Foreshock Properties at Typical and Enhanced Interplanetary Magnetic Field Strengths: Results From Hybrid‐Vlasov Simulations

Turc, Lucile; Ganse, Urs; Pfau‐Kempf, Yann; Hoilijoki, Sanni; Battarbee, Markus; Juusola, Liisa; Järvinen, R.; Brito, Thiago; Grandin, Maxime; Palmroth, Minna

doi:10.1029/2018ja025466

Cited by 37 publications

(58 citation statements)

References 65 publications

(127 reference statements)

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“…Atypical ion VDFs are observed in conjunction with the unusual wave activity. During one event, we find clear evidence of two distinct FABs in cyclotron resonance with the waves observed shortly afterward, consistent with previous numerical works (Turc et al, ). In another, the FAB is accompanied by a second suprathermal population at nonzero pitch angle, which might have evolved from a second FAB, due to gyrophase trapping (Mazelle et al, ; Kempf et al, ).…”

Section: Discussionsupporting

confidence: 92%

First Observations of the Disruption of the Earth's Foreshock Wave Field During Magnetic Clouds

Turc

Roberts

Archer

et al. 2019

Geophysical Research Letters

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The foreshock, extending upstream of Earth's bow shock, is a region of intense electromagnetic wave activity and nonlinear phenomena, which can have global effects on geospace. It is also the first geophysical region encountered by solar wind disturbances journeying toward Earth. Here, we present the first observations of considerable modifications of the foreshock wave field during extreme events of solar origin called magnetic clouds. Cluster's multispacecraft data reveal that the typical quasi‐monochromatic foreshock waves can be completely replaced by a superposition of waves each with shorter correlation lengths. Global numerical simulations further confirm that the foreshock wave field is more intricate and organized at smaller scales. Ion measurements suggest that changes in shock‐reflected particle properties may cause these modifications of the wave field. This state of the foreshock is encountered only during extreme events at Earth, but intense magnetic fields are typical close to the Sun or other stars.

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Section: Discussionsupporting

confidence: 92%

First Observations of the Disruption of the Earth's Foreshock Wave Field During Magnetic Clouds

Turc

Roberts

Archer

et al. 2019

Geophysical Research Letters

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“…This effect may be caused by the differing scales of foreshock structures, with S2 foreshock dynamics causing clumped enhancements of reflected particles in the vicinity of the shock, and the strong ULF and SLAMS signatures in S1 causing corresponding rarefications as well as enhancements. This phenomenon was investigated in Turc et al (2018), as shown in their Figure 2, panels b through d.…”

Section: Test-particle Resultsmentioning

confidence: 96%

“…Vlasiator is capable of modeling a number of ion kinetic effects even without resolving ion kinetic scales spatially (Pfau-Kempf et al, 2018), and has been used for a number of interesting foreshock and bow shock studies (Palmroth et al, 2015;Pfau-Kempf et al, 2016;Turc et al, 2018;Blanco-Cano et al, 2018) In this paper, we use two datasets (simulations S1 and S2) modeling two different bow shock strengths and interplanetary magnetic field intensities. Results from these simulations have previously been published in Palmroth et al (2015) and Turc et al (2018). They are ecliptic plane (x − y) 2D-3V simulations (2D in the spatial domain, 3D in the velocity domain) parametrized using the GSE coordinate system with no tilt for the Earth's dipole.…”

Section: Vlasiator Simulationmentioning

confidence: 99%

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Non-locality of the Earth's quasi-parallel bow shock: injection of thermal protons in a hybrid-Vlasov simulation

Battarbee¹,

Ganse²,

Pfau‐Kempf³

et al. 2019

Preprint

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Abstract. We study the interaction of solar wind protons with the Earth's quasi-parallel bow shock using a hybrid-Vlasov simulation. We employ the high-fidelity global hybrid model Vlasiator to include effects due to bow shock curvature, tenuous upstream populations, and foreshock waves. We investigate the local uncertainty of the position of the quasi-parallel bow shock as a function of several plasma properties, and find that for a significant portion of time, the local bow shock position is challenging to define. Our results support the notion of upstream structures causing patchwork reconstruction of the quasi-parallel shock front in a non-uniform manner. We propose a novel method for spacecraft data to be used to analyze this quasi-parallel reformation. We combine our hybrid-Vlasov results with test-particle studies and show that shock non-locality appears to have little direct efficient on particle injection. We show that proton energization, which is required for injection, takes place throughout a larger shock transition zone. Non-local energization of particles is found regardless of the instantaneous non-locality of the shock front. Distortion of magnetic fields in front of and at the shock is shown to have a significant effect on proton injection. We additionally show that the density of suprathermal reflected particles upstream of the shock may not be a useful metric for the probability of injection at the shock, as foreshock dynamics and particle trapping appear to have a greater effect on energetic particle accumulation at a given position in space. Our results have significant implications for statistical and spacecraft studies of the shock injection problem.

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“…the Sun-Earth line in Run 2B. This could be related to foreshock disturbances being weaker at lower M A , since the density of suprathermal ions is reduced (Turc et al, 2015(Turc et al, , 2018.…”

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confidence: 92%

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

Turc¹,

Tarvus²,

Dimmock³

et al. 2020

Preprint

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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 accurately the polarity of the asymmetries, 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. We investigate how the asymmetries change when the angle between the IMF and the Sun-Earth line is reduced and when the Alfven 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 Alfven Mach number leads to a reduced magnetic field asymmetry and a decrease in the variability of the magnetosheath density and velocity, the latter likely due to weaker foreshock processes. Our results highlight the strong impact of the foreshock on global magnetosheath properties, in particular on the magnetosheath density, which is extremely sensitive to transient foreshock processes.

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Foreshock Properties at Typical and Enhanced Interplanetary Magnetic Field Strengths: Results From Hybrid‐Vlasov Simulations

Cited by 37 publications

References 65 publications

First Observations of the Disruption of the Earth's Foreshock Wave Field During Magnetic Clouds

First Observations of the Disruption of the Earth's Foreshock Wave Field During Magnetic Clouds

Non-locality of the Earth's quasi-parallel bow shock: injection of thermal protons in a hybrid-Vlasov simulation

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

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