Nongyrotropic particle distributions in space plasmas

Motschmann, U.; Glaßmeier, K.‐H.; Brinca, A. L.

doi:10.1007/s00585-999-0613-4

Cited by 12 publications

(11 citation statements)

References 26 publications

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“…It is important to point out that in certain parameter regimes other that what is considered here, the introduction of a nongyrotropic plasma distribution by itself can generate an instability when the corresponding gyrotropic situation is stable. This is true for both stationary [ Brinca and Romeiras , 1998; Brinca et al , 1998; Brinca , 1999; Motschmann and Glassmeier , 1998; Motschmann et al , 1999] and time‐varying [ Motschmann et al , 1999] nongyrotropic distributions.…”

Section: Results Of Hybrid Simulationsmentioning

confidence: 94%

“…Similar conclusions were made on the basis of linear stability studies by Brinca and Romeiras [1998]and Brinca [1999], who showed that in certain parameter regimes, parallel propagating waves are stable in the presence of time‐varying nongyrotropic distributions, unless a finite perpendicular current exists. Motschmann et al [1999] found that a time‐varying nongyrotropic plasma is linearly stable to parallel propagating waves, for certain parameters, unless an additional energy contribution such as a temperature anisotropy is present. Motschmann et al [1999] also states that nongyrotropic distributions are expected to be stable when both the perpendicular and parallel velocities are conserved and particle diffusion occurs along the gyrophase angle only.…”

Section: Discussionmentioning

confidence: 99%

“… Motschmann et al [1999] found that a time‐varying nongyrotropic plasma is linearly stable to parallel propagating waves, for certain parameters, unless an additional energy contribution such as a temperature anisotropy is present. Motschmann et al [1999] also states that nongyrotropic distributions are expected to be stable when both the perpendicular and parallel velocities are conserved and particle diffusion occurs along the gyrophase angle only. This is because particle energy is independent of phase angle.…”

Section: Discussionmentioning

confidence: 99%

“… Brinca [1999]studied the linear stability of both stationary and time‐varying nongyrotropic distributions and showed that their free energy can destabilize a plasma and enhance the growth of instabilities driven by gyrotropic distributions. The linear theory of both stationary and time‐varying nongyrotropic distributions was also studied by Motschmann and Glassmeier [1998] and Motschmann et al [1999] for a particular parameter regime. They showed that stationary nongyrotropic distributions drive both perpendicular and parallel propagating waves unstable, while time stationary nongyrotropic distributions led primarily to an instability of perpendicular waves.…”

Section: Introductionmentioning

confidence: 99%

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Wave‐particle interactions associated with nongyrotropic distribution functions: A hybrid simulation study

Convery

Schriver²,

Ashour‐Abdalla

et al. 2002

J. Geophys. Res.

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[1] Nongyrotropic plasma distribution functions can be formed in regions of space where guiding center motion breaks down as a result of strongly curved and weak ambient magnetic fields. Such are the conditions near the current sheet in the Earth's middle and distant magnetotail, where observations of nongyrotropic ion distributions have been made [Frank et al., 1994]. Here a systematic parameter study of nongyrotropic proton distributions using electromagnetic hybrid simulations is made. We model the observed nongyrotropic distributions by removing a number of arc length segments from a cold ring distribution and find significant differences with the results of simulations that initially have a gyrotropic ring distribution. Model nongyrotropic distributions with initially small perpendicular thermalization produce growing fluctuations that diffuse the ions into a stable Maxwellian-like distribution within a few proton gyro periods. The growing waves produced by nongyrotropic distributions are similar to the electromagnetic proton cyclotron waves produced by a gyrotropic proton ring distribution in that they propagate parallel to the background magnetic field and occur at frequencies on the order of the proton gyrofrequency. The maximum energy of the fluctuating magnetic field increases as the initial proton distribution is made more nongyrotropic, that is, more highly bunched in perpendicular velocity space. This increase can be as much as twice the energy produced in the gyrotropic case.

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Section: Results Of Hybrid Simulationsmentioning

confidence: 94%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Wave‐particle interactions associated with nongyrotropic distribution functions: A hybrid simulation study

Convery

Schriver²,

Ashour‐Abdalla

et al. 2002

J. Geophys. Res.

View full text Add to dashboard Cite

show abstract

“…We noted at the beginning of section 4 that the reflected protons are not gyrotropic as we assume in the quasilinear analysis, since their motion is coherent in gyrophase. However, Motschmann et al [1999] investigated the stability of a nongyrotropic ion distribution and concluded that the gradients in gyrophase do not introduce new strong instabilities to compete with that which we consider here.…”

Section: Discussionmentioning

confidence: 94%

A quasilinear theory of ion “thermalization” and wave excitation downstream of Earth's bow shock

2005

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[1] A quasilinear theory is presented for the relaxation of the proton and helium distribution functions and the associated excitation of ion cyclotron waves, downstream of the quasi-perpendicular Earth's bow shock. The theory predicts the wave polarization, power and peak frequency, and the proton bulk velocity and temperature anisotropy, sufficiently far downstream of the shock that the ions and waves have relaxed to a quasiequilibrium. The results are compared with the AMPTE/IRM crossings of the marginally supercritical bow shock documented by Sckopke et al. (1990), for which the number of ''reflected'' protons is small and the quasilinear approximation is expected to be valid. The theory starts with the trajectories of the specularly reflected protons and transmitted helium in the laminar electromagnetic fields of the shock transition. In a simplified treatment of the downstream relaxation process, neglecting wave dispersion and assuming that the downstream reflected proton speed v 0 is large compared with the Alfven speed V A , the wave and proton quasi-equilibrium predictions are qualitatively in agreement with the observations. In a more precise treatment limited to a perpendicular configuration, in which dispersion is included and v 0 may be comparable with V A , the agreement with the observations is generally very good if the contribution of the transmitted core protons is included. One interesting feature is that the minor ion helium may contribute to the wave power, and in return change the proton and helium distribution functions. The helium contribution is estimated but requires further investigation.

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On the origin of the quasi‐perpendicular ion foreshock: Full‐particle simulations

2013

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[1] Many space missions have already evidenced the existence of the ion foreshock region located upstream of the Earth's bow shock and populated by energetic backstreaming ions reflected by the shock front. In order to analyze this region, a curved shock is simulated with a 2-D particle-in-cell (PIC) code. The analysis is presently restricted to the quasi-perpendicular angular range defined by 45 ı Ä Â Bn Ä 90 ı . In agreement with experimental data, present results evidence two distinct ion populations backstreaming from the shock front along the interplanetary magnetic field: (i) the field-aligned beam population (hereafter "FAB") and (ii) the gyrophase bunched population (hereafter "GPB") which differ from each other by their gyrotropic or non-gyrotropic behavior, respectively. Excluded by a simulation time which is too short, ion instabilities pitch-angle scattering cannot be the source of "GPB." Two new criteria are proposed to identify more precisely each population: their interaction time t int with the shock front and their downstream penetration depth. These criteria show that (i) the "FAB" population moves back and forth between the upstream edge of the shock front and the overshoot, and is characterized by a t int covering several upstream gyroperiods.(ii) In contrast, the "GPB" ions suffer a short interaction time (i.e., 1 < ci ). We observe that the "FAB" ions may have different origins although all "GPB" ions seem to be produced by the electrostatic field built up at the shock and are emitted in a burst-like mode rather than in continuous way.

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Nongyrotropic particle distributions in space plasmas

Cited by 12 publications

References 26 publications

Wave‐particle interactions associated with nongyrotropic distribution functions: A hybrid simulation study

Wave‐particle interactions associated with nongyrotropic distribution functions: A hybrid simulation study

A quasilinear theory of ion “thermalization” and wave excitation downstream of Earth's bow shock

On the origin of the quasi‐perpendicular ion foreshock: Full‐particle simulations

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