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.

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.

We calculate the change in electron kinetic entropy, ΔS_e, 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, ΔT_e, and the upstream plasma beta. Shocks with a small upstream plasma beta have a large ΔS_e while shocks with high upstream plasma beta have a small ΔS_e.

The calculated changes in kinetic entropy, density and temperature are used to estimate the proxy adiabatic index, γ_e, 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 B_Z 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 d_e 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.

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.

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.

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.

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.

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 23^rd 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.