ST2.2
Orals: Thu, 27 Apr | Room 0.16
Magnetic holes are coherent structures associated with a strong depression in the magnetic field amplitude. Such structures are ubiquitous in space plasmas and are observed in the solar wind, in planetary bow shocks and magnetosheaths, in the Earth's magnetotail and around comets. Magnetic holes may have very different sizes and properties. The largest ones have a size of hundreds of ion gyroradii while the smallest ones are sub-ion scale structures of the order of a few electron gyroradii. The drop in magnetic field amplitude associated with magnetic holes is often sustained by an increase in plasma density and enhanced ion and electron temperature anisotropies, with temperatures that are typically higher in the plane perpendicular to the local magnetic field. These properties seem to suggest that the generation of magnetic holes may result from the nonlinear evolution of mirror modes whose growth is fed by perpendicular temperature anisotropies and that are characterized by anticorrelated magnetic field and density perturbations. Some observational and numerical studies seem to support the idea of a scenario in which magnetic holes are generated by the mirror instability but in many cases this picture is not consistent with observations, especially in the case of sub-ion scale magnetic holes for which a number of possible generation mechanisms have been considered. Hence, the origin of magnetic holes is still controversial and under debate.
Plasma turbulence is also known as a driver for the generation of coherent structures and may play a key role in the formation of magnetic holes, especially in the solar wind and in the Earth's magnetosheath that are in a turbulent state. Indeed, numerical simulations of plasma turbulence show that sub-ion scale magnetic holes can develop self-consistently out of small scale magnetic fluctuations that locally reduce the magnetic field amplitude and trap hot electrons. However, it is still unclear how such small scale fluctuations can emerge in a turbulent plasma where energy is typically injected at large scales. In this work, we study the formation of sub-ion scale magnetic holes by means of fully kinetic particle-in-cell simulations of plasma turbulence. We show that by injecting energy at scales relatively large with respect to ion scales, the turbulence naturally tends to generate sub-ion scale electron velocity shear layers associated with elongated magnetic field grooves. These elongated magnetic dips then become unstable and break up into sub-ion scale magnetic holes characterized by an intense azimuthal electron current and a strong perpendicular electron temperature anisotropy. We show that the properties of magnetic holes generated by this mechanism are consistent with satellite observations. Our results may provide a possible explanation of how magnetic holes develop in a realistic turbulent environment.
How to cite: Arrò, G., Pucci, F., Califano, F., and Lapenta, G.: Generation of sub-ion scale magnetic holes from electron shear flow instabilities in plasma turbulence, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-10616, https://doi.org/10.5194/egusphere-egu23-10616, 2023.
Modeling the interaction of solar wind discontinuities with the bow shock-magnetosheath-magnetopause system is an important step in comprehending the effects of solar wind structures on the magnetosphere. Our procedure is to first run a global MHD simulation to predict the overall configuration of the solar wind-magnetosphere system before the discontinuity interacts with the bow shock. Then fields and plasma moments within a large sub-domain of the global MHD simulation are used to set the initial conditions of an implicit PIC simulation of the interaction of the discontinuity with the dayside magnetosphere. This procedure allows us to follow the evolution of kinetic processes as the discontinuity interacts with the bow shock and propagates through the magnetosheath before impacting the dayside magnetopause. In this presentation, we show some results of the interaction of a rotational discontinuity where the interplanetary magnetic field, initially southward, turns northward. As expected, the discontinuity slows down abruptly after interacting with the bow shock, the transverse component of the magnetic field being greatly enhanced in the process. While the initial MHD state of the magnetosheath was laminar, kinetic waves and instabilities lead to a turbulent state for all plasma moments and electromagnetic fields. In particular, transients are observed ahead of the discontinuity as it propagates Earthward. At later stages of the simulation, the discontinuity interacts with the magnetopause. Magnetic field lines are bent strongly in the transverse direction, affecting reconnection processes with the production of large magnetic flux ropes.
How to cite: Berchem, J., Lapenta, G., Escoubet, P., and Wing, S.: Kinetic modeling of the interaction of solar wind discontinuities with the bow shock-magnetosheath-magnetopause system, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4522, https://doi.org/10.5194/egusphere-egu23-4522, 2023.
Counter-streaming particles reflected from the Earth's bow shock towards the Sun build up the ion foreshock, exciting right-handed ultra-low frequency (ULF) waves, which convect with the solar wind back to the bow shock. As these waves move Earthward, they steepen and interact with each other, forming a complex wave field consisting of various foreshock structures. Observations of foreshock structures have classified them as, for example, ULF waves, shocklets, short large-amplitude magnetic structures (SLAMS), cavitons, and spontaneous hot flow anomalies (SHFAs). We present results from a high Mach number 2D-3V hybrid-Vlasov Vlasiator simulation of the Earth's bow shock and foreshock during quasi-radial IMF and place them in the context of spacecraft observations. We combine spatial analysis of bulk characteristics within the foreshock with virtual spacecraft observations to evaluate the morphology of foreshock structures as they form, and how they subsequently evolve as they approach the Earth's bow shock.
How to cite: Battarbee, M., Archer, M., Hietala, H., Plaschke, F., Palmroth, M., and Turc, L. and the the Vlasiator team: Morphology and evolution of foreshock structures in a high-Mach number hybrid-Vlasov simulation of Earth's magnetosphere, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15282, https://doi.org/10.5194/egusphere-egu23-15282, 2023.
The foreshock, extending upstream of the quasi-parallel shock and populated with shock-reflected particles, is home to intense wave activity in the ultra-low frequency range. The most commonly observed of these waves are the '30-second' waves, fast magnetosonic waves propagating sunward in the plasma rest frame, but carried earthward by the faster solar wind flow. These waves are thought to be the main source of Pc3 magnetic pulsations (10-45 s periods) in the dayside magnetosphere, but how the waves can transmit through the bow shock and across the magnetosheath had remained unclear. Global hybrid-Vlasov simulations performed with the Vlasiator model provide us with the global view of foreshock wave transmission across near-Earth space. We find that the foreshock waves modulate the plasma parameters just upstream of the bow shock, which in turn periodically changes the shock compression ratio and the downstream pressure. This launches fast-mode waves propagating through the magnetosheath all the way to the magnetopause, where they can further transmit into the dayside magnetosphere. We compare our numerical results with MMS observations near the subsolar point, where we identify earthward-propagating fast-mode waves at the same period as the foreshock waves, consistent with our simulation results. Our findings show that the wave propagation across the bow shock is much more complex than the simple direct transmission of the foreshock waves which was inferred in early studies.
How to cite: Turc, L., Roberts, O. W., Verscharen, D., Dimmock, A. P., Kajdic, P., Palmroth, M., Pfau-Kempf, Y., Johlander, A., Dubart, M., Kilpua, E. K. J., Takahashi, K., Takahashi, N., Battarbee, M., and Ganse, U.: Transmission of foreshock waves through Earth's bow shock, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6637, https://doi.org/10.5194/egusphere-egu23-6637, 2023.
Foreshock ultralow frequency (ULF) waves play an important role in the dynamics upstream of planetary bow shocks and can affect the downstream magnetosheath region. Due to limited available spacecraft measurements, the waves are often analyzed with incomplete information about their overall spacial structure. Common wave vector analysis techniques built around these limitations often invoke the divergence free condition of the magnetic field without considering the possibility that the wave amplitude profile could have a strong spacial dependence. We explore the consequences of this assumption in the Earth's ion foreshock using both ARTEMIS spacecraft data and a 2-D hybrid Vlasov simulation conducted using the Vlasiator code. The observed foreshock ULF waves have a finite extent in the direction perpendicular to the Interplanetary Magnetic Field, and incorrect application of standard techniques at the boundary yields a false wave vector orientation that may be used as a novel edge detection method. Our results stand as a cautionary tale for wave analysis in other space physics contexts where the wave geometry is less clear.
Supported by NASA Grant 80NSSC20K0801. Vlasiator is developed by the European Research Council Starting grant 200141-QuESpace, and Consolidator grant GA682068-PRESTISSIMO received by the Vlasiator PI. Vlasiator has also received funding from the Academy of Finland. See www.helsinki.fi/vlasiator
How to cite: Dorfman, S., Zhang, K., Turc, L., Ganse, U., and Palmroth, M.: Probing the foreshock wave boundary, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11073, https://doi.org/10.5194/egusphere-egu23-11073, 2023.
Magnetic flux ropes with a wide range of scale sizes generally have high magnetic helicity, a magnetohydrodynamic (MHD) quantity that characterizes the knottedness of the field lines that can be used to identify flux rope structures. The identification and analysis of structures moving across boundaries such as the Earth's bow shock will give insight into how their properties change across this boundary as well as further our understanding of the interrelation between these structures. Recent spacecraft missions are returning higher time resolution data than before, allowing for more advanced studies of this phenomenon. Using high time-resolution data from the Magnetospheric Multiscale (MMS) mission and Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission, we identify small-scale flux ropes using wavelet analysis and determine how they change across boundaries. Wavelet analysis of single-spacecraft data can produce better resolved time and spatial information that will complement other methods of flux rope identification. Wavelet transforms are performed across hours-long intervals, organized by the orbit configuration of the spacecraft. The resulting spectrograms are then searched to identify small-scale structures. A number of parameters, including duration, scale size, maximum magnetic field, and average plasma temperature of the flux rope intervals identified are also recorded and summarized. Comparing the values of magnetic field, plasma beta, and other parameters at the corresponding times and locations leads to interpretations for the flux rope events such as whether they are compressed, decelerated, or undergo any other changes as they evolve.
How to cite: Harvey, R. and Hu, Q.: Observational Analysis of Small-scale Structures in the Earth's Magnetosheath, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9082, https://doi.org/10.5194/egusphere-egu23-9082, 2023.
Hot flow anomalies (HFAs) are typical and important foreshock transients characterized by large flow deflection and plasma heating. HFAs can deform the Earth’s bow shock by dynamic pressure perturbation resulting in disturbance in the magnetosphere and ionosphere. Traditionally, HFAs are believed to be associated with discontinuities. But recently, HFA-like structures were simulated by an magnetohydrodynamics (MHD) model without the discontinuity prerequisite. In this study, we give three HFA examples to verify this MHD formation mechanism. For the first event, we use multi-points observation from the THEMIS mission to track the formation of the HFA accompanying with a density depletion upstream. For the other two events, we compare observations from the MMS mission and the ARTEMIS mission with the MHD simulation results using density depleted solar wind flux tubes to investigate the physical process of HFA formation. The comparison of simulation and observation shows general agreement particularly in the presence of a core with strong heating and velocity deflection, and two compression regions (shocks) with clear maxima in the ram pressure with a strongly inclined normal boundary at the leading edge and moderately inclined at the trailing edge. Agreement was better when the MHD simulations used a transient change to quasi-parallel solar wind magnetic field during the events. Result suggests that ram pressure may be an excellent diagnostic for HFAs both in the solar wind and in the magnetosheath.
How to cite: Lu, X., Zhang, H., Otto, A., Liu, T., and Chen, X.: The bow shock and magnetosheath responses to density depletion structures, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-2438, https://doi.org/10.5194/egusphere-egu23-2438, 2023.
Orals: Fri, 28 Apr | Room 0.16
In this study, we present the analysis of steepened ultra-low frequency (ULF) waves in the foreshock region upstream of Mars’ bow shock observed by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft at Mars. A survey of MAVEN magnetic field and plasma measurements shows quasi-periodic gradual increases followed by a sharp decrease in the magnetic field magnitude (Btotal). Higher frequency waves were also commonly, but not always, observed at the trailing edge of the large-amplitude increase in Btotal. These observations are consistent with the signatures of shocklets observed in the solar wind region upstream of Earth’s and planetary bow shocks. Shocklets are believed to be formed as a result of the steepening of fast magnetosonic waves generated by reflected ions in the quasi-parallel foreshock region. We also performed the minimum variance analysis (MVA) and statistical analysis technique to determine the wave properties (e.g. polarization, wave propagation, amplitude and frequency) of the shocklets and higher frequency waves observed in its trailing edge. Our results showed that these shocklets are left-handed polarized in the spacecraft frame, with mean amplitude δB/B of ~3.5 and time separation between adjacent shocklet events of ~40s. We also analyzed measurements (ions and electrons) from MAVEN’s plasma instruments to investigate the energization process of the particles during the observations of shocklets. We will discuss the possible generation mechanisms for these steepened ultra-low frequency waves at Mars, and any implications for the martian plasma environment downstream of Mars’ bow shock.
How to cite: Poh, G., Espley, J., Xu, S., Le, G., Romanelli, N., Halekas, J., DiBraccio, G., and Gruesbeck, J.: MAVEN Observations of Steepened Ultra-Low Frequency Waves in the Upstream Martian Foreshock Region, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-10536, https://doi.org/10.5194/egusphere-egu23-10536, 2023.
In the foreshock region of planetary and terrestrial bow shocks, interaction of reflected solar wind ions with the incident solar wind and the interplanetary magnetic field gives rise to a variety of transient plasma structures and instabilities, and the ion dynamics and ion kinetic scale processes drive the foreshock environment. In this comparative study, we consider specific examples of transient foreshock structures upstream of Mars and Earth and contrast differences between theri formation process, contributing ion populations, and source region of ion populations. Due to the smaller size of Mars and its bow shock compared to Earth and with respect to upstream ion convective gyroradius, reflected ions with hybrid trajectories that straddle between the quasi-perpendicular and quasi-parallel bow shocks can contribute to formation of foreshock transients. The size of transient foreshock structures upstream of Mars differs compared to Earth, which influences their propagation and impact through the magnetosheath and lower plasma boundaries.
How to cite: Madanian, H.: Formation of Transient Foreshock Structures Upstream of Mars and Earth: A Comparative Study, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4004, https://doi.org/10.5194/egusphere-egu23-4004, 2023.
Interplanetary shocks are some of the main drivers of geomagnetic storms. Before they can impact the geomagnetic environment, they propagate through the magnetosheath where their properties and geometry can be modified. What is the velocity of interplanetary shocks propagating through the magnetosheath? Previous numerical simulations and observations have given a wide range of apparently contradictory answers to this question, but they seem to all agree that interplanetary shocks generally slow down as they enter the magnetosheath: the interplanetary shocks’ velocity in the magnetosheath have been reported to be between 0.25 and 0.93 times their velocity in the solar wind. In this work, we offer two competing simple models to predict the propagation velocity of shocks through the magnetosheath. These models are applied to a list of shocks detected by currently operational spacecraft (e.g. Wind, MMS) as well as to results obtained from a hybrid PIC simulation. We show that our models both reconcile previous results and imply that interplanetary shocks could - in certain space weather-relevant situations - travel faster in the magnetosheath than they did in the solar wind.
How to cite: Moissard, C., Bernal, A., Savoini, P., Fontaine, D., Modolo, R., David, V., and Michotte de Welle, B.: On the Speed of Interplanetary Shocks Propagating through the Magnetosheath, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9423, https://doi.org/10.5194/egusphere-egu23-9423, 2023.
The Earth’s magnetosheath is a dynamic region and its properties strongly depend on the angle between the bow shock normal and the solar wind magnetic field (θbn). If the shock is quasi-parallel (θbn < 45°), the magnetosheath is magnetically connected to the foreshock, causing strong fluctuations and structures propagating from upstream to downstream. A quasi-perpendicular shock (θbn > 45°) produces a less structured and more stationary magnetosheath characterized by compression and high ion temperature anisotropy. These distinct configurations make it possible to study how different plasma environments affect various processes such as turbulence, heating, and wave-particle interactions. Therefore, such studies require an accurate classification of the magnetosheath. This is not easily achieved, especially close to the magnetopause where the shock crossing for the plasma of interest cannot be observed.
Previously, Karlsson et al. (2021) used data from the Cluster mission to propose a promising classification method using local measurements of the magnetic field standard deviation, high-energy ion flux, and ion temperature anisotropy. In this work, we are building on this study and extending it to the Magnetospheric Multiscale (MMS) mission, having a different orbit than Cluster. We compare this local classification to θbn estimated from upstream conditions and well-known bow shock models, and discuss the advantages and disadvantages of the different methods.
Reference: Karlsson, T., Raptis, S., Trollvik, H., & Nilsson, H. (2021). Classifying the magnetosheath behind the quasi-parallel and quasi-perpendicular bow shock by local measurements. Journal of Geophysical Research: Space Physics, 126, e2021JA029269.
How to cite: Svenningsson, I., Yordanova, E., Khotyaintsev, Y. V., André, M., and Cozzani, G.: Classifying the magnetosheath using local measurements from MMS, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-8664, https://doi.org/10.5194/egusphere-egu23-8664, 2023.
The magnetosheath is a region downstream of the bow shock filled with turbulent, decelerated solar wind plasma which is flowing earthwards. This solar wind flow sometimes shows signatures of localized structures with enhanced dynamic pressure, so called magnetosheath jets. These jets are often associated with low angles between the bow shock normal and the interplanetary magnetic field (IMF) direction, the so called quasi-parallel bow shock. Less often they are also found behind the quasi-perpendicular bow shock.
As jets propagate through the magnetosheath, they interact with the surrounding plasma. Studying waves inside, and in the vicinity of, jets is a step towards understanding the interaction of jets with the surrounding plasma. So far whistler waves, electrostatic waves, waves in the lower hybrid frequency range as well as low frequency waves have been reported. However, the sources of these waves are unknown. In addition, further types of waves may be associated with the jets.
We conduct a study on waves in magnetosheath jets using burst mode data of the Magnetospheric Multiscale (MMS) mission. The magnetic and electric field data are provided with a sampling rate of 8 kHz, while previous studies used data sets with much lower sampling rates. The high time resolution allows us to study different waves over a large frequency range and investigate properties of these waves. In addition, we discuss possible generation mechanisms.
How to cite: Krämer, E., Hamrin, M., Gunell, H., Karlsson, T., Steinvall, K., Goncharov, O., and André, M.: Identifying the zoo of waves in Magnetosheathjets using MMS burst data, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-550, https://doi.org/10.5194/egusphere-egu23-550, 2023.
Magnetosheath jets are dynamic pressure enhancements that are frequently observed downstream of the Earth's bow shock. Earthward propagating jets are significantly more likely to occur downstream of the quasi-parallel shock than the quasi-perpendicular shock. However, as the quasi-perpendicular geometry is the more common configuration at the Earth's bow shock, quasi-perpendicular jets can constitute a significant fraction of jets observed at Earth. Moreover, at other more quasi-perpendicular shock environments, such as at interplanetary shocks or the bow shocks of outer planets, they would be expected to form an even more significant portion of jets. We study the solar wind influence on jet formation in the quasi-parallel and quasi-perpendicular regimes by investigating jets in the Earth’s subsolar magnetosheath separately during low and high IMF cone angles. We find that during low IMF cone angles (downstream of the quasi-parallel shock) jet occurrence near the bow shock is not sensitive to other solar wind parameters. However, during high IMF cone angles (downstream of the quasi-perpendicular shock) jet occurrence is higher during low B, low n, high beta, and high MA conditions. This suggests that quasi-perpendicular jet formation is related to shock dynamics amplified by higher beta and MA. These observations from a wide range of solar wind parameters also allow us to make predictions of jet occurrence at other planetary systems.
How to cite: Vuorinen, L., Hietala, H., and LaMoury, A. T.: Solar wind parameters influencing magnetosheath jet formation: low and high IMF cone angle regimes, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9960, https://doi.org/10.5194/egusphere-egu23-9960, 2023.
Large-scale solar wind (SW) structures like coronal mass ejections (CMEs) and stream interaction regions (SIRs) significantly alter the plasma within the Earth’s magnetosheath and change the foreshock region. Thus, they modulate the number and the parameters of dynamic pressure transients in the magnetosheath, which we call magnetosheath jets. We use THEMIS spacecraft data from 2008 to 2022 to detect these jets in the magnetosheath and OMNI data for the SW within the same time range. We investigate which properties in each SW structure primarily influence the jet occurrence. We find that CMEs cause a reduction in jet occurrence due to the mix of high magnetic field strength, high plasma beta, low Mach number, and high cone angles. These conditions most likely disrupt the building of a proper foreshock region and thus hinder the major generation mechanism for jets in the magnetosheath. On the other hand, high speed streams in SIRs show favorable conditions for jet generation in all plasma parameters, most importantly due to the high probability for low cone angles, the low density, high velocity, and low magnetic field strength. We analyze how the jet parameters differ in each type of SW structure and discuss how this influences the geoeffectiveness of jets.
How to cite: Koller, F., Plaschke, F., Preisser, L., Temmer, M., Roberts, O., and Vörös, Z.: Modification of magnetosheath jet occurrence and properties within CMEs and SIRs, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-10625, https://doi.org/10.5194/egusphere-egu23-10625, 2023.
Large scale solar wind (SW) structures called Coronal Mass Ejections (CMEs) and Stream Interaction Regions (SIRs) propagate through the interplanetary medium, where they might impact Earth and cause jet-like disturbances in the magnetosheath. Such jets are short scale structures characterized by an enhancement in dynamic pressure that propagate through the Earth’s magnetosheath (EMS) transporting mass, momentum and energy being able to affect and perturb the Earth’s magnetosphere.
Jets have been studied for 20 years, but how different SW conditions triggered by CMEs and SIRs affect jet production is a topic that has only recently begun to be studied. In this work we characterize jets observed by THEMIS during a CME and a SIR passage. We find clear differences in number and size between the jets associated with the CME regions arriving at the EMS as well as in comparison with the characteristics of jets associated with the SIR passage. Comparing WIND and THEMIS data we discuss how these differences are linked to the SW conditions in the context of a recent statistical study (Koller et al. 2022) and with different jet generation mechanisms.
How to cite: Preisser, L., Plaschke, F., Koller, F., Temmer, M., Roberts, O., and Vörös, Z.: On the production of magnetosheath jets during a CME and SIR passage: A case study, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9495, https://doi.org/10.5194/egusphere-egu23-9495, 2023.
Posters on site: Fri, 28 Apr, 10:45–12:30 | Hall X4
Mirror mode waves with anticorrelated density and magnetic field perturbations have been widely observed in the planetary magnetosheaths and solar wind. In this study we examine the time evolution of proton mirror instability based on the hybrid particle simulation with the focus being on the thermodynamics of mirror waves. A set of double-polytropic (DP) laws are adopted to infer the corresponding thermodynamic conditions characterized by the polytropic exponents, γ⊥and γ. It is shown that the γ⊥, values at the saturation stages are in the ranges of γ⊥ = 0.64±0.21 and γ = 1.07±0.12 which are consistent with the observations and linear kinetic theory (Hau et al. 2021). The saturated plasma β are well fitted by the modified DP MHD mirror condition of γβ = β⊥2/(2+γ⊥β⊥) with γ⊥ ≈ 0.8, γ ≈ 1.3 which may be used as a new mirror criterion for the mirror waves observed in the solar system.
How to cite: Chang, C.-K. and Hau, L.-N.: Kinetic simulation of proton mirror instability, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3758, https://doi.org/10.5194/egusphere-egu23-3758, 2023.
Temperature anisotropy-driven instabilities such as the mirror mode and ion cyclotron instabilities are responsible for the generation of waves in the turbulent magnetosheath of planets. We present two statistical studies of mirror mode-like structures in the magnetosheaths of (mostly) unmagnetised planets such as Mars and Venus, characterised in the same way and with the same tools with the help of on-board magnetometers. In this presentation, we discuss observations by the MAVEN spacecraft. As in our companion Venus study (see poster by Volwerk et al. in the same session), we use magnetic field-only measurements to constrain and identify these quasi-linear compressive structures and discuss ways to mitigate false positive detections based on one instrument only. After calculating the residence time of the spacecraft in the Martian magnetoenvironment, we show two-dimensional statistical maps of mirror mode-like occurrence rates with respect to EUV solar flux levels, Mars Year, and atmospheric seasons. We find detection probabilities of about 1% at most, with two main regions of occurrence, one behind the collisionless shock, the other close to the induced magnetospheric boundary, with the clearest modulation of the probability due to EUV solar flux conditions. Finally, we qualitatively compare our results with past studies at Mars.
How to cite: Simon Wedlund, C., Volwerk, M., Mazelle, C., Rojas Mata, S., Stenberg Wieser, G., Futaana, Y., Halekas, J., Rojas-Castillo, D., Bertucci, C., and Espley, J.: Mirror mode-like structures around unmagnetised planets: 1. Mars as observed by the MAVEN spacecraft, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-1305, https://doi.org/10.5194/egusphere-egu23-1305, 2023.
Temperature anisotropy-driven instabilities such as the mirror mode and ion cyclotron instabilities are responsible for the generation of waves in the turbulent magnetosheath of planets. We present here a statistical study of mirror mode-like structures in the magnetosheath of Venus as observed by the Venus Express spacecraft. As in our Mars study (see poster by Simon Wedlund et al. in the same session), we use magnetic field-only measurements to constrain and identify these quasi-linear compressive structures and discuss ways to mitigate false positive detections based on one instrument only. After calculating the residence time of the spacecraft in the Venusian magnetoenvironment, we show two-dimensional statistical maps of mirror mode-like occurrence rates with respect to EUV solar flux levels, and type of bow shock (quasi-perpendicular vs quasi-parallel). We find detection probabilities of about 10% at most, with two main regions of occurrence, one behind the collisionless shock, the other close to the induced magnetospheric boundary, with the small modulation of the probability due to EUV solar flux conditions.
How to cite: Volwerk, M., Simon Wedlund, C., Mautner, D., Rojas Mata, S., Stenberg Wieser, G., Futaana, Y., Fraenz, M., Mazelle, C., Rojas-Castillo, D., Bertucci, C., and Delva, M.: Mirror mode-like structures around unmagnetised planets: 2. Venus as observed by the Venus Express spacecraft, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-1532, https://doi.org/10.5194/egusphere-egu23-1532, 2023.
The dynamics of finite-size plasma irregularities/jets streaming across magnetic discontinuity regions, as the magnetopause, is a key process for better understanding the transport of mass, momentum and energy from the solar wind towards planetary magnetospheres. In this paper we investigate the kinetic effects and their role on the entry and transport of localized solar wind/magnetosheath plasma structures inside the Hermean magnetosphere under northward orientation of the interplanetary magnetic field. For this purpose, we use three-dimensional particle-in-cell simulations adapted to the interaction between plasma elements/irregularities/jets of finite spatial extent and the typical magnetic field of Mercury’s magnetosphere. Our simulations reveal the penetration of solar wind plasma across the Hermean magnetopause and transport inside the magnetosphere. The entry process is controlled by the magnetic field increase at the magnetopause. For reduced jumps of the magnetic field (i.e. for larger values of the interplanetary magnetic field), the magnetospheric penetration is enhanced. The equatorial dynamics of the plasma element is characterized by a dawn-to-dusk asymmetry, the braking being stronger in the dawn flank. More plasma penetrates into the dusk flank and advances deeper inside the magnetosphere than in the dawn flank. The simulation results are discussed in the context of the impulsive penetration mechanism.
How to cite: Voitcu, G., Echim, M., Teodorescu, E., and Munteanu, C.: Kinetic effects and their role on the entry and transport of finite-size plasma jets inside the Hermean magnetosphere, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12611, https://doi.org/10.5194/egusphere-egu23-12611, 2023.
The interaction between the solar wind and Earth’s magnetic field results in the formation of a supercritical bow shock. Downstream of this shock wave, the magnetosheath region emerges, in which high-speed plasma flows can be formed. These jets have been connected to several shock and foreshock properties. Moreover, due to their unique properties (i.e., higher density and velocity compared to the ambient flow), they can cause a variety of different phenomena, including magnetopause reconnection, excitation of ULF waves and electron acceleration.
In this work, we use Magnetosphere Multiscale (MMS) mission to demonstrate jets’ complex structure by investigating their velocity distribution functions. Specifically, we focus on how their VDFs change over time and on whether they exhibit non-Maxwellian properties. By comparing with the VDFs taken from the background magnetosheath, we show that full particle plasma moments provide an inadequate description of jet plasma properties. Furthermore, we present different metrics to quantify the non-Maxwellian features exhibited by jet observations. Finally, we discuss how the observed kinetic properties of jets may provide insight into jets generation, wave excitation and evolution.
How to cite: Raptis, S., Karlsson, T., Vaivads, A., Lindberg, M., and Trollvik, H.: Velocity distribution functions and non‐Maxwellianity of magnetosheath jets using MMS, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-929, https://doi.org/10.5194/egusphere-egu23-929, 2023.
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 (BS). Using measurements by the Magnetospheric Multiscale (MMS) spacecraft, Goncharov et al. (2020) showed similarities in the plasma properties of the jets and fast plasmoids. However, 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. On the other hand, structures registered close to the BS/magnetopause or in the sub-solar/flank magnetosheath are not fully the same. 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., Šafránková, J., Němeček, Z., and Xirogiannopoulou, N.: Jet-like structures in different regions of the magnetosheath, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3155, https://doi.org/10.5194/egusphere-egu23-3155, 2023.
Magnetosheath jets are a class of phenomena that are usually defined as structures of enhanced dynamic pressure in the magnetosheath. The origins of some jets have been traced back to steepening ULF waves in the foreshock, but other formation mechanisms have also been described. In this study we use four 2D simulation runs of the global magnetospheric hybrid-Vlasov simulation Vlasiator to investigate the formation of magnetosheath jets at the bow shock. We use 2D views of the simulation and virtual spacecraft to investigate the plasma and magnetic field properties around and at the times and locations of jet formation. We find that of the 796 jets analysed this way, 91% appear to form in association with foreshock structures of enhanced dynamic pressure impacting the bow shock. These jets mainly form downstream of the ULF foreshock, while the remaining 9% are generally found near the ULF foreshock edges toward the flanks and have different properties from the foreshock structure-associated jets.
How to cite: Suni, J., Palmroth, M., Battarbee, M., Turc, L., Alho, M., Cozzani, G., Dubart, M., Ganse, U., George, H., Gordeev, E., Grandin, M., Horaites, K., Papadakis, K., Pfau-Kempf, Y., Tarvus, V., Tesema, F., Zaitsev, I., and Zhou, H.: Study of the Local Bow Shock Environment during Magnetosheath Jet Formation: Vlasiator Results, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-1222, https://doi.org/10.5194/egusphere-egu23-1222, 2023.
The turbulent foreshock region upstream of the quasi- parallel bow shock is dominated by waves and reflected particles that interact with each other and create a large number of different foreshock phenomena. The plasma structures with the enhanced magnetic field (Short Large Amplitude Magnetic Structures, SLAMS), and density spikes, named plasmoids, are frequently observed. They are one of the suggested sources of transient flux enhancements (TFE) or jets in the magnetosheath. Using measurements of the Magnetospheric Multiscale Spacecraft (MMS) and OMNI solar wind database between 2015 and 2018 years, we have found that there is a category of events exhibiting both magnetic field and density enhancements simultaneously and we introduce the term “mixed structure” for them. Consequently, we divided our set of observations into three groups and present a comparative statistical analysis in the subsolar foreshock. Based on our results and previous research, we discuss their properties, possible origin, occurrence rate under different upstream conditions and their relation to the jets and plasmoids in the magnetosheath. We suggest that plasmoids and SLAMS are different phenomena created in the foreshock under different upstream conditions and that the enhanced density, rather than magnetic field magnitude, is principal for creation of magnetosheath jets.
How to cite: Xirogiannopoulou, N., Goncharov, O., Šafránková, J., and Němeček, Z.: Characteristics of foreshock subsolar compressive structures and their connection to magnetosheath jet-like phenomena, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3199, https://doi.org/10.5194/egusphere-egu23-3199, 2023.
Linear magnetic holes (LMH) are magnetic field depressions in the solar wind found everywhere in the heliosphere and sometimes downstream of planetary bow shocks. LMH, with only very little rotation of the magnetic field B across the structure, are often considered as the evolutionary endpoint of mirror modes, thus retaining certain characteristics of their parent structure: embedded in a plasma with large temperature anisotropy, large plasma beta, anticorrelation between B and the plasma density. One question is how and under which conditions these large depressions may survive a shock crossing, as observations have recently shown that such a crossing is possible. In other words: what is the interaction between two nonlinear space plasma structures that both scale as the ion gyroradius? To answer this question, we present here the first hybrid simulations of the evolution of a LMH crossing the bow shock boundary of a medium-activity comet using the hybrid Particle-In-Cell (PIC) model Menura. We first create a LMH with mirror mode characteristics in the pristine solar wind and, then, convect it down toward a comet, through the shock, into the cometary magnetosheath. We study its morphology along its path, and how the magnetosheath is impacted locally and as a whole. This work also aims at preparing fundamental space plasma physics aspects of the upcoming multi-spacecraft Comet Interceptor mission.
How to cite: Henri, P., Simon Wedlund, C., Pucci, F., Behar, E., and Ballerini, G.: How do magnetic holes cross a bow shock? Results from the kinetic hybrid plasma model Menura, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6972, https://doi.org/10.5194/egusphere-egu23-6972, 2023.
The foreshock is a turbulent region in front of the quasi-parallel bow shock. The reflected particles from the bow shock and interaction with oncoming waves in the solar wind create it. The foreshock is usually located at the dawn side. However, the foreshock region is relocate to the nose of the bow shock and covers all the dayside magnetospheric system when IMF points to radial or anti-radial directions. This change creates many unusual phenomena in the magnetospheric system, such as the magnetopause expansion, and generates the foreshock transients, such as spontaneous Hot Flow Anomalies (sHFA). Previous studies revealed that foreshock transients are preferred to occur under a radial IMF condition, however, what is the reason for this preference is still unclear. Using THEMIS and MMS data, the analysis presents a statistical analysis to reveal the foreshock characteristics under the radial IMF to check the reasons for the preference of foreshock transients. The primary solar wind parameters in the foreshock and/or solar wind under these conditions are revealed. The ULF wave behavior is also taken account.
How to cite: Pi, G., Salohub, A., Xirogiannopoulou, N., Němeček, Z., and Šafránková, J.: A Statistical Study of Foreshock Environment under Radial IMF Conditions, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-8347, https://doi.org/10.5194/egusphere-egu23-8347, 2023.
Far from an ideal laminar flow, the solar wind impacting planetary magnetospheres contains a spectrum of fluctuations extending to virtually all scales. The study of the effects of such fluctuations on a magnetosphere was until recently lacking a numerical tool which would provide a self-consistent global picture of such an interaction. Using a novel 2-step approach, the open source, hybrid-PIC code Menura is employed to first develop a 3D turbulent cascade in an otherwise homogeneous plasma, to then inject this turbulent solution in a domain containing a permanent dipole. We show how solar wind turbulence is affected by the crossing of the shock, and conversely how the global shape of the magnetosphere is evolving compared to its laminar counterpart. We additionally highlight how transient phenomena and coherent structures are naturally occurring in the foreshock and the sheath due to the local direction of the turbulent magnetic field.
How to cite: Behar, E., Henri, P., Ballerini, G., Pucci, F., and Simon-Wedlund, C.: Global 3D simulation of the interaction between a turbulent solar wind and a magnetic dipole, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12129, https://doi.org/10.5194/egusphere-egu23-12129, 2023.
Magnetic holes (MHs) are deep depressions in the magnetic field found in the solar wind and in planetary magnetosheaths. Based on Cluster multi-point data from the pristine solar wind, we investigate the morphology of MHs exhibiting no to little rotation in the magnetic field (linear MHs). We introduce a new coordinate system, to better see the variation in the structure, and to be able to connect to solenoid-based models. We will present two events; One is an event where the observations suggest a long cylindrical shape, where the observations are compared to an infinitely long solenoid model. For this event we only consider a 2D model. The other event is where the observations suggest a truncated cylinder shape, where the event is compared to a 3D model of a truncated solenoid. We will show how well the models are able to reconstruct the observations and present some results.
How to cite: Trollvik, H., Karlsson, T., and Raptis, S.: Morphology case study of magnetic holes in the pristine solar wind, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15140, https://doi.org/10.5194/egusphere-egu23-15140, 2023.
We have investigated approximately four years of MESSENGER data to identify short, large-amplitude magnetic structures (SLAMS) in the Mercury foreshock. Defining SLAMS as well-defined structures with a magnetic field strength of at least a factor of 3 higher than the background magnetic field, when MESSENGER is located in the solar wind, we find 435 SLAMS. The SLAMS are found either in regions of a general ultra-low frequency (ULF) wave field, at the boundary of such a ULF wave field, or isolated from the wave field. We invetigate several properties of the SLAMS, such as temporal scale size, amplitude, and polarization. We find that SLAMS are mostly found during periods of low interplanetary magnetic field strength, indicating that they are more common for higher solar wind Alfvénic Mach number (MA). We use the Tao solar wind model to estimate solar wind parameters to verify that MA is indeed larger during SLAMS observations than otherwise. Finally, we also investigate how SLAMS observations are related to foreshock geometry.
How to cite: Karlsson, T. and Plaschke, F.: MESSENGER observations of short, large-amplitude magnetic structures (SLAMS) in the Mercury foreshock, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-2702, https://doi.org/10.5194/egusphere-egu23-2702, 2023.
Magnetic holes are significant depressions of the interplanetary magnetic field (IMF) that can be found embedded in the solar wind everywhere within the heliosphere. They resemble mirror mode magnetic structures that form as a response to excess perpendicular temperatures. Magnetic holes situated at IMF discontinuities (current sheets) may also be the result of reconnection. Magnetic holes occur more often under fast solar wind conditions, and their scale sizes are known to be on the order of thousands to tens of thousands of km, determined essentially from temporal width and plasma velocity observations. So far, the scale sizes have only been estimated for the directions parallel to the respective solar wind plasma flows. In this study, we attempt to calculate the first distributions of the scale sizes for the orthogonal, flow-perpendicular directions. Therefore, we use multi-point observations of magnetic holes by the ARTEMIS spacecraft in lunar orbit. The method we use has been previously applied to plasma jets present in the magnetosheath of Earth. The knowledge of the flow-perpendicular scale sizes is important to assess the holes’ impact on planetary magnetospheres and cometary environments.
How to cite: Plaschke, F., Volwerk, M., Karlsson, T., Götz, C., Heyner, D., Hietala, H., Mieth, J. Z. D., Schmid, D., Simon-Wedlund, C., and Vörös, Z.: On the scale sizes of magnetic holes, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4366, https://doi.org/10.5194/egusphere-egu23-4366, 2023.
Posters virtual: Fri, 28 Apr, 10:45–12:30 | vHall ST/PS
The shock wave is a primary interface for plasma heating and charged particle acceleration. In collisionless solar wind plasma, such acceleration is attributed to the wave-particle resonant interactions. This letter focuses on electron acceleration by one of the most widespread high-frequency electromagnetic wave emissions, whistler-mode waves. Using spacecraft observations of the Earth's foreshock transient, we demonstrate that intense whistler-mode waves may resonate nonlinearly with $\sim 10-100$eV solar wind electrons and accelerate them to $\sim 100-500$eV. Accelerated electron population has a butterfly pitch-angle distribution, in agreement with theoretical predictions. The presented evidence of the efficiency of nonlinear resonant acceleration suggests that this mechanism may play an important role in solar wind electron injection into the shock-drift acceleration.
How to cite: Shi, X., Artemyev, A., Angelopoulos, V., Liu, T., and Zhang, X.-J.: Electron acceleration by intense whistler-mode waves at foreshock transients, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-2963, https://doi.org/10.5194/egusphere-egu23-2963, 2023.
