Terrestrial Magnetosheath Research Articles

Solar Wind Charge-Exchange X-ray Emissions from the O5+ Ions in the Earth’s Magnetosheath

The spectra and global distributions of the X-ray emissions generated by the solar wind charge-exchange (SWCX) process in the terrestrial magnetosheath are investigated based on a global hybrid model and a global geocoronal hydrogen model. Solar wind O6+ ions, which are the primary charge state for oxygen ions in solar wind, are considered. The line emissivity of the charge-exchange-borne O5+ ions is calculated by the Spectral Analysis System for Astrophysical and Laboratory (SASAL). It is found that the emission lines from O5+ range from 105.607 to 118.291 eV with a strong line at 107.047 eV. We then simulate the magnetosheath X-ray emission intensity distributions with a virtual camera at two positions of the north pole and dusk at six stages during the passing of a perpendicular interplanetary shock combined with a tangential discontinuity structure through the Earth’s magnetosphere. During this process, the X-ray emission intensity increases with time, and the maximum value is 27.11 keV cm−2 s−1 sr−1 on the dayside, which is 4.5 times that before the solar wind structure reached the Earth. A clear shock structure can be seen in the magnetosheath and moves earthward. The maximum emission intensity seen at dusk is always higher than that seen at the north pole.

Effects of Electron Vortices on the Magnetic Structures in the Terrestrial Magnetosheath

AbstractElectron vortices are usually embedded within different magnetic structures in space plasmas. The effects, including the nonideal electric field, energy dissipation and magnetic field, of electron vortices on these magnetic structures are still unclear. Utilizing the unprecedented high‐resolution data from the Magnetospheric Multiscale mission in the terrestrial magnetosheath, we statistically investigate these effects on magnetic structures. Both nonideal electric fields and energy dissipation have no obvious correlations with the scales of electron vortices. However, compared to the scales, stronger correlations are found between the vorticities of electron vortices and nonideal electric fields, and energy dissipation, respectively. Most of electron vortices have positive contributions to magnetic fields of magnetic structures, such as strengthening the decrease (or increase) of Bt for current sheets and magnetic holes (or flux ropes and magnetic peaks). Our results reveal that the electron vortices play an important role in the evolution of magnetic structures.

Statistical Characteristics of Electron Vortexes in the Terrestrial Magnetosheath

Utilizing the unprecedented high-resolution Magnetospheric Multiscale mission data from 2015 September to 2017 December, we perform a statistical study of electron vortexes in the turbulent terrestrial magnetosheath. On the whole, 506 electron vortex events are successfully selected. Electron vortexes can occur at four known types of magnetic structures, including 78, 42, 26, and 39 electron vortexes observed during the crossings of the current sheets, magnetic holes, magnetic peaks, and flux ropes, respectively. Except for the four types of structures, the rest of the electron vortexes are in the “Others” category, defined as unknown structures. The electron vortexes mainly occur in the subsolar region, with only a few in the flank region. The total occurrence rate of all electron vortexes is 4.86 hr–1, with, on average, 3.65 events hr−1 in the X-Y plane and 3.26 events hr−1 in the X-Z plane. The durations of most of the electron vortexes concentrate within 0.5–1.5 s and are 1.09 s on average. The electron vortexes are ion-scale structures owing to the average scale of 2.05 ion gyroradius. In addition, the means, medians, and maxima of the energy dissipation J · E′ in the electron vortexes are almost positive, implying that the electron vortex may be a potential coherent structure or channel for turbulent energy dissipation. All these results reveal the statistical characteristics of electron vortexes in the magnetosheath and improve our understanding of energy dissipation in astrophysical and space plasmas.

Magnetosheath Jet Formation Influenced by Parameters in Solar Wind Structures.

Magnetosheath jets are dynamic pressure enhancements observed in the terrestrial magnetosheath. Their generation mechanisms are currently debated but the majority of jets can be linked to foreshock processes. Recent results showed that jets are less numerous when coronal mass ejections (CMEs) cross the magnetosheath and more numerous when stream interaction regions (SIRs) cross it. Here, we show for the first time how the pronounced substructures of CMEs and SIRs are related to jet production. We distinguish between compression and magnetic ejecta (ME) regions for the CME as well as compression region associated with the stream interface and high-speed streams (HSSs) for the SIR. Based on THEMIS and OMNI data covering 2008-2021, we show the 2D probability distribution of jet occurrence using the cone angle and Alfvén Mach number. We compare this distribution with the values within each solar wind (SW) structure. We find that both high cone angles and low Alfvén Mach numbers within CME-MEs are unfavorable for jet production as they may inhibit a well-defined foreshock region. 1D histograms of all parameters show, which SW parameters govern jet occurrence in each SW structure. In terms of the considered parameters the most favorable conditions for jet generation are found for HSSs due to their associated low cone angles, low densities, and low magnetic field strengths.

Kinetic Simulations of Proton Mirror Instability: Phase Relations and Thermodynamics

Mirror-mode waves driven by the large temperature anisotropy of T ⊥/T ∣∣ > 1 have been widely observed in the solar wind, planetary magnetosheaths, heliosheath, etc. Recent studies have shown that the phase relations and thermodynamics of the mirror waves observed in the terrestrial magnetosheath may well be interpreted by the linear mixed kinetic–MHD theory of proton mirror instability. In particular, the energy laws possess the form of double-polytropic closures with the thermodynamic exponents being functions of β ⊥,∣∣ = p ⊥,∣∣/(B 2/2μ 0). In this study, we examine the time evolution of proton mirror instability based on the hybrid particle simulations for twenty sets of β ⊥,∣∣ values. Quantitative comparisons between the kinetic simulations, linear Vlasov theory, and observations are made in terms of the growth rates, phase relations, thermodynamic conditions, etc., which show high agreements. In particular, the dependences of various compressibility and thermodynamic exponents on β ⊥,∣∣ are confirmed by the kinetic simulations, which show that the polytropic exponents are in the ranges of γ ⊥ = 0.64 ± 0.21, and γ ∣∣ = 1.07 ± 0.12 consistent with the theoretical predictions and mirror observations of γ ⊥ < 1 and γ ∣∣ ≳ 1. It is shown that the observed features, including the various perturbations and wavelengths, may indeed be reproduced by the nonlinear simulations. The saturated temperature anisotropy β ⊥/β ∣∣ and plasma β ∣∣ show an anticorrelation, which may well be fitted by the modified mirror instability threshold of with γ ⊥ ≈ 0.8, γ ∣∣ ≈ 1.3, and the saturated magnetic field of δ B/B ≈ 0.26 ∼ 0.97 increases with increasing values of β ≈ 1.6 ∼ 8.3.

Detecting Discontinuities From In Situ Space Measurements: Method and FPGA Implementation

AbstractThe analysis in real time of space data variability is essential for scientists and space mission controllers. Automated tools designed to extract key descriptors of variability are needed and solutions to adapt such algorithms for on‐board computers are rare. This paper describes the design of an automated system for detecting directional discontinuities of a physical quantity and its implementation in Field‐Programmable Gate Array (FPGA). The system is currently adapted for solar wind or terrestrial magnetosheath magnetic field directional discontinuities, that is, sharp changes of the magnetic field directionality. Our detection algorithm uses analysis windows of adjustable width and averaging procedures in order to reduce the effects of random fluctuations. A sliding‐window approach is designed for continuous monitoring and detection of magnetic directional discontinuities. A software implementation of the algorithm was tested using in‐situ magnetic field measurements, and emphasized improvements of performance when using analysis windows of adjustable width. The FPGA implementation of the detection algorithm is built on DILIGENT Nexys 4 DDR featuring a commercial Xilinx Artix‐7 device and is designed to be ported to space qualified infrastructure. The FPGA system was tested with synthetic and laboratory signals, and provides results in very good agreement with the software implementation. The FPGA system provides an efficient real‐time monitoring solution using minimal computational and energy resources, and reducing the main on‐board computer utilization.

Electron-scale Magnetic Peaks Upstream of Mercury’s Bow Shock: MESSENGER Observations

Electron-scale magnetic peaks (ESMPs) with spatial sizes less than one local ion gyroradius have been recently revealed to exist in the terrestrial magnetosheath and solar wind at 1 au. Whether they widely exist in the astrophysical plasma is unclear. Here, we investigate the magnetic peaks with a period of 0.1–100 s upstream of Mercury’s bow shock by using the magnetic field data from the MESSENGER spacecraft. Based on the distribution of their durations, these magnetic peaks can be divided into two groups: one with durations less than 0.6 s and the other with durations larger than 0.6 s. The durations in each group obey a log-normal distribution. The magnetic peaks with durations less than 0.6 s are inferred to be electron scale, suggesting that ESMPs exist in the solar wind at Mercury’s orbit. The median duration of these ESMPs is ∼0.3 s. The ESMPs have a larger occurrence rate near the bow shock and prefer to occur when the ambient interplanetary magnetic field (IMF) can be connected to the bow shock, which suggests that the foreshock could be one source region of these ESMPs. Their occurrence rate also tends to be larger when the IMF strength is weaker. Our observations also suggest that some ESMPs originate from the upstream solar wind. The properties of the ESMPs found here could help to shed light on their generation mechanisms and their roles in the astrophysical plasma.

Study of the Electron‐Scale Magnetic Peaks in the Magnetotail Current Sheet Observed by the Magnetospheric Multiscale Mission

AbstractElectron‐scale magnetic holes have been revealed to widely exist in many plasma environments in the last decade, playing an important role in transporting particles and dissipating energies. Recently, electron‐scale magnetic peaks (ESMPs) have also been reported to exist in the terrestrial magnetosheath and the solar wind at 1 AU. Here, we report the existence of ESMPs in the terrestrial magnetotail current sheet for the first time based on observations of the Magnetospheric Multiscale (MMS) mission. We find a clear bipolar signature in the electron velocity inside one ESMP, suggesting the existence of an electron vortex inside it. The current in the ESMP is mainly contributed by electrons. We also find that they prefer to occur near the neutral sheet with a northward component of the magnetic field, suggesting that they prefer to occur during the dipolarization process. Our observation results suggest that both ion and electron mirror instabilities are not the generation mechanism of these ESMPs. Their role and generation mechanism in the magnetotail current sheet are unclear and need further investigation.

Comparing Quasi-Parallel and Quasi-Perpendicular Configuration in the Terrestrial Magnetosheath: Multifractal Analysis

The terrestrial magnetosheath is characterized by large-amplitude magnetic field fluctuations. In some regions, and depending on the bow-shock geometry, these can be observed on several scales, and show the typical signatures of magnetohydrodynamic turbulence. Using Cluster data, magnetic field spectra and flatness are observed in two intervals separated by a sharp transition from quasi-parallel to quasi-perpendicular magnetic field with respect to the bow-shock normal. The multifractal generalized dimensions Dq and the corresponding multifractal spectrum f(α) were estimated using a coarse-graining method. A p-model fit was used to obtain a single parameter to describe quantitatively the strength of multifractality and intermittency. Results show a clear transition and sharp differences in the intermittency properties for the two regions, with the quasi-parallel turbulence being more intermittent.

Statistical Analysis of the Distribution and Evolution of Mirror Structures in the Martian Magnetosheath

The mirror-mode structures in the Martian magnetosheath that were observed by Mars Atmosphere and Volatile Evolution during 2015–2018 are analyzed statistically. It is found that most mirror-mode events occurred close to the bow shock. Morphological categorization based on skewness of the magnetic field shows that ∼46.57% of the observed mirror-mode events are peak-like, ∼40.25% are wave-like, and ∼13.18% are dip-like. The mirror-mode structures mostly saturate in a very short time after their formation near the bow shock, which is a result of the high temperature anisotropy and high plasma beta at this location. Carried downstream by the magnetosheath flow, the mirror-mode structures remain in nonlinear saturation states. Meanwhile, the dayside magnetosheath plasma largely deviates from marginal stability, which is a state commonly that is expected in the terrestrial magnetosheath. By flowline tracing in an MHD model, it is found the mirror structures can be divided into two groups: ∼80% of the events that are observed near the bow shock evolve less than 10 s in plasma with high temperature anisotropy and high plasma beta value, keeping in saturated states; the other 20% of the events evolve following a similar process to that at the Earth, undergoing morphology transition in response to the local plasma conditions. However, the dayside magnetosheath is largely in an unstable condition, which prevents the mirror-mode structures from fully evolving into the decaying phase. Our results suggest that energy dispassion through wave-particle interaction might not be sufficient to remove the free energy that is introduced by the solar wind–Mars interaction.

High-precision Calibration of the Fluxgate Magnetometer Offset Vector in the Terrestrial Magnetosheath

High-precision magnetic field measurements are of great significance for the in-depth study of the physical processes in the astrophysical plasma environment. To obtain accurate natural magnetic fields, in-flight calibration is one key step to obtaining zero offset of the spaceborne fluxgate magnetometer (FGM). Mirror mode structures, widely existing in the solar wind and planetary magnetosheaths and magnetospheres, can be used to calculate the zero offset. However, it is difficult to obtain an accurate zero offset by the current methods using mirror mode structures in the planetary magnetosheath. Here, we develop a new method to calculate the zero offset of the spaceborne FGM using magnetic dips, which are a kind of mirror mode structure. This method is based on the assumption that the magnetic field is zero in the cross section of the magnetic dip. Our method is able to calculate the zero offset using only one magnetic dip. We test this method by using the data from the Magnetospheric Multiscale Mission, and find that the calculation errors of 78.1% of the estimated zero offsets are <0.5 nT when using 25 magnetic dips in the terrestrial magnetosheath. This suggests that our method is able to achieve a high accuracy of the zero offset in the planetary magnetosheath.

A Statistical Study of the Moon's Magnetotail Plasma Environment

AbstractThis study investigates the lunar plasma environment when embedded within Earth's magnetotail. We use data from 10 years of tail crossings by the Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) spacecraft in orbit around the Moon. We separate the plasma environments by magnetosheath‐like, magnetotail lobe‐like, and plasma sheet‐like conditions. Our findings highlight that the lobe‐like plasma is associated with low densities and a strong magnetic field, while the plasma sheet is characterized by higher densities and a weaker magnetic field. These regions are flanked by the fast, predominantly tailward flows of the terrestrial magnetosheath. During a single lunar crossing, however, the magnetotail displays a wide range of variability, with transient features—including reconnection events—intermixed between periods of lobe‐like or sheet‐like conditions. We compare and contrast the Moon's local magnetotail plasma to the environments near various outer‐planet moons. In doing so, we find that properties of the ambient lunar plasma are, at times, unique to the terrestrial magnetotail, while at others, may resemble those near the Jovian, Saturnian, and Neptunian moons. These findings highlight the complementary role of the ARTEMIS mission in providing a deeper understanding of the plasma interactions of the outer‐planet moons.

Statistical Study of Small-scale Magnetic Holes in the Upstream Regime of the Martian Bow Shock

Abstract Small-scale magnetic holes (SSMHs) are frequently observed in the solar wind at 1 au, as well as the terrestrial current sheet and magnetosheath. These kinetic-size structures play an important role in energy dissipation and particle transportation. Here, we report the existence of SSMHs in the upstream regime of the Martian bow shock and statistically investigate these SSMHs based on 5 yr observations of the Mars Atmosphere and Volatile EvolutioN spacecraft. A total of 549 SSMHs are found, and their durations and sizes obey the lognormal distribution. The median duration is ∼0.46 s, and the median size is ∼2 ion inertial lengths. We regard an isolated SSMH or a train of SSMHs as a SSMH event. The average occurrence rate of the SSMH events is ∼0.6 event per day. The occurrence rate is much larger in the region belonging to the ion foreshock on average, suggesting that the ion foreshock is an important source of SSMHs. The occurrence of the SSMH events tends to be larger when the ion number density and the interplanetary magnetic field (IMF) strength are larger, indicating that the generation of SSMHs might be associated with ions and the IMF strength. Although their generation mechanism is still unclear, the finding of the link between the occurrence rate of the SSMH events and ion number density, as well as the IMF strength, might provide a clue to further reveal the generation mechanism of SSMHs in the solar wind or planetary foreshock.

A Possible Link between Turbulence and Plasma Heating

Abstract Numerical simulations and experimental results have shown that the formation of current sheets in space plasmas can be associated with enhanced vorticity. Also, in simulations the generation of such structures is associated with strong plasma heating. Here, we compare four-point measurements in the terrestrial magnetosheath turbulence from the Magnetospheric Multiscale mission of the flow vorticity and the magnetic field curlometer versus their corresponding one-point proxies PVI(V) and PVI(B) based on the Partial Variance of Increments (PVI) method. We show that the one-point proxies are sufficiently precise in identifying not only the generic features of the current sheets and vortices statistically, but also their appearance in groups associated with plasma heating. The method has been further applied to the region of the turbulent sheath of an interplanetary coronal mass ejection (ICME) observed at L1 by the WIND spacecraft. We observe current sheets and vorticity associated heating in larger groups (blobs), which so far have not been considered in the literature on turbulent data analysis. The blobs represent extended spatial regions of activity with enhanced regional correlations between the occurrence of conditioned currents and vorticity, which at the same time are also correlated with enhanced temperatures. This heating mechanism is substantially different from the plasma heating in the vicinity of the ICME shock, where plasma beta is strongly fluctuating and there is no vorticity. The proposed method describes a new pathway for linking the plasma heating and plasma turbulence, and it is relevant to in situ observations when only single spacecraft measurements are available.

Nature of Electrostatic Fluctuations in the Terrestrial Magnetosheath

Abstract The high cadence plasma, electric, and magnetic field measurements by the Magnetospheric MultiScale spacecraft allow us to explore the near-Earth space plasma with an unprecedented time and spatial resolution, resolving electron-scale structures that naturally emerge from plasma complex dynamics. The formation of small-scale turbulent features is often associated to structured, non-Maxwellian particle velocity distribution functions that are not at thermodynamic equilibrium. Using measurements in the terrestrial magnetosheath, this study focuses on regions presenting bumps in the power spectral density of the parallel electric field at subproton scales. Correspondingly, it is found that the ion velocity distribution functions exhibit beam-like features at nearly the local ion thermal speed. Ion-cyclotron waves in the ion-scale range are frequently observed at the same locations. These observations, supported by numerical simulations, are consistent with the generation of ion-bulk waves that propagate at the ion thermal speed. This represents a new branch of efficient energy transfer at small scales, which may be relevant to weakly collisional astrophysical plasmas.

Bombardment of Lunar Polar Crater Interiors by Out-of-ecliptic Ions: ARTEMIS Observations

Abstract Permanently shadowed regions (PSRs) inside lunar polar craters likely harbor volatiles which are of great interest for both science and resource utilization. The origin and evolution of this resource is in part driven by external space weathering, including the bombardment by space plasma ions. Previous work has investigated the flux of horizontal solar wind ions that are deflected into lunar polar craters by plasma wake electrostatic fields. Here, we constrain the flux of ions that travel northward or southward in the natural environment encountered by the Moon along its orbit. Using 9 years of in situ ion measurements gathered by the ARTEMIS mission, we find that all locations inside lunar craters are altered by a flux of out-of-ecliptic ions of 10−3 times the solar wind flux. In particular, the central floor of Shackleton’s crater is weathered by a non-null ion flux. The origin of northward and southward ions impacting the Moon is identified as (i) shocked thermalized solar wind ions in the terrestrial magnetosheath and (ii) the isotropic component of ion distributions in the terrestrial magnetotail. The energy spectrum of out-of-ecliptic ions is found to be flatter than the solar wind spectrum. Thus, sputtering of pure water ice irradiated by out-of-ecliptic ions would be created for more than 30% by &gt;3 keV protons, unlike equatorial locations that are mostly sputtered by 1 keV protons. Future work may investigate the influence of the low, but nonzero flux of out-of-ecliptic ions reported here on the budget of volatiles in lunar PSRs.

Statistical Survey of Collisionless Dissipation in the Terrestrial Magnetosheath

AbstractKinetic dissipation of turbulence is an important physical process occurring in collisionless plasmas. Using in‐situ data from the Magnetospheric Multiscale (MMS) Mission, we investigate the statistical distribution of kinetic dissipation in the terrestrial magnetosheath. We make use of an analysis of the Vlasov–Maxwell equations that provides a general description of transfer of internal energy, fluid‐flow energy, and electromagnetic energy in collisionless plasma, including both spatial transport and conversion between forms. In particular, we focus on the channels that separately produce proton and electron internal energies. Applying those results to MMS burst‐mode data obtained in the weakly collisional, turbulent magnetosheath plasma, it is possible to quantify contributions to dissipation from the compressive pressure‐dilatation channel, and from the incompressive pressure‐strain channel, for both plasma species. We also employ a simple spatial filtering approach as a first step to quantifying plasma heating at large and small scales. The analysis is carried out for 50 selected turbulent data intervals, and statistical distributions of the results are presented.

Multi‐Spacecraft Measurement of Anisotropic Spatial Correlation Functions at Kinetic Range in the Magnetosheath Turbulence

AbstractWe investigate spatial correlation functions (SCFs) at kinetic range in the terrestrial magnetosheath because of wide angular distributions of the magnetic field fluctuations and the high Signal‐to‐Noise‐Ratio. We employ four‐point measurements of magnetic fluctuations from the Cluster and MMS concerning a spatiotemporally varying background magnetic field to constitute the two‐dimensional (2‐D) SCFs between ion and electron scales. It is found that two populations exist in the 2‐D SCFs, with the minority elongated along the perpendicular coordinate (S⊥) and the majority of population elongated along the coordinate parallel to average magnetic field (S||). This kind of phenomenon indicates that the distribution of magnetosheath turbulence in the wavenumber space is dominantly transverse to the background magnetic field, simultaneously partly along the field (i.e., k⊥ &gt;&gt; k||). In addition, we find that magnetosheath turbulence is the dominance of shear Alfvénic‐like fluctuations, and is quasi‐monofractal intermittent turbulence at kinetic range for both the Cluster case and the MMS case, indicating that strong spatially anisotropic fluctuations may be universal in the magnetosheath. Our observations pose new challenges to the theoretical modeling of turbulence and dissipation at kinetic range in the collisionless magnetized plasma.

Dawn‐Dusk Asymmetry in Energetic (&gt;20 keV) Particles Adjacent to Saturn's Magnetopause

AbstractEnergetic particles (&gt;∼25 keV) have been observed routinely in the terrestrial magnetosheath, but have not been well studied at the magnetosheaths of the outer planets. Here we analyze energetic electrons and ions (mostly protons) in the vicinity (±1 RS) of Saturn's magnetopause, using particle data acquired with the low‐energy magnetosphere measurements system, one of the three sensors of the magnetosphere imaging instrument on board the Cassini spacecraft, during a period of ∼14 years (2004–2017). It is found that energetic particles, especially ions, are also common in Saturn's magnetosheath. A clear inward (toward Saturn) gradient in the electron differential flux is identified, suggestive of magnetospheric sources. Such an inward gradient does not appear in some of the ion channels. We conclude that Saturn's magnetopause acts as a porous barrier for energetic electrons and, to a lesser extent, for energetic ions. A dawn‐dusk asymmetry in the gradient of particle flux across the magnetopause is also identified, with a gradual decrease at the dawn and a sharp decrease at the dusk magnetopause. It is also found that magnetic reconnection enhanced flux levels just outside of the magnetopause, with evidence suggesting that these particles are from magnetospheric sources. These findings strongly suggest that Saturn's magnetosphere is most likely the main source of energetic particles in Saturn's magnetosheath and magnetosphere leakage is an important process responsible for the presence of the energetic particles in Saturn's magnetosheath.

Asymmetries in the Earth's dayside magnetosheath: results from global hybrid-Vlasov simulations

Abstract. Bounded by the bow shock and the magnetopause, the magnetosheath forms the interface between solar wind and magnetospheric plasmas and regulates solar wind–magnetosphere coupling. Previous works have revealed pronounced dawn–dusk asymmetries in the magnetosheath properties. The dependence of these asymmetries on the upstream parameters remains however largely unknown. One of the main sources of these asymmetries is the bow shock configuration, which is typically quasi-parallel on the dawn side and quasi-perpendicular on the dusk side of the terrestrial magnetosheath because of the Parker spiral orientation of the interplanetary magnetic field (IMF) at Earth. Most of these previous studies rely on collections of spacecraft measurements associated with a wide range of upstream conditions which are processed in order to obtain average values of the magnetosheath parameters. In this work, we use a different approach and quantify the magnetosheath asymmetries in global hybrid-Vlasov simulations performed with the Vlasiator model. We concentrate on three parameters: the magnetic field strength, the plasma density, and the flow velocity. We find that the Vlasiator model reproduces the polarity of the asymmetries accurately but that their level tends to be higher than in spacecraft measurements, probably because the magnetosheath parameters are obtained from a single set of upstream conditions in the simulation, making the asymmetries more prominent. A set of three runs with different upstream conditions allows us to investigate for the first time how the asymmetries change when the angle between the IMF and the Sun–Earth line is reduced and when the Alfvén Mach number decreases. We find that a more radial IMF results in a stronger magnetic field asymmetry and a larger variability of the magnetosheath density. In contrast, a lower Alfvén Mach number leads to a reduced magnetic field asymmetry and a decrease in the variability of the magnetosheath density, the latter likely due to weaker foreshock processes. Our results highlight the strong impact of the quasi-parallel shock and its associated foreshock on global magnetosheath properties, in particular on the magnetosheath density, which is extremely sensitive to transient quasi-parallel shock processes, even with the perfectly steady upstream conditions in our simulations. This could explain the large variability of the density asymmetry levels obtained from spacecraft measurements in previous studies.