Collisionless shocks are ubiquitous in the universe as they are found in different astrophysical environments, from planets to galaxy clusters. Extensive effort has been put into understanding their rich dynamics and their effects on the surrounding environments, such as the generation of foreshocks, turbulent sheaths and characteristic transient phenomena.
Heliospheric shocks are the only ones that are directly accessible by in-situ measurements. Missions, such as Solar Orbiter, STEREO and Parker Solar Probe have deepened our knowledge of interplanetary shocks and the associated regions, while MMS, Cluster, THEMIS, Cassini, Maven and others have done the same for the planetary bow shocks.
Furthermore, thanks to high-performance computing, global and local simulations have played a vital role in resolving major gaps in our knowledge of collisionless shocks.
Despite these efforts, many questions remain open. In particular, we still do not fully understand the mechanisms associated with certain aspects of particle heating and acceleration, wave generation, wave-particle interaction and energy redistribution at shocks.
Additionally, details about how transient structures, such as hot flow anomalies, foreshock bubbles, cavitons, spontaneous hot flow anomalies, magnetosheath jets etc. are formed and how they interact with and impact the near-Earth environment are also largely still unknown. We thus welcome observational, numerical, and theoretical works focusing on the study of plasma processes at collisionless shocks and surrounding regions.
Orals:
Tue, 16 Apr
| Room 0.16
Chairpersons: Ahmad Lalti, Adrian LaMoury, Savvas Raptis
We briefly summarize some of the latest, impactful results concerning the nature and physics of collisionless shock waves as observed by NASA’s Magnetospheric Multiscale (MMS) mission. MMS routinely observes Earth’s bow shock and also infrequently captures interplanetary shocks at 1 AU. With the four, identical observatories outfitted with a comprehensive payload of state-of-the-art plasma instrumentation, MMS offers unprecedented capabilities for studying the micro-to-global-scale nature of shocks in near-Earth space. New results highlighted include: the global energy budget and energy partitioning at Earth’s bow shock; complexity and significance of the quasi-parallel shock regime and the ion foreshock; the acceleration of ions to >1 MeV and electrons to relativistic (>100 keV) energies; and kinetic-scale dynamics of shock fronts including reconnection and We finish with new results of an ongoing large-scale, statistical study of Earth’s bow shock empowered by machine learning applied to the full MMS dataset. We finish with a discussion of the upcoming MMS orbital configurations in regards of new studies plus idealized concepts for future missions to study collisionless shocks.
How to cite:
Turner, D.: Insights on collisionless shock physics from the Magnetospheric Multiscale (MMS) mission at Earth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13539, https://doi.org/10.5194/egusphere-egu24-13539, 2024.
Collisionless shocks are efficient particle accelerators. While ion acceleration by shocks has been intensively studied using spacecraft data and numerical models, the main focus has been on the case of a steady upstream. In the steady upstream case, it has been shown that quasi-parallel shocks are much more efficient ion accelerators than quasi-perpendicular shocks. However, the solar wind is in general highly dynamic, containing current sheets which correspond to a magnetic shear. In this study we use a local 2.5D hybrid particle-in-cell (particle ions, fluid electrons) model to study how the ion acceleration of quasi-perpendicular shocks is affected when the upstream contains highly sheared tangential discontinuities. We show that, even in the absence of foreshock transients, the current sheets can cause a significant increase in the flux of high-energy ions. The acceleration can be explained by the following simple model. When the upstream TD is close to the shock, the shock-reflected ions can cross it during the upstream part of their gyro–motion. After crossing the TD, the large magnetic shear, corresponding to a sign change of the magnetic field direction, results in a meandering ion trajectory. This motion takes the ion further upstream, where it is further energized by the upstream convection electric field. The net effect of this process is a local ion acceleration efficiency of a few %, as quantified as the fraction of energy (in the downstream and in the downstream frame) that is carried by ions with energies larger than 10 times the upstream bulk kinetic energy. This is comparable to the efficiency of quasi-parallel shocks in the case of a steady upstream. Such discontinuities can therefore be an important source of energetic ions at quasi-perpendicular shocks, even if no foreshock transient is formed.
How to cite:
Steinvall, K. and Gingell, I.: Ion acceleration due to highly sheared tangential discontinuities at quasi-perpendicular shocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7538, https://doi.org/10.5194/egusphere-egu24-7538, 2024.
Ida Svenningsson, Emiliya Yordanova, Yuri V. Khotyaintsev, Mats André, and Giulia Cozzani
Whistler waves are found in various space plasma environments, such as the Earth’s magnetosheath, where they affect particle dynamics and energy transfer. Through wave-particle interactions, they contribute to changes in both the energy and pitch angle of electrons. However, the significance of whistler waves in different plasma regions is not fully known.
In this work, we use MMS measurements to calculate the occurrence and properties of whistler waves in the Earth’s magnetosheath. Based on selected MMS orbits, we compare the plasma conditions offered by the more stationary quasi-perpendicular (Q⊥) to the more fluctuating quasi-parallel (Q॥) magnetosheath. We show that the whistler waves occur in local magnetic dips and density peaks and are not necessarily correlated with electron temperature anisotropy. Also, there is an elevated occurrence downstream of Q⊥ shocks, compared to the Q॥ configuration. Further, by calculating pitch-angle diffusion coefficients, we find that whistler waves can significantly reshape the electron velocity distribution during the time a plasma parcel spends in the magnetosheath, which has important implications for the plasma dynamics of the magnetosheath region.
How to cite:
Svenningsson, I., Yordanova, E., Khotyaintsev, Y. V., André, M., and Cozzani, G.: Electron velocity-space scattering from whistler waves in the Earth’s magnetosheath, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16963, https://doi.org/10.5194/egusphere-egu24-16963, 2024.
Dynamic pressure variations that are upstream from the magnetopause can interact with the coupled magnetospheric and ionospheric system, causing significant auroral responses, which indicates magnetospheric compressions, wave propagations and disturbances of current system. Recent studies have shown that not only large-scale solar wind structures but also locally-generated foreshock transients can be associated with strong dynamic pressure variations and further induce such auroral responses. However, how these auroral responses evolve in 2D perspective and how the corresponding current system and electron precipitation evolve in 2D perspective are still unclear. Thus, in our study, we used the coordinated observations between THEMIS probes and the ground-based all-sky images at South Pole to statistically investigate the 2D evolution of discrete and diffuse auroral responses to both solar wind structures and foreshock activities. The discrete auroral evolution shows that the dynamic pressure variations upstream from the magnetopause can induce upward field-aligned currents near the magnetopause in the magnetosphere. These currents can extend earthward and most of them extend duskward, causing the bifurcation of auroral oval. The diffuse auroral patterns reveal that in the ionosphere, the area with compression-related electron precipitations propagates poleward. The azimuthal motion of compression-related electron precipitations can be either dawnward or duskward, depending on the azimuthal propagation of the magnetospheric compressions. We further found that the location, size and associated dynamic pressure change of the upstream solar-wind or foreshock transients can modify the shape and 2D evolution of the corresponding auroral patterns.
How to cite:
Wang, B. and Xu, X.: The 2D evolution of the M-I responses to solar wind/foreshock transients based on the coordinated observation between THEMIS and ground-based ASI, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5084, https://doi.org/10.5194/egusphere-egu24-5084, 2024.
Yufei Zhou, Savvas Raptis, Shan Wang, Chao Shen, Nian Ren, and Lan Ma
The study of jets downstream of Earth's bow shock has been a subject of extensive investigation for over a decade due to their close connection with shock dynamics and their profound impact on the geomagnetic environment. While the variability of the solar wind and its interaction with Earth's magnetosphere provide valuable insights into jets across a range of parameters, a broader parameter space can be explored by examining the downstream of other planetary bow shocks. Here we report the existence of anti-sunward and sunward jets downstream of Jovian bow shock and show their close association to magnetic discontinuities. The anti-sunward jets are possibly generated by a shock--discontinuity interaction. Finally, through a comparative analysis of jets observed at Earth, Mars, and Jupiter, we show that the size of jets scales with the size of bow shock.
How to cite:
Zhou, Y., Raptis, S., Wang, S., Shen, C., Ren, N., and Ma, L.: Magnetosheath jets at jupiter and across the solar system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3342, https://doi.org/10.5194/egusphere-egu24-3342, 2024.
Florian Koller, Cyril Simon Wedlund, Manuela Temmer, Ferdinand Plaschke, Luis Preisser, Zoltan Vörös, Owen Wyn Roberts, Adrian Pöppelwerth, Savvas Raptis, and Tomas Karlsson
The plasma properties of the incoming solar wind undergo significant changes as they cross the terrestrial bow shock and traverse the magnetosheath. The solar wind itself can be categorized into different categories depending on their solar origin and linked to large-scale structures like coronal mass ejections (CMEs) or stream interaction regions (SIRs) detected in near-Earth space. Using measurements from THEMIS combined with OMNI data spanning from 2008 onward, we provide a statistical overview of temperature anisotropy-driven plasma instabilities in the dayside magnetosheath. This analysis is conducted under various upstream solar wind conditions and structures, which significantly impact the plasma environment in the magnetosheath. We extend this analysis to transient phenomena such as dynamic pressure enhancements in the magnetosheath (so-called jets) as well.
As a consequence of collisionless shock physics, the shocked plasma is expected to display vastly different behaviours in terms of plasma properties and stability when sorted into quasi-parallel and quasi-perpendicular downstream magnetosheath regions. However, this categorization is complicated by the presence of fast solar wind streams originating in solar coronal holes due to the significantly increased ion energy flux of the plasma. Consequently, in our statistical analysis, we emphasize the importance of magnetosheath classification under different solar wind plasma origins and show how stable the magnetosheath plasma is in any given upstream solar wind condition. Combining knowledge of solar wind origins and structures with shock and magnetosheath research can contribute to an improved classification of quasi-perpendicular and quasi-parallel shock conditions across all solar wind origins.
How to cite:
Koller, F., Simon Wedlund, C., Temmer, M., Plaschke, F., Preisser, L., Vörös, Z., Roberts, O. W., Pöppelwerth, A., Raptis, S., and Karlsson, T.: Solar Wind Structures Impacting the Plasma Stability and Ion Energy Distribution Downstream of the Terrestrial Bow Shock, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12210, https://doi.org/10.5194/egusphere-egu24-12210, 2024.
Adrian Pöppelwerth, Georg Glebe, Johannes Z. D. Mieth, Florian Koller, Tomas Karlsson, Zoltan Vörös, and Ferdinand Plaschke
Transient enhancements in the dynamic pressure, so-called magnetosheath jets or simply jets, are abundant in the magnetosheath. They propagate from the bow shock towards the magnetopause. On their way through the magnetosheath, jets interact with the ambient plasma. The scale size of jets is determined almost exclusively with statistical studies, but not for individual jet events. We use multipoint measurements from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission to study the passage of a single jet and obtain its size. We observe an evasive motion of the plasma on the jet path. Using this flow pattern we can reconstruct the position of the central axis of this jet along its propagation direction. This allows us to estimate the spatial distribution of the dynamic pressure within the jet. Furthermore, the size perpendicular to the propagation direction can be estimated for different cross sections. Using this method, the scale size of individual jet events can be determined with multiple spacecraft. In principle, only two spacecraft are needed if we assume a simplified geometry. In the case we investigated, both the dynamic pressure and the perpendicular size increase along the propagation axis from the front part towards the center of the jet and decrease again towards the rear part.
How to cite:
Pöppelwerth, A., Glebe, G., Mieth, J. Z. D., Koller, F., Karlsson, T., Vörös, Z., and Plaschke, F.: Scale Size Estimation of Magnetosheath Jets, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5564, https://doi.org/10.5194/egusphere-egu24-5564, 2024.
Jonas Suni, Minna Palmroth, Lucile Turc, Markus Battarbee, Yann Pfau-Kempf, Maxime Dubart, Urs Ganse, Leo Kotipalo, Vertti Tarvus, and Abiyot Workayehu
When plasma and magnetic field discontinuities in the solar wind interact with Earth’s magnetic field, they can significantly alter the properties and dynamics of Earth’s bow shock, magnetosheath, and magnetopause. In this study, we investigate magnetosheath dynamic pressure enhancements generated by the interaction between a solar wind rotational discontinuity with Earth’s bow shock in a 2D simulation run of the global magnetospheric hybrid-Vlasov model Vlasiator. We find that as the discontinuity is advected into the bow shock, several fast-mode pulses associated with enhanced dynamic pressure are launched toward the Earth. In addition, the interaction between discontinuity and shock generates transient enhancements of dynamic pressure at the bow shock that move Earthward together with the discontinuity. We find that the fast-mode pulses are able to traverse the magnetosheath and disturb the magnetopause. This finding differs from the results of previous studies using 2D and 3D MHD simulations as well as spacecraft measurements, which concluded that magnetopause disturbances should be caused by the rotational discontinuity itself and the dynamic pressure enhancement associated with it.
How to cite:
Suni, J., Palmroth, M., Turc, L., Battarbee, M., Pfau-Kempf, Y., Dubart, M., Ganse, U., Kotipalo, L., Tarvus, V., and Workayehu, A.: Magnetosheath dynamic pressure enhancements associated with a solar wind rotational discontinuity: Results from a hybrid-Vlasov simulation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2111, https://doi.org/10.5194/egusphere-egu24-2111, 2024.
Simone Di Matteo, Christos Katsavrias, Larry Kepko, and Nicholeen Viall
Mesoscale transient structures affecting the solar wind-magnetosphere coupling can be either generated in the near-Earth environment or already present in the pristine solar wind. Among the solar wind mesoscale structures, in recent years, there has been a growing attention to Periodic Density Structures (PDSs), that are quasi-periodic enhancements of solar wind density ranging from a few minutes to a few hours. These structures have been extensively observed in remote sensing observations of the solar corona, and in in situ observations up to 1 AU where they manifest radial length scales (Lx) greater than or equal to the size of the Earth’s dayside magnetosphere, i.e., from tens to hundreds Earth’s radii (RE). The PDSs have significant impact on the dynamics of the Earth’s magnetosphere and space weather for example driving Ultra-Low-Frequency (ULF) waves and affecting the dynamics and precipitation of electrons in the outer radiation belt. One key aspect to understand the PDSs role in the dynamics of space weather is to characterize their 3D size scales. Current interplanetary multi-spacecraft observations mostly occur at spatial separations unable to measure the 3D size scale of PDSs. Here, we focused on high density slow solar wind intervals observed by the Wind and ARTEMIS-P1 spacecraft. We classified solar wind parcels based on the occurrence or not of quasi periodic density enhancements. When both spacecraft observe PDSs, we further classify each interval based on the level of coherence of the relative periodicities. Combining our results with a simulation of PDSs transit, we provide, for the first time, an estimate of the PDSs azimuthal size scale, that is their extent in the direction perpendicular to the Sun-Earth direction. For two PDSs groups with radial length scales of Lx1≈86 RE and Lx2≈35 RE, we obtained azimuthal scales of Ly1≈340 RE and Ly2≈187 RE. After discussing the consequence of these findings in the context of solar wind-magnetosphere coupling, we remark that the magnetosphere response to PDS become even more relevant when these structures are compressed in Stream Interaction Regions (SIRs) creating larger fluctuations in solar wind density/dynamic-pressure. Finally, we select time intervals of PDSs in SIRs and, using GOES and RBSP constellations, we investigate the PDSs geo-effectiveness in term of ULF waves and outer belt/GEO electron response.
How to cite:
Di Matteo, S., Katsavrias, C., Kepko, L., and Viall, N.: Solar Wind Periodic Density Structures: Size Scales and Geo-effectiveness, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14825, https://doi.org/10.5194/egusphere-egu24-14825, 2024.
12:20–12:30
Discussion
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Lucile Turc, Martin Archer, Hongyang Zhou, Primoz Kajdic, Xochitl Blanco-Cano, Yann Pfau-Kempf, Terry Liu, Yu Lin, Nick Omidi, Adrian LaMoury, Sun Lee, Savvas Raptis, David Sibeck, Hui Zhang, Yufei Hao, Marcos Silveira, Boyi Wang, and Minna Palmroth
Solar wind directional discontinuities can generate transient mesoscale structures upstream of Earth's bow shock, which can have a global impact on the near-Earth environment. Understanding the formation conditions of these transient structures is crucial to evaluate their contribution to solar wind-magnetosphere coupling. Hot flow anomalies (HFAs) are thought to be created only by tangential discontinuities, and develop where the discontinuities intersect the shock. Foreshock bubbles, on the other hand, are associated with both tangential and rotational discontinuities, and are generated before the discontinuities reach the bow shock, as they form due to foreshock suprathermal ions accumulation on the upstream side of the discontinuities. Here we present the results of a global 2D hybrid-Vlasov simulation of the interaction of a rotational discontinuity with near-Earth space performed with the Vlasiator model. As the discontinuity enters the simulation domain, a foreshock bubble forms duskward of the Sun-Earth line, where the foreshock is initially located. Shortly after the discontinuity makes first contact with the bow shock at the subsolar point, we find that a structure with enhanced temperature and strongly deflected flows develops at the intersection of the discontinuity with the bow shock. This structure displays typical features of an HFA. This suggests that both a foreshock bubble and an HFA can be generated concurrently by a single directional discontinuity, and that a rotational discontinuity can lead to HFA formation in some conditions. We compare the ion distribution functions inside the foreshock bubble and the HFA, and find significant solar wind core heating within the HFA, as expected from spacecraft observations. We discuss how the properties of the structures vary spatially and temporally, providing global context to localised spacecraft measurements.
How to cite:
Turc, L., Archer, M., Zhou, H., Kajdic, P., Blanco-Cano, X., Pfau-Kempf, Y., Liu, T., Lin, Y., Omidi, N., LaMoury, A., Lee, S., Raptis, S., Sibeck, D., Zhang, H., Hao, Y., Silveira, M., Wang, B., and Palmroth, M.: A rotational discontinuity can generate both a foreshock bubble and a hot flow anomaly, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20429, https://doi.org/10.5194/egusphere-egu24-20429, 2024.
Niki Xirogiannopoulou, Oleksandr Goncarov, Jana Safrankova, and Zdenek Nemecek
The foreshock is a turbulent region located upstream of the quasi parallel bow shock. It is dominated by waves and reflected back-streaming particles that interact with each other and result in the creation of different foreshock phenomena. Xirogiannopoulou et al. (2023) found that the deceleration of the solar wind in the foreshock region plays a major role in the creation of subsolar structures with enhanced density or/and magnetic field magnitude, like plasmoids, SLAMS and mixed structures. Moreover, they have found that their formation is increasing with increased velocity of the pristine solar wind. Previous studies, established that foreshock structures are connected with MSH jets (Raptis et al., 2022). Simultaneously, Koller et al. (2023) researched the connection between the MSH jets and solar wind structures and concluded that the high-speed streams (HSS) create a more favorable environment for the jet creation. Following these results, we use measurements of the Magnetospheric Multiscale Spacecraft (MMS) and OMNI solar wind database between the years 2015 and 2018 and present a statistical analysis considering the presence of solar wind phenomena and their effect in the appearance rate of the compressive foreshock structures. We attempt to explore the origin of these structures and analyze their connection with the notable decrease (10–15 %) of the solar wind speed inside the foreshock region.
How to cite:
Xirogiannopoulou, N., Goncarov, O., Safrankova, J., and Nemecek, Z.: Solar wind deceleration in the foreshock as the source of the foreshock compressive structures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8084, https://doi.org/10.5194/egusphere-egu24-8084, 2024.
X3.12
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EGU24-3590
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ECS
A Comparative Study of Energy Conversions Associated with Collisionless Shocks and Magnetic Reconnection in the near-Earth Environment
(withdrawn)
Souhail Dahani, Benoit Lavraud, Vincent Génot, Sergio Toledo-Redondo, Rungployphan Kieokaew, Naïs Fargette, Daniel Gershman, Barbara Giles, Roy Torbert, and James Burch
X3.13
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EGU24-3388
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ECS
3D Hybrid simulation of the self-consistent propagatinginterplanetary shock wave in the Solar Wind
(withdrawn)
François Ginisty, Dominique Fontaine, Philippe Savoini, and Emanuele Cazzola
X3.14
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EGU24-9214
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ECS
Formation of Standing Whistler Waves in Earth's Magnetosheath
(withdrawn)
Yang Wang
X3.15
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EGU24-10721
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ECS
On the Conservation of Spectral Properties across Interplanetary Shocks in the Inner Heliosphere
(withdrawn)
Byeongseon Park, Alexander Pitňa, Jana Safrankova, Zdenek Nemecek, Oksana Kruparova, and Vratislav Krupar
Ahmad Lalti, Yuri V. Khotyaintsev, and Daniel B. Graham
The mechanism of electron heating across collisionless shocks remains an open question. The mechanisms suggested to address this problem revolve around the adiabatic or the non-adiabatic\stochastic dynamics of electrons across the shock. In this letter, we analyze the evolution of the electron velocity distribution function observed across 313 shocks with 1.7<MA<48. We use a Liouville mapping technique to show that the electron heating mechanism shifts from predominantly adiabatic to predominantly non-adiabatic as the Alfvenic Mach number in the de Hoffmann-Teller frame increases. We also show that for shocks with non-adiabatic heating of electrons, the heating mechanism is consistent with the stochastic shock drift acceleration (SSDA) mechanism.
How to cite:
Lalti, A., Khotyaintsev, Y. V., and Graham, D. B.: Electron heating at quasi-perpendicular collisionless shocks: adiabatic vs non-adiabatic , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17436, https://doi.org/10.5194/egusphere-egu24-17436, 2024.
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The day-to day variability of quiet-time ionosphere is surprisingly high even during periods of negligible solar forcing. Relatively well understood is the high-latitude variability where the solar wind is directly driving the high latitude currents, convection electric field or polar aurorae. But the current understanding does not allow to accurately model the ionospheric state during the quiet-time conditions at mid- and low-latitudes. Surprising effects remain even at mid-latitudes, including for instance double daily maxima of ionospheric critical frequency. European Space Agency's SWARM satellite constellation measurements allow the characterization of the upper atmospheric conditions and dynamics for already more than 10 years. The analysis of SWARM electron density and electric field data already showed that the ionosphere at mid-latitudes shows a non-negligible variability without a-priori solar driver, during negligible variations both in X-ray/EUV fluxes and missing disturbances in the solar wind. This often significant ionospheric variability currently remains unexplained, and further studies need to evaluate contributions by couplings from below comparing with those from above, i.e. checking the frequencies matching the foreshock waves with the local field-line resonances.
After efforts to properly select such "solar-quiet" periods, we compare the SWARM-detected variability trying to relate them to observations of magnetospheric ULF waves and configurations of the Earth foreshock mainly infered from the NASA's THEMIS satellite fleet and Wind solar wind observations.
How to cite:
Urbar, J.: Evaluating the effects of the Earth's foreshock configurations on the "quiet-time" ionosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18654, https://doi.org/10.5194/egusphere-egu24-18654, 2024.
Quanming Lu, Ao Guo, Zhongwei Yang, San Lu, and Rongsheng Wang
With the help of a two-dimensional (2-D) particle-in-cell (PIC) simulation model, we investigate the long-time evolution of a quasi-parallel shock. Part of upstream ions are reflected by the shock front, and their interactions with the incident ions excite low-frequency magnetosonic waves in the upstream. Detailed analyses have shown that the dominant wave mode is caused by the resonant ion-ion beam instability, and the wavelength can reach tens of the ion inertial lengths. Although these plasma waves are directed toward the upstream in the upstream plasma frame, they are brought by the incident plasma flow toward the shock front, and their amplitude is enhanced during the approaching. The interaction of the upstream plasma waves with the shock leads to the cyclic reformation of the shock front. When crossing the shock front, these large-amplitude plasma waves are compressed and evolve into current sheets in the transition region of the shock. At last, magnetic reconnection occurs in these current sheets, accompanying with the generation of magnetic islands. Simultaneously, there still exist another kind of plasma waves with the wavelength of several ion inertial lengths in the ramp of the shock. The current sheets in the transition region are distorted and broken into several segments when this kind of plasma waves are transmitted into the downstream, where magnetic reconnection and the generated islands have a much smaller size.
How to cite:
Lu, Q., Guo, A., Yang, Z., Lu, S., and Wang, R.: Upstream plasma waves and downstream magnetic reconnection at a reforming quasi-parallel shock, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-85, https://doi.org/10.5194/egusphere-egu24-85, 2024.
Martin Lindberg, Alice Wallner, Sofie Berglund, and Andris Vaivads
We use the Magnetospheric Multiscale mission to study electron kinetic entropy across Earth's quasi-perpendicular bow shock. We perform a statistical study of how the change in electron entropy depends on the different plasma parameters associated with a collisionless shock crossing. We find that the change in electron entropy exhibits strong correlations with upstream electron plasma beta, Alfvén Mach number, and electron thermal Mach number. The source of entropy generation is investigated by correlating the change in electron entropy across the shock to the measured electric and magnetic field wave power strengths for different frequency intervals within different regions in the shock transition layer. The electron entropy change is observed to be greater for higher electric field wave power within the shock ramp and shock foot for frequencies between the lower hybrid frequency and electron cyclotron frequency. This implies electrostatic waves are important for electron kinetic entropy generation at Earth's quasi-perpendicular bow shock but also for the non-adiabatic electron heating at quasi-perpendicular shocks.
How to cite:
Lindberg, M., Wallner, A., Berglund, S., and Vaivads, A.: Statistical Study of Electron Kinetic Entropy Generation at Earth's Quasi-perpendicular Bow Shock, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1836, https://doi.org/10.5194/egusphere-egu24-1836, 2024.
Keiichi Ogasawara, Harald Kucharek, Berndt Klecker, Maher Dayeh, and Robert Ebert
3D velocity distribution functions (VDFs) of He+ pickup ions (PUIs) were used to trace local physical processes around interplanetary shocks. He+ PUIs are measured by PLasma And SupraThermal Ion Compostion (PLASTIC) instrument onboard the Solar Terrestrial Relations Observatory (STEREO) in an unprecedented cadence and angular/velocity resolutions with mass and charge state unambiguously determined. We focused on the VDFs in terms of the interplanetary magnetic field orientation in the solar wind frame and indipendently evaluated the acceleration, heating, and pitch-angle scattering for both perpendicular and parallel shocks with notable differences. For the perpendicular shock: (a) Reflected and energized particles were found in the upstream, and the PUI properties were isolated between upstream and downstream, (b) Strong heating is observed in the sheath region, (c) Suprathermal particles are found in the sheath region and attributed to the compression within the solar wind, and (d) Universal pitch-angle scattering were found through out the ICME. For the parallel shock: (a) Locaized heating and acceleration were found around the shock location, (b) Harder suprathermal particle distributions were found near the shock, suggesting diffusive shock processes, (c) Weak or no sheath heating was observed, and (d) Pitch angle scattering were correlated with magnetic field power spectral density at the Helium cyclotron.
How to cite:
Ogasawara, K., Kucharek, H., Klecker, B., Dayeh, M., and Ebert, R.: Helium pickup ion 3D velocity distributions at interplanetary shocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2220, https://doi.org/10.5194/egusphere-egu24-2220, 2024.
Tsz Kiu Wong Chan, Tomas Karlsson, and Sofia Bergman
Properties of the region upstream of planetary bow shocks depend strongly on the direction of the interplanetary magnetic field. For quasi-parallel bow shocks, part of the solar wind ions are reflected back upstream from the shock and this reflected ion population triggers instabilities resulting in a turbulent region. In the quasi-parallel case, reflected particles travel far upstream, creating an extended turbulent foreshock region. Within this region, Short Large-Amplitude Magnetic Structures (SLAMS) can frequently be found, which are suggested to play a pivotal role in the formation of planetary bow shocks. Yet many properties of SLAMS are not well known at Earth and even less so at other planets.
Here we present results on the occurrence and other properties of SLAMS at the Martian foreshock with the help of magnetic field and ion data from NASA's Mars Atmosphere and Volatile Evolution Mission (MAVEN). SLAMS are identified by three criteria. First, a magnetic field three times stronger than the background magnetic field is required. Second, SLAMS should have an elliptic polarization so that it can be differentiated from a shock oscillation. Last, it takes place upstream of the bow shock. The results presented here can offer comparative insights with SLAMS at Earth for exploring potential dependencies on system size and other magnetospheric parameters.
How to cite:
Wong Chan, T. K., Karlsson, T., and Bergman, S.: Statistical study of SLAMS at the Martian foreshock, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3121, https://doi.org/10.5194/egusphere-egu24-3121, 2024.
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Sofia Bergman, Tomas Karlsson, and Tsz Kiu Wong Chan
Short Large-Amplitude Magnetic Structures (SLAMS) are common magnetic field signatures observed in the foreshock region of collisionless quasi-parallel shocks. SLAMS are non-linear isolated structures, defined to have an amplitude of more than 2 times the background magnetic field. They have been suggested to grow from ultra-low frequency (ULF) waves that are common in the foreshock region, and are believed to play important roles in the formation of quasi-parallel shocks, influencing the properties and dynamics of the shock and also associated particle energization.
In this work, we use data from the Cluster and Magnetospheric Multiscale (MMS) missions to statistically study the properties of SLAMS in the foreshock region of Earth. We use an automated method to detect SLAMS in the data, producing a comprehensive database of SLAMS detections. The size, morphology and propagation velocity of SLAMS are then studied using statistical approaches, investigating the dependence on several parameters, such as amplitude, upstream conditions and distance from the bow shock.
How to cite:
Bergman, S., Karlsson, T., and Wong Chan, T. K.: Statistical properties of Short Large-Amplitude Magnetic Structures (SLAMS) in the foreshock region of Earth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3125, https://doi.org/10.5194/egusphere-egu24-3125, 2024.
Ion reflection is known to be a key component of particle energisation and heating in super-critical collisionless shockwaves. As a source of free energy, reflected ions drive stream instabilities in the shock foot, create magnetic perturbations, and contribute to magnetic field amplification in the upstream and downstream regions of quasi-perpendicular shocks. Where ions reflect from the shock ramp multiple times, a longer dwell time in the shock foot allows for more opportunities for interaction with non-stationary and turbulent shock processes, which can result in injection into processes such as diffusive shock acceleration and shock drift acceleration. To characterise the pathway to multiple ion reflection, we perform a series of 2D and 3D hybrid particle-in-cell simulations (fluid electron, particle ions) over a parameter range typical of Earth’s bow shock, varying Mach number, plasmas betas, and the angle between the shock normal and upstream magnetic field (θBn). This enables a parametric investigation of the density fraction of multiply reflected ions both upstream and downstream of the shock, for protons and for heavier ion components of the solar wind such as He2+. We discuss methods for identification of multiply-reflected ions in kinetic plasma simulations, corresponding analogues for observations (where available), and investigate their impact on shock energetics. By examining the partial moments of reflected ions in two- and three-dimensional simulations, we also explore which shock processes drive multiple reflection.
How to cite:
Gingell, I. and Madanian, H.: Hybrid simulations of multiple reflection of protons and heavy ions at Earth’s bow shock, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3966, https://doi.org/10.5194/egusphere-egu24-3966, 2024.
Primoz Kajdic, Xochitl Blanco-Cano, Diana Rojas Castillo, Martin Archer, Lucile Turc, Yann Pfaum-Kempf, Adrian LaMoury, Terry Liu, Savvas Raptis, Marcos Vinicius, Sun Lee, Yao Shutao, Yufei Hao, David Sibeck, Hui Zhang, Nojan Omidi, Boyi Wang, Yu Lin, and Philippe Escoubet
Transient upstream mesoscale structures (TUMS) are an important topic in the field of research of the near-Earth environment. These events form upstream of the Earth's bow shock and can perturb regions downstream it, i.e. magnetosheath and magnetopause. They can even affect the magnetosphere and ionosphere causing a range of space weather phenomena during periods without noticeable solar activity. There is still much to learn about the TUMS and the way they interact with the near-Earth environment. We are only beginning to understand how the different types of the TUMS relate to each other. In the past it has been shown that traveling foreshocks may contain foreshock cavitons, spontaneous hot flow anomalies and foreshock compressional boundaries (FCB). Here we present the first evidence, that traveling foreshocks may be bounded on at least one of their edges by hot flow anomalies (HFA) and by events that look like hybrids between HFAs and FCBs. We show two case studies observed by the Cluster and MMS constellations. Such studies enable us to better understand all the ways in which the solar-terrestrial interactions occur.
How to cite:
Kajdic, P., Blanco-Cano, X., Rojas Castillo, D., Archer, M., Turc, L., Pfaum-Kempf, Y., LaMoury, A., Liu, T., Raptis, S., Vinicius, M., Lee, S., Shutao, Y., Hao, Y., Sibeck, D., Zhang, H., Omidi, N., Wang, B., Lin, Y., and Escoubet, P.: Hot Flow Anomalies Delimiting Traveling Foreshocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4145, https://doi.org/10.5194/egusphere-egu24-4145, 2024.
Xochitl Blanco-Cano, Diana Rojas-Castillo, and Primoz Kajdic
In recent years we have learnt that foreshock transients play an influential role in solar wind coupling with Earth’s magnetosphere. These transients include Spontaneous Hot Flow Anomalies (SHFAs) which are characterized by dips in magnetic field magnitude and ion density, enhanced temperature, and are surrounded by ultra low frequency waves. SHFAs share some characteristics with hot flow anomalies but their formation mechanism does not require a discontinuity in the solar wind. SHFAs evolve from caviton interaction with backstreaming ions. We use Cluster and MMS magnetic field and plasma data to study SHFAs internal structure and their evolution. We find that SHFA can occur not only deep in the foreshock as initially thought, but they can also been observed near the foreshock boundary where higher frequency waves (f ∼ 1 Hz) exist. We also investigate the properties of velocity distribution functions inside these transients, and their influence on bow shock structure.
How to cite:
Blanco-Cano, X., Rojas-Castillo, D., and Kajdic, P.: Spontaneous Hot Flow Anomalies at Earth’s foreshock., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6483, https://doi.org/10.5194/egusphere-egu24-6483, 2024.
In this paper, two-dimensional hybrid simulations are used to study wave excitation and evolution throughout a low-Mach number quasi-parallel shock. Simulation results show that quasi-parallel fast magnetosonic waves, ion Bernstein waves with harmonics and possible Alfven/ion cyclotron waves can be excited in the upstream region, and their small phase velocities compared to injected flow velocity results in the convection to the shock front where they are mode converted into several groups of downstream waves, including Alfven waves along the directions parallel to downstream average magnetic fields and perpendicular to the shock normal, the quasi-perpendicular kinetic slow waves and possible kinetic Alfven waves. We suggest that downstream Alfven waves originate from the mode conversion of upstream quasi-parallel fast magnetosonic waves with left-hand polarization in the downstream rest frame under helicity conservation, while the downstream left-hand polarized kinetic slow waves and right-hand polarized kinetic Alfven waves can be from the upstream quasi-perpendicular ion Bernstein waves.
How to cite:
Hao, Y., Lu, Q., Wu, D., and Xiang, L.: Wave Activities Throughout a Low-Mach Number Quasi-Parallel Shock: 2-D Hybrid Simulations , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9451, https://doi.org/10.5194/egusphere-egu24-9451, 2024.
Yuri Khotyaintsev, Daniel Graham, Domenico Trotta, Ahmad Lalti, and Andrew Dimmock
Reflection of a fraction of incoming ions is a vital dissipation mechanism for super-critical shocks. Such reflected ions provide a significant contribution to the downstream ion temperature increase. Understanding ion dynamics is crucial for the characterization of the shocks. It is needed to provide an equation of state that connects the upstream and downstream parameters for given shock parameters. The reflection depends on the detailed structure of the electromagnetic fields in the shock transition region. The ion-scale structure is strongly affected by the shock non-stationarity. To characterize the spatiotemporal evolution of the shock structure and ion reflection, we combine observations of several in-situ shock events by MMS with hybrid simulations performed for the specific parameters of the observed shocks. We find that the ion reflection is strongly affected by the structure imposed by the ripples. The reflection is very patchy, with regions of strong and weak ion reflection.
How to cite:
Khotyaintsev, Y., Graham, D., Trotta, D., Lalti, A., and Dimmock, A.: Ion dynamics in quasi-perpendicular nonstationary shocks: comparison between MMS observations and hybrid modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16745, https://doi.org/10.5194/egusphere-egu24-16745, 2024.
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