scholarly journals Electron mirror branch: observational evidence from “historical” AMPTE-IRM and Equator-S measurements

2018 ◽  
Vol 36 (6) ◽  
pp. 1563-1576 ◽  
Author(s):  
Rudolf A. Treumann ◽  
Wolfgang Baumjohann
Keyword(s):  
Collisionless Plasma ◽  
Low Frequency ◽  
Small Population ◽  
Observational Evidence ◽  
Bulk Temperature ◽  
Temperature Anisotropy ◽  
Pressure Balance ◽  
Theoretical Evaluation ◽  
Separate Electron ◽  
Mirror Mode

Abstract. Based on now “historical” magnetic observations, supported by few available plasma data, and wave spectra from the AMPTE-IRM spacecraft, and also on “historical” Equator-S high-cadence magnetic field observations of mirror modes in the magnetosheath near the dayside magnetopause, we present observational evidence for a recent theoretical evaluation by Noreen et al. (2017) of the contribution of a global (bulk) electron temperature anisotropy to the evolution of mirror modes, giving rise to a separate electron mirror branch. We also refer to related low-frequency lion roars (whistlers) excited by the trapped resonant electron component in the high-temperature anisotropic collisionless plasma of the magnetosheath. These old data most probably indicate that signatures of the anisotropic electron effect on mirror modes had indeed already been observed long ago in magnetic and wave data, though they had not been recognised as such. Unfortunately either poor time resolution or complete lack of plasma data would have inhibited the confirmation of the required pressure balance in the electron branch for unambiguous confirmation of a separate electron mirror mode. If confirmed by future high-resolution observations (like those provided by the MMS mission), in both cases the large mirror mode amplitudes suggest that mirror modes escape quasilinear saturation, being in a state of weak kinetic plasma turbulence. As a side product, this casts as erroneous the frequent claim that the excitation of lion roars (whistlers) would eventually saturate the mirror instability by depleting the bulk temperature anisotropy. Whistlers, excited in mirror modes, just flatten the anisotropy of the small population of resonant electrons responsible for them, without having any effect on the global electron-pressure anisotropy, which causes the electron branch and by no means at all on the ion-mirror instability. For the confirmation of both the electron mirror branch and its responsibility for trapping of electrons and resonantly exciting high-frequency whistlers, also known as lion roars, high time- and energy-resolution observations of electrons (as provided for instance by MMS) are required.

scholarly journals Observational support for the electron mirror mode: AMPTE-IRM and Equator-S measurements in the magnetosheath

2018 ◽  
Author(s):  
Rudolf A. Treumann ◽  
Wolfgang Baumjohann
Keyword(s):  
High Temperature ◽  
Collisionless Plasma ◽  
Recent Theory ◽  
Dayside Magnetopause ◽  
Mirror Mode

Abstract. Based on AMPTE-IRM and Equator-S observations in the magnetosheath near the dayside magnetopause, we provide observational support for a recent theory by Noreen et al. (2017) of the contribution of the electron mirror instability to the evolution of mirror modes in the high-temperature anisotropic collisionless plasma of the magnetosheath.

scholarly journals Reduced models accounting for parallel magnetic perturbations: gyrofluid and finite Larmor radius–Landau fluid approaches

2016 ◽  
Vol 82 (6) ◽  
Author(s):  
E. Tassi ◽  
P. L. Sulem ◽  
T. Passot
Keyword(s):  
Fluid Model ◽  
Collisionless Plasma ◽  
Low Frequency ◽  
Wave Model ◽  
Plasma Phys ◽  
Alfven Wave ◽  
Larmor Radius ◽  
Closure Relation ◽  
Reduced Models ◽  
Finite Larmor Radius

Reduced models are derived for a strongly magnetized collisionless plasma at scales which are large relative to the electron thermal gyroradius and in two asymptotic regimes. One corresponds to cold ions and the other to far sub-ion scales. By including the electron pressure dynamics, these models improve the Hall reduced magnetohydrodynamics (MHD) and the kinetic Alfvén wave model of Boldyrev et al. (2013 Astrophys. J., vol. 777, 2013, p. 41), respectively. We show that the two models can be obtained either within the gyrofluid formalism of Brizard (Phys. Fluids, vol. 4, 1992, pp. 1213–1228) or as suitable weakly nonlinear limits of the finite Larmor radius (FLR)–Landau fluid model of Sulem and Passot (J. Plasma Phys., vol 81, 2015, 325810103) which extends anisotropic Hall MHD by retaining low-frequency kinetic effects. It is noticeable that, at the far sub-ion scales, the simplifications originating from the gyroaveraging operators in the gyrofluid formalism and leading to subdominant ion velocity and temperature fluctuations, correspond, at the level of the FLR–Landau fluid, to cancellation between hydrodynamic contributions and ion finite Larmor radius corrections. Energy conservation properties of the models are discussed and an explicit example of a closure relation leading to a model with a Hamiltonian structure is provided.

scholarly journals A two-fluid model describing the finite-collisionality, stationary Alfvén wave in anisotropic plasma

2008 ◽  
Vol 15 (6) ◽  
pp. 957-964 ◽  
Author(s):  
S. M. Finnegan ◽  
M. E. Koepke ◽  
D. J. Knudsen
Keyword(s):  
Fluid Model ◽  
Collisionless Plasma ◽  
Alfven Wave ◽  
Temperature Anisotropy ◽  
Thermal Pressure ◽  
Exclusion Region ◽  
Two Fluid Model ◽  
The Magnetic Field ◽  
Range Of Values ◽  
Two Fluid

Abstract. The stationary inertial Alfvén (StIA) wave (Knudsen, 1996) was predicted for cold, collisionless plasma. The model was generalized (Finnegan et al., 2008) to include nonzero values of electron and ion collisional resistivity and thermal pressure. Here, the two-fluid model is further generalized to include anisotropic thermal pressure. A bounded range of values of parallel electron drift velocity is found that excludes periodic stationary Alfvén wave solutions. This exclusion region depends on the value of the local Alfvén speed VA, plasma beta perpendicular to the magnetic field β⊥ and electron temperature anisotropy.

scholarly journals TEMPERATURE ANISOTROPY IN THE PRESENCE OF ULTRA LOW FREQUENCY WAVES IN THE TERRESTRIAL FORESHOCK

2014 ◽  
Vol 788 (1) ◽  
pp. L5 ◽  
Author(s):  
L. A. Selzer ◽  
B. Hnat ◽  
K. T. Osman ◽  
V. M. Nakariakov ◽  
J. P. Eastwood ◽  
...  
Keyword(s):  
Low Frequency ◽  
Temperature Anisotropy ◽  
Low Frequency Waves

Free energy sources in kinetic scale current sheets formed in collisionless plasma turbulence

2020 ◽  
Author(s):  
Neeraj Jain ◽  
Joerg Buechner
Keyword(s):  
Solar Wind ◽  
Free Energy ◽  
Collisionless Plasma ◽  
Plasma Turbulence ◽  
Energy Sources ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Current Sheets ◽  
Adiabatic Cooling ◽  
Collisionless Dissipation

<p>Spacecraft observations show the radial dependence of the solar wind temperature to be slower than what is expected from the adiabatic cooling of the solar wind expanding radially outwards from the sun. The most viable process considered to explain the observed slower-than-adiabatic cooling is the heating of the solar wind plasma by dissipation of the turbulent fluctuations. In solar wind which is  a collisionless plasma in turbulent state, macroscopic energy is cascaded down to kinetic scales where kinetic plasma processes can finally dissipate the energy into heat. The kinetic scale plasma processes responsible  for the dissipation of energy are, however, not well understood. A number of observational and simulation studies have shown that the heating is concentrated in and around current sheets self-consistently formed at kinetic scales. The current sheets contain free energy sources for the growth of plasma instabilities which can serve as the mechanism of the collisionless dissipation. A detailed information on the free energy sources contained in these current sheets of plasma turbulence is lacking but essential to understand the role of  plasma instabilities in collisionless dissipation.</p><p>We carry out 2-D hybrid simulations of kinetic plasma turbulence to study in detail free energy sources available in the current sheets formed in the turbulence. We focus on three free energy sources, namely, plasma density gradient, velocity gradients for both ions and electrons and ion temperature anisotropy. Our simulations show formation of current sheets in which electric current parallel to the externally applied magnetic field flows in a thickness of the order of an ion inertial length. Inside a current sheet, electron flow velocity dominates ion flow velocity in the parallel direction resulting in a larger cross-gradient of the former. The perpendicular electron velocity inside a current sheet also has variations sharper than the corresponding ion velocity. Cross gradients in plasma density are weak (under 10 % variation inside current sheets). Ion temperature is anisotropic in current sheets. Thus the current in the sheets is primarily due to electron shear flow. A theoretical model to explain the difference between electron and ion velocities in current sheets is developed. Spacecraft observations of electron shear flow in space plasma turbulence will be pointed out.   </p><p>These results suggest that the current sheets formed in kinetic plasma turbulence are close to the force free equilibrium rather than the often assumed Harris equilibrium.  This demands investigations of the linear stability properties and nonlinear evolution of force free current sheets with temperature anisotropy. Such studies can provide effective dissipation coefficients to be included in macroscopic model of the solar wind evolution.   </p>

scholarly journals Mode-coupling of low-frequency electromagnetic waves in dusty plasmas with temperature anisotropy

2007 ◽  
Vol 14 (2) ◽  
pp. 022104 ◽  
Author(s):  
M. C. de Juli ◽  
R. S. Schneider ◽  
L. F. Ziebell ◽  
R. Gaelzer
Keyword(s):  
Mode Coupling ◽  
Electromagnetic Waves ◽  
Low Frequency ◽  
Dusty Plasmas ◽  
Temperature Anisotropy

Relaxation of a temperature anisotropy in a collisionless plasma

1970 ◽  
Vol 4 (1) ◽  
pp. 21-41 ◽  
Author(s):  
C. Montes ◽  
J. Coste ◽  
G. Diener
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Relaxation Process ◽  
Time Scales ◽  
Collisionless Plasma ◽  
Electron Plasma ◽  
Temperature Anisotropy ◽  
Quasilinear Theory ◽  
Aperiodic Instability

We study the quasifinear relaxation of an aperiodic instability, namely the instability caused by the temperature anisotropy of a collisionless electron plasma in the absence of an external magnetic field. We give a detailed description of the relaxation process and we examine the validity of the quasilinear theory (existence of separate time scales, quasilinearity of the particles' orbits).

Low-frequency waves in a high-beta collisionless plasma: polarization, compressibility and helicity

1986 ◽  
Vol 35 (3) ◽  
pp. 431-447 ◽  
Author(s):  
S. Peter Gary
Keyword(s):  
Numerical Solutions ◽  
Collisionless Plasma ◽  
Low Frequency ◽  
Order Unity ◽  
Left Hand ◽  
Long Wavelength ◽  
Oblique Propagation ◽  
Ion Cyclotron ◽  
Cyclotron Mode ◽  
High Beta

This paper considers the linear theory of waves near and below the ion cyclotron frequency in an isothermal electron-ion Vlasov plasma which is isotropic, homogeneous and magnetized. Numerical solutions of the full dispersion equation for the magnetosonic/whistler and Alfvén/ion cyclotron modes at βi = 1·0 are presented, and the polarizations, compressibilities, helicities, ion Alfvén ratios and ion cross-helicities are exhibited and compared. At sufficiently large βi and θ, the angle of propagation with respect to the magnetic field, the real part of the polarization of the Alfvén/ion cyclotron wave changes sign, so that, for such parameters, this mode is no longer left-hand polarized. The Alfvén/ion cyclotron mode becomes more compressive as the wavenumber ulereases, whereas the magnetosonic/whistler becomes more compressive with increasing θ, At oblique propagation, the helicity of both modes approaches zero in the long-wavelength limit; in contrast, the ion cross-helicity is of order unity for the Alfvén/ion cyclotron wave and decreases as θ increases for the magnetosonic/whistler mode.

scholarly journals Properties of A Supercritical Quasi-Perpendicular Interplanetary Shock Propagating in Super-Alfvénic Solar Wind: from MHD to Kinetic Scales

2021 ◽  
Author(s):  
Mingzhe Liu ◽  
Zhongwei Yang ◽  
Ying D. Liu ◽  
Bertrand Lembege ◽  
Karine Issautier ◽  
...  
Keyword(s):  
Solar Wind ◽  
Energy Dissipation ◽  
Interplanetary Shock ◽  
Particle Interactions ◽  
Temperature Anisotropy ◽  
Ion Cyclotron Waves ◽  
Proton Temperature ◽  
Ion Cyclotron ◽  
Mirror Mode

<p>We investigate the properties of an interplanetary shock (M<sub>A</sub>=3.0, θ<sub>Bn</sub>=80°) propagating in Super-Alfvénic solar wind observed on September 12<sup>th,</sup> 1999 with in situ Wind/MFI and Wind/3DP observations. Key results are obtained concerning the possible energy dissipation mechanisms across the shock and how the shock modifies the ambient solar wind at MHD and kinetic scales:  (1) Waves observed in the far upstream of the shock are incompressional and mostly shear Alfvén waves.  (2) In the downstream, the shocked solar wind shows both Alfvénic and mirror-mode features due to the coupling between the Alfvén waves and ion mirror-mode waves.  (3) Specularly reflected gyrating ions, whistler waves, and ion cyclotron waves are observed around the shock ramp, indicating that the shock may rely on both particle reflection and wave-particle interactions for energy dissipation.  (4) Both ion cyclotron and mirror mode instabilities may be excited in the downstream of the shock since the proton temperature anisotropy touches their thresholds due to the enhanced proton temperature anisotropy.  (5) Whistler heat flux instabilities excited around the shock give free energy for the whistler precursors, which help explain the isotropic electron number and energy flux together with the normal betatron acceleration of electrons across the shock.  (6) The shock may be somehow connected to the electron foreshock region of the Earth’s bow shock, since Bx > 0, By < 0, and the electron flux varies only when the electron pitch angles are less than PA = 90°, which should be further investigated. Furthermore, the interaction between Alfvén waves and the shock and how the shock modifies the properties of the Alfvén waves are also discussed.</p>

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