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ST2.4

EDI
Open Session on the Magnetosphere

This open session traditionally invites presentations on all aspects of the Earth’s magnetospheric physics, including the magnetosphere and its boundary layers, magnetosheath, bow shock and foreshock as well as solar wind-magnetosphere-ionosphere coupling. We welcome contributions on various aspects of magnetospheric observations, remote sensing of the magnetosphere’s processes, modelling and theoretical research. The presentations related to the current and planned space missions and to the value-added data services are also encouraged. This session is suitable for any contribution which does not fit more naturally into one of the specialised sessions and for contributions of wide community interest.

Including Arne Richter Award for Outstanding ECS Lecture
Convener: Yulia Bogdanova | Co-convener: C.-Philippe Escoubet
Presentations
| Fri, 27 May, 09:15–11:50 (CEST), 13:20–16:40 (CEST)
 
Room D2

Fri, 27 May, 08:30–10:00

Chairpersons: C.-Philippe Escoubet, Yulia Bogdanova

09:15–09:18
3-minute convener introduction

09:18–09:24
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EGU22-10698
Seth Dorfman et al.

Various types of plasma waves play key roles in magnetospheric physics in contexts ranging from the magnetosphere and its boundary layers to planetary bow shocks and foreshocks.  Due to limited available spacecraft measurements, the waves are often assumed to be plane waves that extend to infinity in all directions. A good example is the Earth's ion foreshock where intrinsically right-hand circularly polarized magnetosonic modes are generated by a fast ion beam. Many prior studies of these waves assume no variation of important physical quantities in the direction perpendicular to wave propagation. We show that Magnetic Gauss's Law implies that this assumption must be violated near the edge of the wave domain. The resulting false signature in the standard Magnetic Gauss's Law calculation of the wave vector orientation may be used to detect the domain edge. We demonstrate this new edge detection method in a simple wave model, a 2-D hybrid Vlasov simulation conducted using the Vlasiator code, and ARTEMIS spacecraft observations. In both the simulation and the spacecraft observations, this new signature is shown to correlate well with a determination of the foreshock edge based on the properties of the fast ion beam.  As the plane wave assumption is widely used in space physics data analysis techniques such as minimum variance analysis, these results may stimulate a reexamination of this assumption in other magnetospheric physics contexts.

This study is supported by NASA Grant 80NSSC20K0801.  Vlasiator is developed by the European Research Council Starting grant 200141-QuESpace, and Consolidator grant GA682068-PRESTISSIMO received by the Vlasiator PI. Vlasiator has also received funding from the Academy of Finland. See www.helsinki.fi/vlasiator

How to cite: Dorfman, S., Zhang, K., Turc, L., and Ganse, U.: Detecting the edges of Earth's ion foreshock using Magnetic Gauss's Law, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10698, https://doi.org/10.5194/egusphere-egu22-10698, 2022.

09:24–09:30
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EGU22-6812
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ECS
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Virtual presentation
Kun Zhang et al.

Large-amplitude ULF waves are usually observed in the foreshock region ahead of quasi-parallel shocks and their generation is driven by the backstreaming ions. In the early phase of the wave growth, the waves are growing with time and traveling in space simultaneously. Therefore, it is very difficult to observe the wave growth properly using single-point measurements such as single spacecraft observations, because the spatial and temporal variations cannot be decoupled. This has also brought difficulties into understanding the detailed physical connection between the foreshock ion properties and the wave properties. In comparison, it is more straightforward to study this problem in global simulations, as simulation results are available everywhere in the foreshock at all times. Here we perform detailed analysis of the ULF wave growth and its relationship with the ion distribution using a Vlasiator simulation (a hybrid-Vlasov code). We calculate the phase speed of the ULF waves and observe the wave growth in the wave frame continuously. We show that the growth rate of the ULF waves decreases with time due to the decrease in beam velocity and the scatter of the ion distribution. And we compare the calculated growth rate with the dispersion relation solved by LEOPARD (a dispersion solver with arbitrary ion distribution input) based on the corresponding ion distribution obtained from the simulation results, and we will discuss the related physical mechanisms such as the ion-ion beam instability when the wave growth can be explained by ion distribution and discuss possible reasons when there is any discrepancy.

How to cite: Zhang, K., Dorfman, S., Turc, L., Ganse, U., Shi, C., and Palmroth, M.: The early-phase growth of ULF waves in the ion foreshock observed in a hybrid-Vlasov simulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6812, https://doi.org/10.5194/egusphere-egu22-6812, 2022.

09:30–09:36
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EGU22-1360
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ECS
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On-site presentation
Anna Salohub et al.

We present a large statistical study of the ultra-low frequency (ULF) waves in the terrestrial foreshock. These waves are excited in the upstream region by energetic ions streaming along the solar wind magnetic field lines connected to the bow shock. Although these waves propagate upstream and grow in the solar wind frame, they are blown down by the solar wind flow and thus their amplitudes would grow toward the bow shock. In our previous study based on ARTEMIS observations, we demonstrated that the statistically determined growth rate is positive but also the cases of a wave decay are frequently observed. We have shown that even if a possible influence of the Moon and its wake is excluded, the growth rate is decreased by non-linear effects leading to a saturation of the wave amplitude. To eliminate this problem, we have selected intervals allowing identification of an initial stage of wave amplitude growth (either in spatial or temporal sense). Our study revealed that the growth rate depends on the wave type being larger for compressive variations of the magnetic field strength and plasma density than for variations of magnetic field components. The analogous study of velocity fluctuations leads to smaller growth rates and we discuss possible causes of this disagreement.

How to cite: Salohub, A., Safrankova, J., and Nemecek, Z.: The foreshock wave activity under quasi radial magnetic field in lunar distances: Statistical study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1360, https://doi.org/10.5194/egusphere-egu22-1360, 2022.

09:36–09:42
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EGU22-7655
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Highlight
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On-site presentation
Lucile Turc et al.

The foreshock, extending upstream of the quasi-parallel shock and populated with shock-reflected particles, is home to intense wave activity in the ultra-low frequency range. The most commonly observed of these waves are the "30-second" waves, fast magnetosonic waves propagating sunward in the plasma rest frame, but carried earthward by the faster solar wind flow. These waves are thought to be the main source of Pc3 magnetic pulsations (10 – 45 s periods) in the dayside magnetosphere, but how the waves can transmit through the bow shock and across the magnetosheath remains unclear. Global hybrid-Vlasov simulations performed with the Vlasiator model provide us with the global view of foreshock wave transmission across near-Earth space. We find that the foreshock waves act as fast-mode pulses hammering periodically the shock, which impulsively sends perturbations in the downstream at the fast-mode speed. These fast-mode disturbances propagate in the magnetosheath all the way to the magnetopause, where they can further transmit into the dayside magnetosphere. The wave propagation across the bow shock appears to be much more complex than the simple "direct transmission" of the foreshock waves which was inferred in early studies. This is due to the complex two-way interactions between the waves and the shock, including shock reformation. We compare our global simulation results with local 1D simulations, and we show that the wave signatures in the downstream strongly depend on the global properties of the shock-magnetosheath system. This emphasises the importance of carrying out global simulations in this context.

How to cite: Turc, L., Roberts, O., Verscharen, D., Dimmock, A., Kajdic, P., Palmroth, M., Pfau-Kempf, Y., Johlander, A., Dubart, M., Kilpua, E., Soucek, J., Takahashi, K., Takahashi, N., Battarbee, M., and Ganse, U.: Transmission of foreshock waves through the Earth’s magnetosheath, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7655, https://doi.org/10.5194/egusphere-egu22-7655, 2022.

09:42–09:48
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EGU22-1745
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ECS
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Niki Xirogiannopoulou et al.

Plasma structures with enhanced density or dynamic pressure, also known as jets or plasmoids, are often observed in Earth’s magnetosheath. Early studies of jets in the magnetosheath have indicated that the jet formation is closely related to processes in the foreshock region. Based on the magnetic field changes, Karlsson et al. (2015) divided the plasmoids into two distinct groups. They observed numbers of “diamagnetic” plasmoids in the foreshock region and suggested that Short Large Amplitude Magnetic Structures (SLAMS) could be a source of both plasmoid types in the magnetosheath. Using measurements by the Magnetospheric Multiscale (MMS) spacecraft we present a statistical analysis of foreshock compressive structures with significantly enhanced density and dynamic pressure. Based on our statistical analysis and previous studies, we discuss features of those structures, their properties, occurrence, evolution, and relation to the magnetosheath jets and plasmoids.

How to cite: Xirogiannopoulou, N., Goncharov, O., Safrankova, J., Nemecek, Z., and Salohub, A.: Foreshock compressive structures and their relations to jet-like events in the magnetosheath, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1745, https://doi.org/10.5194/egusphere-egu22-1745, 2022.

09:48–09:54
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EGU22-4400
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ECS
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On-site presentation
Martin Lindberg et al.

We calculate the change in electron kinetic entropy, ΔSe, across 22 supercritical quasi-perpendicular Earth bow shock crossings observed by the Magnetospheric Multiscale (MMS) mission. The crossings cover a wide range of shock parameters. We calibrate the measured distribution functions measured by MMS to correct for spacecraft potential, secondary electron contamination, lack of measurements at the lowest energies and electron density measurements based on the plasma frequency measurements. The change in electron kinetic entropy displays a strong dependence on the change in electron temperature, ΔTe, and the upstream plasma beta. Shocks with a small upstream plasma beta have a large ΔSe while shocks with high upstream plasma beta have a small ΔSe.

The calculated changes in kinetic entropy, density and temperature are used to estimate the proxy adiabatic index, γe, for each shock crossing. The estimated adiabatic indices are all in the vicinity of 1.6, comparable to that of a monatomic gas with three degrees of freedom.

How to cite: Lindberg, M., Vaivads, A., Raptis, S., Lindqvist, P.-A., Giles, B., and Gershman, D.: Electron Kinetic Entropy Generation at Quasi-perpendicular Collisionless Shocks: Dependence on Shock Parameters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4400, https://doi.org/10.5194/egusphere-egu22-4400, 2022.

09:54–10:00
Discussion time

Fri, 27 May, 10:20–11:50

Chairpersons: Lucile Turc, C.-Philippe Escoubet

10:20–10:26
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EGU22-9956
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Virtual presentation
Harald Kucharek et al.

At the Earth’s bow shock, most of the solar wind’s kinetic energy is partitioned into wave energy, particle acceleration, and heating. Very recent publications provide strong evidence that current sheets at the shock ramp region and downstream participate in the thermalization of the solar wind plasma. Their occurrence varies from single to multiple current sheets. What role do they play in downstream thermalization and ion acceleration?

We studied multiple bow shock crossings into the magnetosheath by the MMS spacecraft with its sophisticated instrumentation, characterizing and quantifying the occurrence of these current sheets, the associated magnetic field wave turbulence, and ion acceleration downstream of the shock. Shock traversals during increasing Mach number/dynamic pressure showed higher wave activity and broader distribution functions with suprathermal tails. Much less suprathermal ions downstream of the shock are observed at shock crossings during decreasing Mach numbers. These MMS observations show that current sheets and field gradients are associated with ion acceleration. The associated turbulence is likely a mediator for energy partition. With increasing Mach numbers, the bow shock moves away from the Sun and compresses the magnetosheath that favours reconnection of currents sheets, stronger electric field gradients and thus ion acceleration. With decreasing Mach numbers, the bow shock moves towards the Sun, becomes blunter, and the sheath region relaxes, making reconnecting current sheets less likely and smoothens field gradients resulting in less acceleration.

How to cite: Kucharek, H., Schwartz, S. J., Gingell, I., Farrugia, C., and Trattner, K. J.: Shock Motion and Ion Acceleration at Current Sheets Downstream of the Bow Earth’ s Bow Shock., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9956, https://doi.org/10.5194/egusphere-egu22-9956, 2022.

10:26–10:32
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EGU22-3219
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On-site presentation
Karlheinz Trattner et al.

The terrestrial bow shock is the boundary between the supersonic solar wind and the terrestrial magnetosphere and converts the kinetic energy of the solar wind into thermal energy, allowing the flow to become subsonic and move past the magnetosphere. Shocks are an important acceleration site for ions and electrons in collisionless plasmas and responsible for much of the particle acceleration in solar, planetary, and astrophysical regions. One of the fundamental outstanding questions of ion acceleration at the quasi-parallel bow shock is which portion of the incoming solar wind ion distribution ultimately becomes the seed population that is subsequently accelerated to high energies.

This talk focuses on distribution functions of protons and alpha particles observed by the HPCA and FPI instruments onboard the MMS satellites during an MMS crossing of the quasi-parallel bow shock. The bow shock transition from the downstream region into the upstream solar wind shows the presence of specularly reflected ions and a distribution at 90 degree pitch angle ions in the shock ramp consistent with shock drift accelerated ions.

How to cite: Trattner, K., Fuselier, S., Schwartz, S., Kucharek, H., Burch, J., Ergun, R., Petrinec, S., and Madanian, H.: Ion Acceleration at the Quasi-Parallel Shock: The Source Distributions of the Diffuse Ions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3219, https://doi.org/10.5194/egusphere-egu22-3219, 2022.

10:32–10:38
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EGU22-2750
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ECS
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On-site presentation
Savvas Raptis et al.

Magnetosheath jets are transient localized structures of enhanced dynamic pressure observed downstream of the Earth’s bow shock. They may exhibit an increase of velocity reaching solar wind levels, while their density is typically much higher than typical magnetosheath and solar wind values. Jets have been associated to several magnetospheric effects such as, magnetopause reconnection, excitations of surface eigenmodes and even direct plasma penetration in the magnetosphere. While their exact origin is unknown, many mechanisms have been proposed. One of the most prominent explanations involves the interaction of solar wind with local inclinations of the bow shock (ripples) while others include solar wind discontinuities, and foreshock structures.

In this work, by using Magnetosphere Multiscale (MMS) we show in-situ observations of a super-magnetosonic magnetosheath jet being generated as a direct result of the bow shock reformation cycle. The observed jet origin appears to be the result of the dynamical evolution of the shock and the emergence of a spatially de-attached compressive magnetic structure that acts as a local shock front. Due to this, the solar wind particles are effectively transferred downstream without experiencing a strong interaction with the shock, which allows compressed high velocity plasma to be observed downstream of the bow shock.

The proposed mechanism does not require external phenomena (e.g., solar wind discontinuities) or specific configuration of the bow shock (e.g., ripples) to take place. On the contrary, it allows the magnetosheath jet phenomenon to directly originate from the dynamical evolution of the quasi-parallel collisionless shock.

How to cite: Raptis, S., Karlsson, T., Vaivads, A., Pollock, C., Plaschke, F., Johlander, A., Trollvik, H., and Lindqvist, P.-A.: High-speed Magnetosheath Jet Generation due to Shock Reformation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2750, https://doi.org/10.5194/egusphere-egu22-2750, 2022.

10:38–10:44
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EGU22-671
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On-site presentation
Primoz Kajdic et al.

Magnetosheath jets are currently an important topic in the field of magnetosheath physics. It is thought that 97 % of the jets are produced by the shock rippling at quasi-parallel shocks. Recently, large statistical studies of magnetosheath jets have been performed, however it is not clear whether rippling also produces jets found downstream of quasi-perpendicular shocks. We analyze four types of events in the quasi-perpendicular magnetosheath with signatures characteristic of magnetosheath jets, namely increased density and/or dynamic pressure, that were not produced by the shock rippling: 1) magnetic flux tubes connected to the quasi-parallel bow-shock, 2) non-reconnecting current sheets, 3) reconnection exhausts and 4) mirror mode waves. The flux tubes are downstream equivalents of the upstream traveling foreshocks. Magnetosheath jets can impact the magnetopause, so knowing the conditions under which they form may enable us to understand their signatures in the magnetosphere.

How to cite: Kajdic, P., Raptis, S., Blanco-Cano, X., and Karlsson, T.: Causes of jets in the quasi-perpendicular magnetosheath, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-671, https://doi.org/10.5194/egusphere-egu22-671, 2022.

10:44–10:50
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EGU22-11999
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ECS
Luis Preisser et al.

Localized enhancements in dynamic pressure observed in the Earth’s magnetosheath (EMS) have been studied since 20 years ago. These structures known as jets can propagate through the EMS transporting mass, momentum and energy being able to reach and perturb the Earth’s magnetopause.
Large scale solar wind (SW) structures called Coronal Mass Ejections (CMEs) travel through the interplanetary medium and depending on their direction they may impact the Earth. How the different SW conditions triggered by the CMEs (upstream side – shock/sheath – magnetic ejecta) change the production of jets in the EMS is a topic that is just beginning to be explored.
In this case study we characterize jets observed by THEMIS A, E and D during a CME passage. We find clear differences in number and size between the jets associated with the different CME regions arriving at the EMS. Comparing WIND and THEMIS data we discuss how these differences are associated with the SW conditions and with different jet generation mechanisms.

How to cite: Preisser, L., Plaschke, F., Koller, F., Temmer, M., and Roberts, O.: Magnetosheath jets during an CME passage: A case study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11999, https://doi.org/10.5194/egusphere-egu22-11999, 2022.

10:50–10:56
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EGU22-6521
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Florian Koller et al.

Magnetosheath jets are dynamic pressure enhancements frequently observed in the Earth’s magnetosheath. They are significant coupling elements between the solar wind and the magnetosphere of the Earth and they can be geoeffective. Jets travel anti-sunward through the magnetosheath and can impact the magnetopause. The generation of these jets is generally linked to processes at the quasi-parallel bow shock and the foreshock. We analyzed how the appearance of these jets is linked to large-scale solar wind (SW) structures, in particular coronal mass ejections (CMEs) and stream interaction regions (SIRs) and their associated high speed streams (HSSs). In our statistical analysis, we use magnetosheath jets detected by the THEMIS spacecraft between 2008 to 2020. We found that the number of detected jets is lower during the passing of CMEs. Significantly more jets are observed during SIRs and HSSs. We analyze the difference in conditions during each SW structure and compare them to the SW conditions measured during the detection of jets. We focus on SW Alfvénic Mach number and IMF cone angle, which affect the presence of the foreshock and the position of the quasi-parallel shock front. We find that jets are unlikely to appear during a mix of low Alfvénic Mach numbers and high cone angles, which are SW conditions often found during CMEs and their associated sheaths.

How to cite: Koller, F., Plaschke, F., Preisser, L., Temmer, M., and Roberts, O. W.: Solar wind conditions suppressing the production of magnetosheath jets during CME occurrence, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6521, https://doi.org/10.5194/egusphere-egu22-6521, 2022.

10:56–11:02
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EGU22-1727
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ECS
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Highlight
Oleksandr Goncharov et al.

Plasma structures with the enhanced dynamic pressure, density or speed are often observed in the Earth’s magnetosheath. These structures, known as jets and fast plasmoids, can be registered in the magnetosheath, downstream both the quasi-perpendicular and quasi-parallel bow shocks. Using measurements by the Magnetospheric Multiscale (MMS) spacecraft, Goncharov et al. (2020) showed similarities in the plasma properties of the jets and fast plasmoids. On the other hand, they pointed out that the different magnetic fields inside the structures suggest that the formation mechanisms are different. Hybrid simulations by Preisser et al. (2020) have shown differences in the mechanisms of jet and embedded plasmoid formation. Based on our comparative analysis, we discuss features of jet-like structures, their properties, occurrence, evolution, and relation to the magnetosheath parameters.

How to cite: Goncharov, O., Safrankova, J., Nemecek, Z., Xirogiannopoulou, N., Gutynska, O., Gunell, H., and Hamrin, M.: Similarities and differences of jet-like structures in different regions of the magnetosheath, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1727, https://doi.org/10.5194/egusphere-egu22-1727, 2022.

11:02–11:08
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EGU22-5337
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ECS
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Virtual presentation
Ida Svenningsson et al.

Whistler waves, right-hand polarized waves with frequencies below the electron cyclotron frequency, are common in many space plasma regions such as the Earth’s magnetosheath. They can be generated by electron temperature anisotropy, in which case the instability grows through cyclotron resonance. A common way to determine the stability of an electron distribution function is to compare the parallel and perpendicular temperature (with respect to the background magnetic field) to stability thresholds. However, such an approach based on the moments of the distribution function can potentially leave out some properties of the distribution which are important for wave generation.

In this work, we investigate the features of the electron distribution functions measured by MMS in the turbulent magnetosheath downstream of a quasi-parallel shock. We show that even though statistically whistler waves tend to occur close to the regions where the stability threshold is exceeded, they are also observed in regions predicted to be stable to wave generation. For such waves we observe that the electron pitch angle distribution often has the so-called butterfly shape (with minima in both the parallel and perpendicular directions) and is located in magnetic field minima. Using a linear numerical dispersion solver (WHAMP), we show that the butterfly distribution is unstable to whistler wave generation even though the instability threshold based on the associated moments is not exceeded. Comparison between the numerical results and waves measured by the MMS spacecraft indicate that the observed whistler waves are generated by the butterfly distribution. This phenomenon has previously been observed in mirror modes and large scale magnetic holes. Our findings show that it also occurs on smaller scales (~1 ion inertial length) in more turbulent environments, such as the quasi-parallel magnetosheath.

How to cite: Svenningsson, I., Yordanova, E., Khotyaintsev, Y., André, M., and Cozzani, G.: Kinetic generation of whistler waves in the turbulent magnetosheath, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5337, https://doi.org/10.5194/egusphere-egu22-5337, 2022.

11:08–11:18
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EGU22-3486
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solicited
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Highlight
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Virtual presentation
Stein Haaland et al.

The terrestrial magnetopause forms the boundary between the solar wind plasma with its embedded interplanetary magnetic field on one side, and the terrestrial magnetosphere, dominated by Earth's dipole field, on the other side. It is therefore a key region for the transfer of mass, momentum, and energy from the solar wind to the magnetosphere. The Cluster mission, comprising a constellation of four spacecraft flying in formation was launched more than 20 years ago to study boundaries in space. During its lifetime, Cluster has provided a wealth of new knowledge about the magnetopause. In this presentation, we give an overview of Cluster-based studies of this boundary, and highlight a selection of interesting results. 

How to cite: Haaland, S., Hasegawa, H., Paschmann, G., Sonnerup, B., and Dunlop, M.: 20 Years of Cluster Observations: The Magnetopause, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3486, https://doi.org/10.5194/egusphere-egu22-3486, 2022.

11:18–11:24
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EGU22-8347
Chao Shen et al.

Charges and electric currents source the electromagnetic field, and therefore the distribution and motions of charges determine its form. Charge separations may appear in various plasma boundary layers due to the inertia of electrons and ions or the trapping of the magnetic field. Based on the electric fields observed by MMS four spacecraft, the gradient of the electric field, as well as the charge density, can be obtained. The analysis on the electric field data acquired during dayside magnetopause crossing events by the MMS constellation shows a charge separation in the magnetopause boundary layer and that the positive charges are accumulated on the magnetospheric side while the negative charges are accumulated on the magnetosheath side. The charge separations in dayside, dawn side and dusk side magnetopause have been systematically explored. Furthermore, the spatial distribution of electric charge density in the inner magnetosphere is derived and analyzed based on the electric field measurements from September 2015 to December 2020 by MMS satellites. It is revealed that, the inner magnetosphere accumulates positive charge at dusk side and negative charge at dawn side, both of which vary with the magnetic activities. The charge and the electric field distribution confirm the presence of the Alfvén layer for the first time. In the Alfvén layer, the charge distribution has dawn-dusk asymmetry. The positive charge density at dusk is much greater than the negative charge density at dawn. These observations and analysis results could shed light on the structure of the magnetosphere and the magnetosphere-ionosphere coupling during storms.

How to cite: Shen, C., Gao, L., Zhou, Y., Ji, Y., Pu, Z., Russell, C. T., Escoubet, C. P., Bogdanova, Y. V., Zeng, G., Torbert, R., and Burch, J. L.: Charge Separations in the Geomagnetosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8347, https://doi.org/10.5194/egusphere-egu22-8347, 2022.

11:24–11:30
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EGU22-9036
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On-site presentation
Andrey Samsonov et al.

The process of charge exchange between solar wind highly charged heavy ions and exospheric neutrals produces soft X-rays in geospace. The regions with the strongest emissivity are the magnetosheath and cusps. The Soft X-ray Imager (SXI) on board the forthcoming SMILE mission will measure X-ray emissivity integrated along the line-of-sight. By analyzing 2-D maps of X-ray counts from the SXI, we can extract information about magnetopause shape and position. It has been suggested that the maximum of integrated emissivity is tangent to the magnetopause. We check this assumption using the results of MHD simulations for different points along the SMILE trajectory. We show that this method can be used for finding the magnetopause location if some corrections are applied. We present methods of determining the location of the maximum of integrated emissivity using SXI counts maps for a moderately and strongly compressed magnetosphere.

How to cite: Samsonov, A., Sembay, S., Carter, J., Branduardi-Raymont, G., and Read, A.: Using X-ray imaging to find the magnetopause location, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9036, https://doi.org/10.5194/egusphere-egu22-9036, 2022.

11:30–11:36
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EGU22-9556
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ECS
Mohammed Baraka et al.

Magnetic reconnection is a fundamental process that is ubiquitous in the universe and allows the conversion of the magnetic field energy into heating and acceleration of plasma. It’s also very important as it is responsible for the dominant transport of plasma, momentum, and energy across the magnetopause from the solar wind into the Earth magnetosphere. Coronal Mass Ejections (CMEs) and Corotating Interaction Regions (CIRs) are the primary large-scale propagating structures and important drivers of unusual space weather disturbances causing magnetospheric activity. The present study reports on a magnetic reconnection event detected by the Magnetospheric Multiscale mission (MMS) on 21 October 2015 around 04:40 UT and related to a large-scale solar wind (SW) perturbation impacting the Earth’s magnetopause. Based on OMNI data, the event impacting the Earth’s magnetosphere is ahead of weak CIR (SW beta=~7 and Alfvénic Mach number~15) where the density of solar wind is about ~20 cm -3 (compared with average SW density ~3-10 cm -3). Furthermore, the magnetosheath (MSH) density measured by MMS just after the crossing of the magnetopause is about ~95 cm -3 (compared with average MSH density ~20 cm -3). Reconnection signatures such as ion and electron jets, Hall field, and energy conversion are compared with a “classical” reconnection event observed during quiet solar wind conditions.

How to cite: Baraka, M., Le Contel, O., Canu, P., Alqeeq, S., Akhavan-Tafti, M., Retino, A., Chust, T., Alexandrova, A., and Fontaine, D. and the MMS Team: Study of a dayside magnetopause reconnection event detected by MMS and related to a large-scale solar wind perturbation., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9556, https://doi.org/10.5194/egusphere-egu22-9556, 2022.

11:36–11:42
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EGU22-11650
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ECS
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Sadie Robertson et al.

Flux ropes are twisted magnetic field structures produced during magnetic reconnection. They are thought to be important for energy transport and particle acceleration and are commonly observed throughout space plasma environments, including at the Earth’s magnetopause. Flux Transfer Events (FTEs), which typically contain flux ropes, have been observed to grow in size and flux content as they are convected over the magnetopause and into the magnetotail, contributing to flux transport in the Dungey cycle. More recently, small-scale flux ropes have been observed inside the Electron Diffusion Region (EDR) during magnetopause reconnection. 


In this study, we investigate the link between the EDR and flux ropes, presenting a survey of 245 flux ropes observed by the Magnetospheric Multiscale (MMS) mission on days during which the spacecraft also encountered the EDR. MMS measures the thermal electron and ion 3D distributions at 30 msec and 150 msec time resolution, respectively, and at spacecraft separations down to a few kilometres allowing the study of such electron-scale phenomena. We find that flux ropes are more likely to be observed closer to the EDR, and that flux ropes observed closer to the EDR tend to have greater axial magnetic field strength and therefore greater flux content. We suggest that we could be sampling a subset of flux ropes that are recently formed by the EDR and discuss how this impacts current theories for flux rope evolution on the magnetopause.

How to cite: Robertson, S., Eastwood, J., Stawarz, J., Russell, C., Giles, B., and Burch, J.: Survey of EDR-associated Magnetopause Flux Ropes with MMS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11650, https://doi.org/10.5194/egusphere-egu22-11650, 2022.

11:42–11:50
Discussion time

Fri, 27 May, 13:20–14:50

Chairpersons: Ferdinand Plaschke, Yulia Bogdanova

13:20–13:26
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EGU22-4134
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ECS
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Highlight
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On-site presentation
Konrad Steinvall et al.

Broadband waves near and below the lower-hybrid frequency have been observed at the magnetopause for a long time. In recent years NASA's multi-spacecraft mission Magnetospheric Multiscale (MMS) has enabled the waves to be analysed in much greater detail.
Previous case studies have shown that these waves can cause plasma diffusion across the magnetopause, leading to the broadening of current layers. It has also been argued that the waves might contribute to parallel electron heating and anomalous resistivity.

In this study we analyze the aforementioned waves at the magnetopause using multi-spacecraft analysis methods and data from the MMS mission. We investigate the properties of these waves on a statistical level, using several months of data. In particular, we present the relation between the waves and ambient plasma properties such as density gradients and the corresponding gradient length-scale, and to magnetic reconnection.

How to cite: Steinvall, K., Khotyaintsev, Y., and Graham, D.: Statistics of broadband low-frequency waves at the magnetopause, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4134, https://doi.org/10.5194/egusphere-egu22-4134, 2022.

13:26–13:32
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EGU22-13014
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ECS
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Highlight
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On-site presentation
Shiva Kavosi et al.

We survey one solar cycle of in situ data from the NASA THEMIS (Time History of Events and Macro scale Interactions during Substorms) and MMS (Magnetospheric Multiscale) missions to identify Kelvin–Helmholtz Instability (KHI) along Earth’s magnetopause flank. We found that KHI occurrence rates exhibit semiannual and diurnal variations; the rate maximizes at the equinoxes and minimizes at the solstices. The rate varies for different IMF By polarities; it is maximum around fall equinox for negative IMF By, while is maximum around spring equinox for positive IMF By. The rate is directly related to the dipole tilt angle. Therefore, the equinoctial hypothesis explains most part of the seasonal and diurnal variation of KHI, while the angle of the Earth's dipole in the plane perpendicular to the Earth‐Sun line explains the difference between KHI occurrence rates with positive/negative IMF By. These results reveal the key role of Sun-Earth geometry on modulating the KHI and thus the importance of Earth’s dipole tilt and Sun solar declination angle as a function of time for plasma transport across the magnetopause.

How to cite: Kavosi, S., Raeder, J., and Farrugia, C.: Seasonal and Diurnal variations of Kelvin–Helmholtz waves at Earth’s Magnetopause, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13014, https://doi.org/10.5194/egusphere-egu22-13014, 2022.

13:32–13:38
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EGU22-13170
Jean Berchem et al.

Developing an understanding of the effects of solar wind structures on the dayside magnetopause is a necessary first step for comprehending how they impact the magnetosphere.  With this aim, we have used large-scale particle-in-cell (PIC) simulations to investigate the kinetic processes occurring at the magnetopause as solar wind structures impact the dayside magnetosphere.  In this presentation, we report our progress in investigating the interaction of simple discontinuities with the magnetopause.  Our procedure is to first run a global magnetohydrodynamic (MHD) simulation to predict the overall configuration of the solar wind-magnetosphere system before the impact of the discontinuity on the magnetopause. Then, fields and plasma moments within a large sub-domain of the global MHD simulation are used to set the initial conditions of the implicit PIC simulation of the impact. Preliminary results indicate that the interactions of solar wind discontinuities with the magnetopause are very likely to generate a succession of large magnetic flux ropes that move toward the cusps. The simulations reveal the development of a strong North-South asymmetry in the twisting of the ropes. This suggests that we should expect strong North- South asymmetries in particle precipitation when such discontinuities impact the magnetopause.

How to cite: Berchem, J., Lapenta, G., Richard, R. L., Escoubet, C.-P., and Wing, S.: Large-scale PIC Simulations of the Interaction of Solar Wind Discontinuities with the Dayside Magnetopause, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13170, https://doi.org/10.5194/egusphere-egu22-13170, 2022.

13:38–13:44
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EGU22-9933
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ECS
Caoimhe Doherty et al.

The location, shape, and size of the magnetospheric polar cusps are heavily influenced by upstream solar wind conditions. The effects of dominant IMF Bz and By components on the cusp are now well known.  However, the effect of a strong IMF Bx component on the structure of the polar cusps is relatively unexplored.  We present a case study of data recorded by the four Cluster spacecraft during a crossing of the northern hemisphere high altitude cusp in the winter season of 2018, when the IMF is directed southward and sunward. The Cluster spacecraft traverse the high-altitude cusp with separations between several hundred km and 1.5 Earth radii between each spacecraft, and travel at a roughly constant latitude with changing MLT.  We study these observations in conjunction with those of the ground based SuperDARN radars.

Each spacecraft observes many flux transfer type events within the cusp, although some events are not seen on all 4 spacecraft.  The magnetic field orientation often varies significantly during each distinct passage through individual flux tubes, clearly departing from the background magnetic field direction expected in the northern hemisphere high altitude cusp. A number of these events show bidirectional electron flux signatures typical of those expected on recently reconnected open northern hemisphere flux tubes. However, some flux tubes appear to be populated only by antiparallel moving electrons, while others show an isotropic distribution of electrons and ions. The SuperDARN STO radar site observes Poleward Moving Auroral Forms (PMAFs), consistent with the interpretation that Cluster observes open flux tubes, however the directions of convecting flux tubes seen by Cluster are not always consistent with the SuperDARN picture. We consider whether the influence of the strong IMF Bx results in the relocation of the dayside reconnection site to high northern latitudes, allowing Cluster to encounter a mix of open flux tubes in the northern cusp, each of which may be connected to either the Northern or Southern polar ionosphere.  The latter configuration may be particularly supported if reconnection near the cusp results in southern hemisphere open field lines being driven anti-sunward into the northern cusp as a result of enhanced sheath flows overcoming their magnetic tension at these latitudes.

How to cite: Doherty, C., Fazakerley, A., Owen, C., Fear, R., Forsyth, C., Kavanagh, A., Trattner, K.-H., and Bogdanova, Y.: Flux Transfer Events in the Northern Hemisphere Polar Cusp Under Strong IMF Bx, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9933, https://doi.org/10.5194/egusphere-egu22-9933, 2022.

13:44–13:50
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EGU22-6554
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ECS
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On-site presentation
Simon Thor et al.

Occasionally, the auroral oval is filled with arcs pointing from the night side towards the cusp. These aurorae are known as cusp-aligned arcs. While there have been some theoretical predictions about their origins, the cause of these arcs remains unknown. For this study, we have identified both cusp-aligned arcs and regular transpolar arcs from DMSP satellite data. We investigate the correlation between the appearance of cusp-aligned arcs and various solar wind parameters, with a focus on IMF BZ and solar wind velocity. These results are then compared to the occurrence of regular transpolar arcs with respect to the same parameters. We see that cusp-aligned arcs appear almost exclusively when the IMF is northward for a long period of time, contrary to regular transpolar arcs which can have a varying, but typically northward on average, IMF. This result is in agreement with previous studies. No clear correlation between the solar wind velocity and cusp-aligned arc occurrence frequency can be seen. The results indicate that cusp-aligned arcs might be caused by Kelvin-Helmholtz instabilities at the flanks, as has been previously suggested. We also discuss other potential causes and models of cusp-aligned arcs in further detail. Additionally, we investigate the conjugacy of cusp-aligned arcs, based on DMSP data.

How to cite: Thor, S., Kullen, A., and Cai, L.: The IMF BZ Dependence of Cusp-Aligned Arcs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6554, https://doi.org/10.5194/egusphere-egu22-6554, 2022.

13:50–13:55
Laudation by ST Division President Olga Malandraki

13:55–14:05
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EGU22-901
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solicited
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Arne Richter Award for Outstanding ECS Lecture
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Virtual presentation
Chao Yue

Ion dynamics are controlled by the energy-dependent source, transport, energization, and loss processes. Systematic changes in the ion dynamics are essential to understand the ring current variations in the inner magnetosphere. The Van Allen Probes mission, which orbits near the equatorial plane inside the geosynchronous orbit, has a wide energy coverage with high energy resolution and state-of-the-art ion composition instrumentation. It provides a great opportunity to investigate plasma dynamics. In this talk, I will present some of our recent studies on the ion dynamics of different populations and species as well as the related plasma wave activity during geomagnetic quiet and active times.

How to cite: Yue, C.: Ion dynamics in the inner magnetosphere during Van Allen Probe Era, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-901, https://doi.org/10.5194/egusphere-egu22-901, 2022.

14:05–14:11
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EGU22-9917
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Highlight
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On-site presentation
Iannis Dandouras and Masatoshi Yamauchi

Outflow of ions from the terrestrial ionosphere and circulation in the magnetosphere plays an important role in the magnetospheric dynamics, by loading the magnetosphere with heavy atomic and molecular ions. Some of the outflowing ions can be re-injected into the inner magnetosphere, whereas some can completely escape to outer space. Cluster was the first mission in the magnetosphere to involve four spacecraft in a tetrahedral configuration, providing three-dimensional measurements of the space plasma parameters. The observations of the outflowing and escaping ion populations performed by Cluster are reviewed and the most prominent results highlighted. These show the dominance in the magnetotail lobes of cold plasma outflows originating from the polar caps. For the energetic heavy ion outflow the cusps constitute the main source. The dependence of the polar outflow on the solar wind parameters and on the geomagnetic activity has been evaluated for both cold ion populations and energetic heavy ions. For the later, outflow has been observed during all periods but an increase by two orders of magnitude has been shown during extreme space weather conditions. This outflow is adequate to change the composition of the atmosphere over geological time scales. At lower latitudes, the existence of a plasmaspheric wind, providing a continuous leak from plasmasphere, has been demonstrated. The general scheme of the outflowing ions circulation in the magnetosphere or escape, and its dependence on the IMF conditions, has been outlined. However, several questions remain open, waiting a future space mission to address them.

How to cite: Dandouras, I. and Yamauchi, M.: 20 Years of Cluster Observations of Heavy Ion Outflow, Circulation in the Magnetosphere and Escape: Advances and Open Questions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9917, https://doi.org/10.5194/egusphere-egu22-9917, 2022.

14:11–14:17
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EGU22-3519
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Highlight
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On-site presentation
Stein Haaland et al.

Metallic and silicate ions carry essential information about the evolution of the Earth and near-Earth small bodies. Despite this, there has so far been very little focus on ions with atomic masses higher than oxygen in the terrestrial magnetosphere. In this presentation, we report on abundances and  properties of energetic ions with masses corresponding to that of silicon (Si) and iron (Fe) in Earth's geospace.  The results are based on a newly derived data product from the Research with Adaptive Particle Imaging Detectors (RAPID) on Cluster. We find traces of both Si and Fe in all of the regions covered by the spacecraft, with the highest occurrence rates and highest intensities in the inner magnetosphere. We also find that the Fe and Si abundances are modulated by solar activity. During solar maximum, the probability of observing Fe and Si in geospace increases significantly. On the other hand, we find little or no direct correlation between geomagnetic activity and Si and Fe abundance in the magnetosphere. Both Si and Fe in the Earth's magnetosphere are inferred to be primarily of solar wind origin, as indicated by correlations with heavy ion observations from the ACE spacecraft at L1. Sputtering off the Moon is another possible source of the observed heavy ions.

How to cite: Haaland, S., Daly, P. W., Vilenius, E., and Krcelic, P.: Heavy Metal and Rock in Space: Cluster RAPID Observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3519, https://doi.org/10.5194/egusphere-egu22-3519, 2022.

14:17–14:23
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EGU22-1297
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Highlight
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On-site presentation
Masatoshi Yamauchi et al.

Molecular and metallic ions are vastly unexplored in near-Earth space because only a few terrestrial missions have been equipped with dedicated instrumentation to separate these molecular and metallic ions, within only a limited energy range (cold ions of < 50 eV and energetic ions of ~100 keV).  Nevertheless, existing data from past and on-going missions including those not designed for the required mass separation are capable of detecting many of these ions with available tools, although severe limitations exist (sensitivity and energy range in addition to mass resolution and mass range).  By combining these patchy and incomplete data, we found several features that indicate sources of these heavy ions.
(1) Combination of Kaguya and Cluster/RAPID during high flux events of solar wind heavy ions suggests that the Moon can be a substantial source for low charge-state metallic ions in the magnetosphere when the Moon is located upstream of the Earth.  This interpretation is consistent with Geotail/STICS statistics of increased flux of low charge-state heavy ions near new-Moon for medium activity (Kp=2-4).
(2) The major route of molecular ion supply (<10 keV) to the inner magnetosphere can be via low-latitude (< 60° invariant latitude, according to e-POP/IRMS) in addition to the cusp (according to Cluster/CIS and Akebono/SMS) during high outflow flux period.  This indicates extraordinary upward convection (or ion flow) at the sub-auroral region.
(3) A case study of lidar data during high flux events of solar wind heavy ions suggests that upward expansion of Na signal can be associated with molecular ion escape to the magnetosphere that is also observed by Cluster/RAPID and e-POP/IRM, although this expansion can be related to a major magnetic storm rather than solar wind event.

How to cite: Yamauchi, M., Dandouras, I., Mann, I., Haaland, S., Würz, P., Plane, J., Kastinen, D., Gunnarsdottir, T., Yau, A., Kistler, L., Hamilton, D., Christon, S., Saito, Y., Watanabe, S., and Nozawa, S.: Molecular and metalic ions in the magnetosphere: ISSI team preliminary results , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1297, https://doi.org/10.5194/egusphere-egu22-1297, 2022.

14:23–14:29
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EGU22-12276
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ECS
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Christina Toldbo et al.

The ESA Swarm mission, launched on 22 November 2013, consists of three spacecraft each equipped with a Micro Advanced Stellar Compass (μASC) designed and validated by the Technical University of Denmark (DTU). Each Star Tracker features three Camera Head Units (CHUs) orientated orthogonally to avoid simultaneous blinding. The CCD sensor inside the star tracker is sensitive to energetic particle irradiation which appear as transient bright pixels dubbed 'hot spots' on the source images.

Conventionally hot spots are removed to support nominal attitude operation, however in February and March 2018 software was uploaded to the μASCs on-board Swarm, which in addition to using the hotspot measurements to improve the star tracking is moving the measured hotspot data to the telemetry to ground. This added functionality, enables detection and monitoring of high energy particles.

In this work we present processes and analysis of the high energy radiation data obtained from the Micro Advanced Stellar Compass (μASC) on board ESA's Swarm mission, from February 2018 to end of 2021. Taking advantage of three years of data, high sample rates (1-2 Hz), the beneficial orientation of the camera heads and simultaneous measurements from all three spacecraft it is possible to determine spatial and temporal derivatives of the electric and magnetic fields. Furthermore, since the Swarm spacecraft are in near-polar orbits at an altitude of 450-510 km above Earth's surface the spacecraft continuously monitor and map high energy particles at the South Atlantic Anomaly (SAA) of relevance for future mission planning as well as provide detailed time-radiation relations from charge injection processes from e.g. CMEs.

How to cite: Toldbo, C., Herceg, M., Denver, T., Sushkova, J., Benn, M., Jørgensen, P. S., and Jørgensen, J. L.: Mapping High Energy Particle Population in Earth's Magnetosphere Using Augmented Star Trackers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12276, https://doi.org/10.5194/egusphere-egu22-12276, 2022.

14:29–14:35
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EGU22-9693
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Highlight
Romain Maggiolo et al.

The protective effect of a planetary magnetic field on the planet’s atmosphere is still debated. This study focuses on a particular aspect of the chain of processes leading to atmospheric escape: the energy transfer from the solar wind to the upper atmosphere. Magnetized planets are surrounded by a large-scale magnetosphere which has two opposite effects. On the one hand, it efficiently diverts the solar wind so that only a small fraction of the solar wind energy flux that intercepts it eventually ends up being dissipated in the upper atmosphere. On the other hand, a large-scale magnetosphere dramatically increases the area of interaction between the solar wind and the planet and thus the amount of solar wind energy that may potentially be funneled into its upper atmosphere.

In this study, we estimate the solar wind energy flux currently dissipated in the Earth’s upper atmosphere using empirical formulas derived from observations found in the literature. We compare it to the solar wind energy that would intercept the induced magnetosphere of a hypothetical unmagnetized Earth. We show that the solar wind energy dissipated in the upper atmosphere is comparable to -if not higher than- the solar wind energy that would intercept a hypothetical unmagnetized Earth. This result indicates that the Earth's large-scale magnetic field does not protect the Earth’s upper atmosphere but rather increases the solar wind energy deposition.

How to cite: Maggiolo, R., Maes, L., Cessateur, G., Darrouzet, F., De Keyser, J., and Gunell, H.: How does the presence of a large-scale magnetic field impact the solar wind energy dissipation in the Earth’s upper atmosphere?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9693, https://doi.org/10.5194/egusphere-egu22-9693, 2022.

14:35–14:41
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EGU22-1800
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ECS
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Highlight
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On-site presentation
Amy Fleetham et al.

The Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) has revolutionized the way in which we can study the electrical current systems present over the poles of Earth. With high cadence measurements taken in both hemispheres, the data has proven invaluable in developing our understanding of the current systems that couple the magnetosphere and ionosphere and how they change in response to space weather. By employing the AMPERE data set, we aim to offer new insights into the complex and dynamic region 1 and region 2 current systems as they respond to the impact of solar wind disturbances on the magnetosphere and the driving of geomagnetic storms.

We investigate the relationship between the hemispherically-integrated current flowing into or out of each pole and upstream solar wind parameters to understand how these currents are driven.  As expected, current magnitude increases with increasing interplanetary magnetic field strength and solar wind speed.  A key aim of the analysis is to determine if current magnitude saturates under strongly driven conditions, in the same way that the cross-polar cap potential is known to saturate.  We present preliminary results, indicating a variety of behaviours at high driving, and discuss these in terms of theories of solar wind-magnetosphere coupling.

How to cite: Fleetham, A., Milan, S., Imber, S., and Anderson, B.: AMPERE and The Electric Current of the Geomagnetic Storm, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1800, https://doi.org/10.5194/egusphere-egu22-1800, 2022.

14:41–14:50
Discussion time

Fri, 27 May, 15:10–16:40

Chairpersons: C.-Philippe Escoubet, Yulia Bogdanova

15:10–15:16
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EGU22-6366
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ECS
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Highlight
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Virtual presentation
Nithin Sivadas et al.

The polar cap potential, a measure of the magnetosphere's response to the solar wind, levels off during high solar wind electric field values. Several explanations have been proposed for this saturation effect, but there has been no consensus. We show that the saturation may merely be a perception created by uncertainty in the solar wind measurements and its propagation to the polar cap. Correcting this uncertainty reveals a true response that is linear across the full range of the solar wind electric field values. These findings indicate that extreme space weather events can elicit a larger impact on Earth than we'd expect if the polar cap potential were to saturate.

How to cite: Sivadas, N., Sibeck, D., Subramanyan, V., Walach, M.-T., Murphy, K., and Halford, A.: Uncertainty in solar wind propagation may explain polar cap potential saturation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6366, https://doi.org/10.5194/egusphere-egu22-6366, 2022.

15:16–15:22
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EGU22-4018
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ECS
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On-site presentation
Leonard Schulz et al.

The strong growth of the space sector along with the use of smaller satellites, for example Cubesats, has fueled the rising implementation of satellite constellations. Not only in commercial spaceflight small satellite constellations are used frequently - there also have been ideas put forward for scientific missions using constellations exceeding the 4 spacecraft constellations previously used for in-situ multi-point measurements in space plasma physics (e.g. CLUSTER or MMS). Thus, there is a need to expand current analysis techniques of those multi-point measurements to more than 4 spacecraft and characterize the benefits of a larger number of satellites. Such an analysis technique is the wave telescope, e.g. introduced in Motschmann et al., 1996. The wave telescope allows to use e.g. magnetic field data from different points in space (the different spacecraft) to estimate a spatial fourier transform and with that is able to detect multiple waves. Thus, using a confined time interval, the frequency and wave vector of several different waves can be detected with high precision. Since its introduction, the wave telescope has been successfully applied for detection of waves in in-situ magnetic field data from Earth's magnetospheric environment. Using artificial data of magnetic plane waves in simulations, we revisit the limitations of the wave telescope for satellite numbers of 4 or less and explore the quality of detection for satellite configurations of 5 and more spacecraft. We present structured analysis of the spatial analysis limit from 1D upwards, named the nyquist wavenumber or wave vector (analogous to the nyquist frequency in the frequency domain). Additionally, we show that the wave telescope suffers from so called spatial blindness when the chosen satellite configuration is not moving and non-random phase plane waves at the same frequency are present. This blindness reduces the possible number of waves detected to no more than one.

How to cite: Schulz, L., Glassmeier, K.-H., Plaschke, F., and Motschmann, U.: Revisiting the wave telescope for larger numbers of spacecraft, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4018, https://doi.org/10.5194/egusphere-egu22-4018, 2022.

15:22–15:28
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EGU22-2347
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On-site presentation
Yasuhito Narita et al.

Finding a set of model parameters using the in-situ spacecraft data (such as in the Earth or planetary magnetospheres and in the solar wind) is one of the common exercises in the field of space physics. Above all, parameter estimation using Capon's minimum variance projection, originally developed in the field of array seismology, has successfully been applied to recognizing various structures or spatial patterns in space. Examples of the Capon method can be found in the analysis of the wave structures (plane waves, spherical waves, and phase-shifted waves) and the static, large scale structures (planetary dipolar field and higher-order fields). In order to extend the scientific potential of array magnetic field data such as the Cluster, THEMIS, and MMS missions, the performance and the limits of Capon's method are studied in detail using both analytical and numerical approaches. Our findings are: 1) Capon's method is a simple yet robust implementation of the maximum likelihood method, and 2) its accuracy or error can be evaluated analytically. It is suggested that other inversion techniques such as the least square fitting, the singular value decomposition, the Tikhonov regularization, and the eigenvector-based method may be as competitive as Capon's method when the statistical method is limited in the data analysis. Data analysts have thus a wider range of choices for the structure recognition using array data. 

How to cite: Narita, Y., Toepfer, S., Glassmeier, K.-H., and Motschmann, U.: Parameter estimation using Cluster array magnetic field data: perfomance and limits of Capon's method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2347, https://doi.org/10.5194/egusphere-egu22-2347, 2022.

15:28–15:34
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EGU22-8445
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ECS
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On-site presentation
Kristin Pump et al.

Mercury is the smallest an innermost planet of our solar system and has a dipole-dominated internal magnetic field that is relatively weak, very axisymmetric and significantly offset towards north. Through the interaction with the solar wind, this field leads to a magnetosphere. Compared to the magnetosphere of Earth, Mercury’s magnetosphere is smaller and more dynamic. To understand the magnetospheric structures and processes we use in-situ MESSENGER data to develop a semi-empiric model, which can explain the observations and help to improve the mission planning for the BepiColombo mission en-route to Mercury.

We will present this semi-empiric KTH-model, a modular model to calculate the magnetic field inside the Hermean magnetosphere. Korth et al. (2015 and 2017) published a model, which is the basis for the KTH-Model. In this new version, the calculation of the magnetic field for the neutral current sheet is restructured based on observations rather than ad-hoc assumptions so that the description is more realistic. Furthermore, a new model is added to depict the partial ring current. An analysis of the residuals shows a better visibility of the field-aligned currents. In addition, this model offers the possibility to improve the main field determination.

How to cite: Pump, K., Heyner, D., and Plaschke, F.: Revised Modular Model of Mercury’s Magnetospheric Magnetic Field, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8445, https://doi.org/10.5194/egusphere-egu22-8445, 2022.

15:34–15:40
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EGU22-2575
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ECS
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On-site presentation
Simon Töpfer et al.

Poloidal–toroidal magnetic field decomposition is a useful application of the Mie representation for the reconstruction of Mercury‘s internal magnetic field. In addition, the decomposition method enables us to determine the current density observationally and unambiguously in the local region of magnetic field measurement. The application and the limits of the decomposition method are tested against the Mercury magnetic field simulation in view of BepiColombo‘s arrival at Mercury in 2025. The simulated magnetic field data are evaluated along the planned Mercury Planetary Orbiter (MPO) trajectories and the current system that is crossed by the spacecraft is extracted from the magnetic field measurements. Afterwards, the resulting currents are classified in terms of the established current system in the vicinity of Mercury.

 

Reference

  • Toepfer, S., Narita, Y., Exner, W., Heyner, D., Kolhey, P., Glassmeier, K. ‐H., Motschmann, U. (2021c)  The Mie representation for Mercury’s magnetospheric currents, Earth, Planets and Space 73:204. https://doi.org/10.1186/s40623-021-01536-8
  • Toepfer, S., Narita, Y., Glassmeier, K.-H., Heyner, D., Kolhey, P., Motschmann, U., Langlais, B. (2021a) The Mie representation for Mercury’s magnetic field, Earth Planets Space 73:65. https://doi.org/10.1186/s40623-021-01386-4

 

 

How to cite: Töpfer, S., Narita, Y., Heyner, D., Kolhey, P., Glassmeier, K.-H., and Motschmann, U.: The Mie representation for Mercury‘s magnetospheric currents, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2575, https://doi.org/10.5194/egusphere-egu22-2575, 2022.

15:40–15:46
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EGU22-9532
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ECS
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On-site presentation
Soboh Alqeeq et al.

In the present work, we consider 49 dipolarization fronts (DF) detected by the Magnetospheric Multiscale (MMS) mission on 2017, near the Earth’s magnetotail equator (Bx<5nT). Criteria for selecting DF using an AIDApy routine are based on difference of maximum and minimum values computed with a 306 s sliding window. They request a Bz increase, an ion velocity increase and a density decrease. This first automatic selection is then ajusted manually with the following criteria : Bz increase larger than 5 nT, ion velocity larger than 150 km/s, density decrease and both ion and electron temperature increases. All these events belong to the most common category (A) defined by Schmid et al., 2015 in term of density decrease and temperature increase at the DF. However, based on a superposed epoch analysis of DF basic properties (magnetic field, density, velocity, ...) we distinguish two subcategories of events depending on the shape of the DF. The first subcategory (55.1%) corresponds to a slow decrease of the magnetic field after the DF and is associated with smaller ion velocity and hotter plasma. The second subcategory (44.9%) has the same time scale for the rising and the falling of the magnetic field (a bump) associated with a decrease of ion and electron pressures and faster velocity as shown in Alqeeq et al. 2021. For both categories we found that ions are mostly decoupled from the magnetic field by the Hall fields. The electron pressure gradient term is also contributing to the ion decoupling and likely responsible for an electron decoupling at DF. We also analyzed the energy conversion process. For the first subcategory we found that the energy in the spacecraft frame is transferred from the electromagnetic field to the plasma (J·E>0) ahead or at the DF. For the second subcategory, we found the same behavior ahead or at the DF whereas it is the opposite (J·E<0) behind the front. In the fluid frame, we found that the energy is mostly transferred from the plasma to the electromagnetic field (J·E ′ <0) ahead or at the DF for both subcategories but energy dissipation (J·E ′ >0) only occurs behind the front for the second subcategory. The possible origin of these two subcategories is discussed.

How to cite: Alqeeq, S., Le Contel, O., Canu, P., Retinò, A., Breuillard, H., Chust, T., Alexandrova, A., Mirioni, L., Khotyaintsev, Y., Nakamura, R., Wilder, F., Wei, H., Fischer, D., Gershman, D., Burch, J., Torbert, R., Giles, B., Fuselier, S., Ergun, R., and Lindqvist, P. A. and the MMS Team: A statistical study of dipolarization fronts observed by MMS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9532, https://doi.org/10.5194/egusphere-egu22-9532, 2022.

15:46–15:52
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EGU22-3297
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Highlight
Rumi Nakamura et al.

Using data from fleet of spacecraft in the near-Earth night-side magnetosphere, we study the three-dimensional evolution of the magnetotail current sheet following the expansion phase onset of a moderate substorm (AL ~-450 nT) after 09:10 UT, April 10, 2020.  Magnetotail disturbances are observed by GOES 17 and Cluster in the midnight region.  During this substorm the BepiColombo spacecraft traversed the premidnight region duskward at 9-11 RE downtail during its Earth Flyby.  The four Cluster satellites, which were separated mainly in north-south direction, crossed the inner magnetosphere successively from north to south. They enable us to monitor the vertical (latitudinal) structure and the sequential changes of the magnetotail current sheet until the end of the recovery phase of the substorm, around 11 UT.  Multiple dipolarizations and multiple transient field-aligned currents (FAC) were observed by Cluster.  The first dipolarization around the onset, which was detected by GOES 17 in the geosychronous region, was accompanied by a plasma sheet expansion observed by the two leading Cluster 3 and 4 satellites. BepiColombo in the premidnight region observed continuous thinning of the current sheet, a typical signature of the growth phase, accompanied by a couple of transient magnetic signatures indicating flux rope and/or TCR formation around the onset.  Cluster 1 detected the most intense FAC associated with the dipolarization event starting around 10 UT, when the two BepiColombo MPO and MIO spacecraft observed dipolarization and energetic particle injection. These observations indicate the duskward and tailward expansion in the course of multiple dipolarizations.  Using the unique dataset from the multi-point observations, we examine the structure of the large-scale current sheet and analyze the embedded transient intense field-aligned current disturbances. By also comparing with an empirical magnetic field model, we obtain the changes of the near-Earth magnetotail structure during the multiple dipolarization event.

How to cite: Nakamura, R., Slavin, J., Schmid, D., and Sun, W. and the The April 10, 2020 BepiColombo Earthflyby Substorm Study Team: Azimuthal and latitudinal changes of the near-Earth magnetotail current sheet structure during multiple dipolarizations of a substorm, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3297, https://doi.org/10.5194/egusphere-egu22-3297, 2022.

15:52–15:58
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EGU22-4579
Daniil Korovinskiy et al.

The compressible electron magnetohydrodynamics (EMHD) Grad–Shafranov (GS) reconstruction technique is applied to recover a magnetic reconnection electron diffusion region (EDR) immersed in a flux‐rope type dipolarization front observed by the Magnetospheric Multiscale (MMS) mission on 8 September 2018 at nearly 14:51:30 UT. An event was reported in the study of Marshall et al. (JGR, 2020). EMHD GS reconstruction confirms mainly the results of the cited study. Particularly, MMS1 is found to cross the very center of EDR at the initial steady-state stage. The reconstruction results allow also the suggestion that the reported X-line and EDR were not single ones, but rather the chain of X-lines (two at least) separated in north-south direction for about 10 de could exist.

How to cite: Korovinskiy, D., Panov, E., Nakamura, R., and Hosner, M.: EMHD Grad–Shafranov reconstruction of the electron diffusion region within a flux rope, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4579, https://doi.org/10.5194/egusphere-egu22-4579, 2022.

15:58–16:04
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EGU22-5853
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ECS
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On-site presentation
Martin Hosner et al.

The Dipolarization Front (DF), which is a sharp increase of the northward magnetic field component, accompanied by fast earthward-moving plasma flows, is a well known phenomenon in the Earth's Magnetotail. Plasma characteristics also change at the front, from colder and denser ahead of the front to a hotter and more diluted plasma at the trailing side. The DF is therefore considered to be the boundary between ambient plasma and the hotter reconnection outflow jets. The DF can be the host of several energy conversion processes between plasma particles and waves e.g. due to various instabilities. A recent statistical study by Hosner et al. PoP 2022 showed that all of the studied DFs are accompanied by enhanced wave activity around the lower hybrid frequency, suggesting the high occurrence of the Lower-Hybrid Drift instability (LHDI) at DFs. In the present study we investigate the evolution of the energy conversion process in a flux rope type DF, for which an electron-diffusion region was reported (Marshall et al. JGR 2020). We first examine the wave characteristics and LHDI signatures to compare and to contrast flux rope and non-flux rope type DFs. Secondly, we apply a magnetic field reconstruction technique (Denton et al. JGR 2020) to this event using MMS data, to reconstruct the changes of the local magnetic field structures of the flux rope and temporal/spatial evolution of the energy conversion processes within the DF.

How to cite: Hosner, M., Nakamura, R., Schmid, D., Nakamura, T., Panov, E., and Korovinskiy, D.: Investigation of the evolution of energy conversion processes at an EDR-accompanied dipolarization front, using polynomial magnetic field reconstruction techniques, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5853, https://doi.org/10.5194/egusphere-egu22-5853, 2022.

16:04–16:10
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EGU22-1976
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Highlight
Evgeny V. Panov et al.

By combining three-probe THEMIS observations and 3-D Particle-in-Cell simulations, we identify key structures on the ion gyroradius scale that occur in connection with ballooning-interchange instability (BICI) heads in the Earth’s magnetotail. The mesoscale structures occur at sites of strong ion velocity shear and vorticity where the thermal ion Larmor radius is about half of the width of the head. Finer structures occur at the smaller scales characterizing the wavelength of the electromagnetic ion cyclotron waves generated at the heads. These two processes act to erode and thin the current sheet, thereby forming a local magnetotail configuration that is favorable for reconnection.

How to cite: Panov, E. V., Lu, S., and Pritchett, P. L.: Magnetotail Ion Structuring by Kinetic Ballooning-Interchange Instability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1976, https://doi.org/10.5194/egusphere-egu22-1976, 2022.

16:10–16:16
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EGU22-4045
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ECS
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Virtual presentation
Louis Richard et al.

We investigate a series of Earthward bursty bulk flows (BBFs) observed by the Magnetospheric Multiscale (MMS) spacecraft in the Earth’s magnetotail (X ~ -24 Re, Y ~ 7 Re, Z ~ 4 Re). At the leading edges of the BBFs, we observe complex magnetic field structures. In particular, we focus on one which presents a chain of small scale (~0.5 Re) dipolarizations, and another with a large scale (~3.5 Re) dipolarization. Although the two structures have different scales, both of these structures are associated with flux increases of supra-thermal ions (Ki > 100 keV). We investigate the ion acceleration mechanism and its dependence on the mass and charge state. We show that the ions with gyroradii smaller than the scale of the structure are accelerated by the ion bulk flow. We show that whereas in the small-scale structure, ions with gyroradii comparable with the scale of the structure undergo resonance acceleration, the acceleration in the larger-scale structure is more likely due to a spatially limited electric field. In both cases, we discuss the adiabaticity of the acceleration mechanism.

How to cite: Richard, L., Khotyaintsev, Y. V., Graham, D. B., Vaivads, A., Nikoukar, R., Cohen, I. J., Turner, D. L., Fuselier, S. A., Russell, C. T., Giles, B. L., and Lindqvist, P.-A.: Ion Acceleration at Magnetotail Turbulent Plasma Jet Fronts, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4045, https://doi.org/10.5194/egusphere-egu22-4045, 2022.

16:16–16:22
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EGU22-6459
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ECS
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Highlight
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Virtual presentation
Pavel Shustov et al.

The near-Earth electron population is largely formed by earthward electron transport from the middle and distant magnetotail. Such transport is associated by electron adiabatic heating by the convection electric field. Although the adiabatic heating models predict formation of strongly anisotropic electron populations, spacecraft observations show that hot electrons are well isotropic in the near-Earth magnetotail. One of the possible isotropisation mechanisms is the electron scattering by magnetic field line curvature in the magnetotail current sheet with the stretched magnetic field line configuration.  In this presentation we show model results of electron transport and curvature scattering for slow magnetosphere convection. Our model combines the canonical theory of the electron guiding center motion and the mapping technique of electron pitch-angle scattering. We show formation of electron spectra typical for the near-Earth magnetotail and estimate the contribution of the curvature scattering to electron losses.

How to cite: Shustov, P., Artemyev, A., and Petrukovich, A.: Electron earthward transport in the Earth magnetotail: adiabatic convection heating and magnetic curvature scattering, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6459, https://doi.org/10.5194/egusphere-egu22-6459, 2022.

16:22–16:28
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EGU22-9481
Olivier Le Contel et al.

In July 2017, the MMS constellation was evolving in the magnetotail with an apogee of 25 Earth radii and an average inter-satellite distance of 10 km (i.e. at electron scales). On 23rd of July around 16:19 UT, MMS was located at the edge of the current sheet which was in a quasi-static state. Then, MMS suddenly entered in the central plasma sheet and detected the local onset of a small substorm as indicated by the AE index (~400 nT). Fast plasma flows towards the Earth were measured for about 1 hour starting with a period of quasi-steady flow and followed by a series of saw-tooth plasma jets (“bursty bulk flows”). In the present study, we focus on a short sequence related to the crossing of an ion scale current sheet embedded in a fast earthward flow. The current sheet appears to be corrugated and with a significant guide field (BL/BM~0.5). Tailward propagating electrostatic solitary waves are detected just after the magnetic equator crossing and at the edge of the current sheet. We also analyze in detail an electron vortex magnetic hole also detected at the edge of this current sheet and discuss the Ohm’s law and energy conversion processes. We find that the energy dissipation associated with the electron vortex is three times greater (0.15nW/m3) than at the current sheet crossing (0.05nW/m3). Based on estimated statistical weight of these vortices we discuss possible consequences for the energy dissipation associated with fast earthward plasma flows.

How to cite: Le Contel, O., Retino, A., Alexandrova, A., Nakamura, R., Alqeeq, S., Baraka, M., Chust, T., Mirioni, L., Catapano, F., Jacquey, C., Toledo-Redondo, S., Stawarz, J., Goodrich, K., Gershman, D., Fuselier, S., Mukherjee, J., Ahmadi, N., Graham, D., Argall, M. R., and Fischer, D. and the A MMS Team: Multiscale analysis of a current sheet crossing associated with a fast earthward flow during a substorm event detected by MMS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9481, https://doi.org/10.5194/egusphere-egu22-9481, 2022.

16:28–16:40
Discussion time