The Dynamics of Very High Alfvén Mach Number Shocks in Space Plasmas

Sundberg, T.; Burgess, David; Scholer, M.; Masters, A.; Sulaiman, A. H.

doi:10.3847/2041-8213/836/1/l4

Cited by 33 publications

(31 citation statements)

References 36 publications

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“…To subtract the solar wind contribution, we use and interpolate data from the SWIA fine mode designed to track and measure solar wind beam ions at a particular subset of energies and directions (Halekas et al, 2015). Quasiperiodic enhancements in the magnetic field and ion density are seen in panels (a) and (b), with an average period of ∼30 s, comparable to the upstream proton gyroperiod 24.2 s. Similar periodic modulations have been observed upstream of Earth and Saturn, which were attributed to the reformation of the bow shock at high Mach numbers (Sulaiman et al, 2015; Sundberg et al, 2017).…”

Section: Observationssupporting

confidence: 57%

“…Near the shock, the solar wind is slowed down and incident ions undergoing reflection have speeds lower than the pristine solar wind,

false| V false| < false| {boldV}_{up} \cdot \overset{boldn}{true} false|

, which could explain why reflected ions are often inside the dashed ellipse. The reflection may also be nonspecular (Sundberg et al, 2017).…”

Section: Observationsmentioning

confidence: 99%

“…The fundamental physical processes of reformation in collisionless shocks are poorly understood and are far from being settled, in part due to limited in situ measurements of the processes. A few studies have shown evidence of nonstationarity and reformation at the terrestrial (Dimmock et al, 2019; Lefebvre et al, 2009; Lobzin et al, 2007; Mazelle et al, 2010; Sundberg et al, 2017), and planetary bow shocks (Shan et al, 2020; Sulaiman et al, 2015; Tiu et al, 2011). Nonstationarity can also manifest itself in the form of shock ripples formed near the shock overshoot (Johlander et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

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Nonstationary Quasiperpendicular Shock and Ion Reflection at Mars

Madanian

Schwartz

Halekas

et al. 2020

Geophysical Research Letters

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Collisionless shocks in space plasma are regions of heating and acceleration of charged particles and dissipation of kinetic energy. These accelerated particles are the source of electromagnetic emissions from supernova remnants and other astrophysical structures. At high Mach numbers, shocks can be inherently nonstationary and exhibit modulated energy transfer and recurring plasma compression areas in the form of reformation. We use data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft to study reformation of the Martian bow shock, which has a relatively high curvature compared to that at Earth, and the upstream solar wind is often mass loaded with a population of pickup ions. We show evidence of ion reflection effects in reformation of a supercritical quasiperpendicular shock.

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Section: Observationssupporting

confidence: 57%

“…Near the shock, the solar wind is slowed down and incident ions undergoing reflection have speeds lower than the pristine solar wind,

false| V false| < false| {boldV}_{up} \cdot \overset{boldn}{true} false|

, which could explain why reflected ions are often inside the dashed ellipse. The reflection may also be nonspecular (Sundberg et al, 2017).…”

Section: Observationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Nonstationary Quasiperpendicular Shock and Ion Reflection at Mars

Madanian

Schwartz

Halekas

et al. 2020

Geophysical Research Letters

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“…However, three-dimensional (3D) [29], and some two-dimensional (2D) [30,31], particle-in-cell (PIC) simulations of quasiperpendicular high-M A shocks demonstrate strong amplification of the upstream magnetic field due to the ion-ion filamentation/Weibel instability [32,33], which results from the interaction of upstream and shock-reflected ions. The mediation of high-M A shocks by the Weibel instability is also confirmed by laboratory experiments [34] and in situ measurements of the Earth's bow shock at M A ≃ 39 [35]. In this Letter, we discuss a mechanism of magnetic field amplification that is based on a realistic description of perpendicular nonrelativistic high-M A shocks and can explain the correlation between field strength and M A observed with Cassini at Saturn's bow shock.…”

supporting

confidence: 54%

Magnetic Field Amplification by the Weibel Instability at Planetary and Astrophysical Shocks with High Mach Number

Bohdan¹,

Pohl

Niemiec

et al. 2021

Phys. Rev. Lett.

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Collisionless shocks are ubiquitous in the Universe and often associated with a strong magnetic field.Here, we use large-scale particle-in-cell simulations of nonrelativistic perpendicular shocks in the high-Mach-number regime to study the amplification of the magnetic field within shocks. The magnetic field is amplified at the shock transition due to the ion-ion two-stream Weibel instability. The normalized magnetic field strength strongly correlates with the Alfvénic Mach number. Mock spacecraft measurements derived from particle-in-cell simulations are fully consistent with those taken in situ at Saturn's bow shock by the Cassini spacecraft.

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“…Collisionless plasmas support energetic structures that are not captured by a single-fluid MHD theory and that can play a vital role in the thermalization of plasma. Examples are magnetosonic solitons [6,7] and the beams of shock-reflected particles ahead of the bow shock [8], which enforce a non-stationarity of the shock [9][10][11][12]. Single-fluid MHD simulations are nevertheless used to solve problems in collisionless plasma based on the argument that they can describe the plasma dynamics on a large enough scale.…”

mentioning

confidence: 99%

Emergence of MHD structures in a collisionless PIC simulation plasma

et al. 2017

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The expansion of a dense plasma into a dilute plasma across an initially uniform perpendicular magnetic field is followed with a one-dimensional particle-in-cell (PIC) simulation over MHD time scales. The dense plasma expands in the form of a fast rarefaction wave. The accelerated dilute plasma becomes separated from the dense plasma by a tangential discontinuity at its back. A fast magnetosonic shock with the Mach number 1.5 forms at its front. Our simulation demonstrates how wave dispersion widens the shock transition layer into a train of nonlinear fast magnetosonic waves. A thermal pressure gradient in a magnetized plasma accelerates the dense plasma towards the dilute one and a rarefaction wave develops. The collision of the expanding plasma with the dilute plasma triggers shocks if the collision speed exceeds the phase velocity of the fastest ion wave. In the rest frame of the shock, the fast-moving upstream plasma is slowed down, compressed and heated as it crosses the shock and moves downstream. This net flux adds material to the downstream plasma, which lets the shock expand into the upstream direction.Shocks have been widely examined due to their key role in regulating the transfer of mass, momentum and energy in plasma. They are most easily described in a one-dimensional geometry. Shock tube experiments [1,2], which enforce such a geometry, examined shocks in partially magnetized and collisional plasma. Particle collisions equilibrate the plasma and macroscopic quantities like flow speed and temperature are uniquely defined. The time-evolution of these quantities is described well by the equations of single-fluid magnetohydrodynamics (MHD) if collisions are frequent enough to establish a thermal equilibrium between electrons and ions on the time scales of interest. Numerical shock tube experiments investigating the thermal expansion of plasma have also been performed in order to test single-fluid MHD codes, since the important MHD shocks emerge under such conditions [3,4].However, not all plasma shocks are collisional. The mean free path of the particles in the plasma, in which the Earth's bow shock [5] is immersed, is large compared to the thickness of its transition layer and it is sustained by electromagnetic fields. Collisionless plasmas support energetic structures that are not captured by a single-fluid MHD theory and that can play a vital role in the thermalization of plasma. Examples are magnetosonic solitons [6,7] and the beams of shock-reflected particles ahead of the bow shock [8], which enforce a non-stationarity of the shock [9-12]. Single-fluid MHD simulations are nevertheless used to solve problems in collisionless plasma based on the argument that they can describe the plasma dynamics on a large enough scale.Here we examine with the particle-in-cell (PIC) code EPOCH [13] the relaxation of a thermal pressure gradient in the presence of a perpendicular magnetic field. We thus perform a numerical shock tube experiment with collisionless plasma to test the hypothesis that the plasma evolut...

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The Dynamics of Very High Alfvén Mach Number Shocks in Space Plasmas

Cited by 33 publications

References 36 publications

Nonstationary Quasiperpendicular Shock and Ion Reflection at Mars

Nonstationary Quasiperpendicular Shock and Ion Reflection at Mars

Magnetic Field Amplification by the Weibel Instability at Planetary and Astrophysical Shocks with High Mach Number

Emergence of MHD structures in a collisionless PIC simulation plasma

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