Rankine‐Hugoniot Relations in Multispecies Plasma With Gyrotropic Anisotropic Downstream Ion Distributions

Gedalin, M.

doi:10.1002/2017ja024757

Cited by 6 publications

(8 citation statements)

References 42 publications

(59 reference statements)

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“…This compares very closely to the values of M a = 1.25 and s NIF = 0.26 measured for the inbound shock. The values of both parameters are also in good agreement with previous theoretical predictions (Gedalin, ).…”

Section: Resultssupporting

confidence: 91%

“…For the outbound shock with R = 1.27, the Mach number should be accordingly lower. For M A = 1.23 the theoretical prediction by Gedalin () gives s NIF = 0.38. In both cases the agreement is rather good, given the observational uncertainties and the approximations made by Gedalin ().…”

Section: Data and Observationsmentioning

confidence: 89%

“…For each set of the parameters, protons and α ‐particles are numerically traced across the shock. Their upstream distributions are taken as Maxwellian, and the downstream pressures of the species are numerically calculated and used in the pressure balance equation (Gedalin, ), where s = e , p , α . The total upstream pressure is given in equation , and the downstream electron pressure is taken as p e , xx = p e , u ( n e / n e , u ) Γ with Γ = 5/3.…”

Section: Numerical Analysis Methodologymentioning

confidence: 99%

“…This showed a general trend for the cross‐shock potential to reduce as M A increases, which is inline with theory. However, in the very low Mach number region, this trend should reverse, and the cross‐shock potential should decrease with decreasing Mach number (Gedalin, , ; Gedalin & Balikhin, ). Using equations (12) and (23) in Gedalin (), the predicted cross‐shock potential is s NIF = 0.4 for the inbound shock, with M A = 1.26 and magnetic compression R = 1.3.…”

Section: Data and Observationsmentioning

confidence: 99%

“…The results verify the theory previously proposed for the formation of such very low Mach number shocks and suggest that they are widespread when the required conditions prevail. Recent theoretical work has shown that α particles may affect the downstream magnetic profile by “spoiling” periodicity of oscillations and adding a second period (Gedalin, , ). The conditions of the THEMIS‐C observations also allow us to test these predictions.…”

Section: Introductionmentioning

confidence: 99%

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The First Direct Observational Confirmation of Kinematic Collisionless Relaxation in Very Low Mach Number Shocks Near the Earth

2019

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Collisionless shocks are ubiquitous throughout the known universe. They mainly convert the energy of the directed ion flow into heating. Upon crossing the shock front, the ion distribution becomes nongyrotropic. Relaxation to gyrotropy then occurs mainly via kinematic collisionless gyrophase mixing and interaction with waves. The theory of collisionless relaxation predicts that the downstream pressure of each ion species varies quasi-periodically with the distance from the shock transition layer and the amplitude of the variations gradually decrease. The oscillations due to each species have their own spatial period and damping scale. Pressure balance requires that the variations in the total plasma pressure should cause anticorrelating variations in the magnetic pressure. This process should occur at all Mach numbers, but its observation is difficult at moderate-/high-Mach numbers. In contrast, such magnetic oscillations have been observed at low Mach number cases of the Venusian bow shock and interplanetary shocks. In this paper, simultaneous in situ magnetic field and plasma measurements from the THEMIS-B and THEMIS-C spacecraft are used to study, for the first time, the anticorrelated total ion and magnetic pressure spatial variations at low-Mach number shocks. It is found that kinematic collisionless relaxation is the dominant process in the formation of the downstream ion distribution and in shaping the downstream magnetic profile of the observed shocks, confirming fundamental theoretical results. Comparison with the results from numerical models allows the role of the different ion species to be investigated and confirms the role heavy ions play in forming the downstream magnetic profile.

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Section: Resultssupporting

confidence: 91%

Section: Data and Observationsmentioning

confidence: 89%

Section: Numerical Analysis Methodologymentioning

confidence: 99%

Section: Data and Observationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The First Direct Observational Confirmation of Kinematic Collisionless Relaxation in Very Low Mach Number Shocks Near the Earth

2019

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Probabilities of ion scattering at the shock front

2022

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Collisionless shocks efficiently convert the energy of the directed ion flow into their thermal energy. Ion distributions change drastically at the magnetized shock crossing. Even in the absence of collisions, ion dynamics within the shock front is non-integrable and gyrophase dependent. The downstream distributions just behind the shock are not gyrotropic but become so quickly due to the kinematic gyrophase mixing even in laminar shocks. During the gyrotropization all information about gyrophases is lost. Here we develop a mapping of upstream and downstream gyrotropic distributions in terms of scattering probabilities at the shock front. An analytical expression for the probability is derived for directly transmitted ions in the narrow shock approximation. The dependence of the probability on the magnetic compression and the cross-shock potential is demonstrated.

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Oblique High Mach Number Heliospheric Shocks: The Role of α Particles

et al. 2021

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Introduction and MotivationMagnetized, collisionless shocks are ubiquitous phenomena in the heliosphere and in astrophysical plasma. Oblique or quasi-perpendicular interplanetary shocks are associated with the most energetic Coronal Mass Ejections (CMEs) and have super-Alfvénic speeds (e.g., Bale et al., 2005;Krasnoselskikh et al., 2013), with high Mach number shocks potentially most geoeffective. The Wind spacecraft, launched in 1994, provides continuous solar wind measurements on a halo orbit around the L1 Lagrange point (the distance of about 0.01 AU from the Earth toward the Sun where the spacecraft's motion around the Sun matches that of the Earth), that include magnetic field vector, and plasma properties. The Deep Space Climate Observatory (DSCOVR), launched in 2015, also around L1, in addition to Earth observing instruments, carries the Plasma-Magnetometer instruments that provides high-cadence magnetic field and plasma in-situ data. Due to their strategic location near L1, the satellites provide early warning for solar activity that propagates toward the Earth, and ample detailed heliospheric shock data. However, these single-point observations cannot provide the complete picture of the multi-dimensional multi-ion shock structure and dynamics-a gap that can be possibly filled by numerical modeling.High Mach number M (where M indicates the fast magnetosonic speed Mach number) shocks in heliospheric plasma such as the solar wind (SW) and Earths' magnetosphere were modeled with 2.5D hybrid models in the past in order to investigate ion-kinetic properties of these shocks. In the hybrid model ions are modeled as large ensemble of particles embedded in the magnetic field and electrons are fluid. Previous models focused primarily on electron-proton plasma (e.g.,

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Rankine‐Hugoniot Relations in Multispecies Plasma With Gyrotropic Anisotropic Downstream Ion Distributions

Cited by 6 publications

References 42 publications

The First Direct Observational Confirmation of Kinematic Collisionless Relaxation in Very Low Mach Number Shocks Near the Earth

The First Direct Observational Confirmation of Kinematic Collisionless Relaxation in Very Low Mach Number Shocks Near the Earth

Probabilities of ion scattering at the shock front

Oblique High Mach Number Heliospheric Shocks: The Role of α Particles

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