendicular electric field component is 0.21 mV/m. The direction of the electric field is mostly anti-sunward. This is in agreement with previous results based on different methods.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2023
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:umu:diva-214755 (URN)10.1029/2023JA031746 (DOI)2-s2.0-85171655091 (Scopus ID)
Funder
Swedish National Space Board, 132/19Swedish National Space Board, 108/18
Available from: 2023-10-03 Created: 2023-10-03 Last updated: 2024-10-17Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-5379-1158

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