Resonant Whistler‐Electron Interactions: MMS Observations Versus Test‐Particle Simulation

Béhar, Etienne; Sahraoui, Fouad; Berčič, Laura

doi:10.1029/2020ja028040

Cited by 11 publications

(13 citation statements)

References 66 publications

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“…This work finds that a deficit is created in the electron VDF near v v cyclo (see Fig. 4 by Behar et al 2020). The electrons migrating from this phase-space region diffuse along the semi-circle and create an overdensity at larger pitch-angles with v v cyclo .…”

Section: The Quasi-parallel Whistler Instability Driven By the Sunward Deficitmentioning

confidence: 74%

“…The wave amplitude thus decreases, corresponding to wave damping. A resonant wave-particle interaction of this type in which energy is transferred from the waves to the electrons was studied with a test-particle approach by Behar et al (2020). This work finds that a deficit is created in the electron VDF near v v cyclo (see Fig.…”

Section: The Quasi-parallel Whistler Instability Driven By the Sunward Deficitmentioning

confidence: 99%

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Whistler instability driven by the sunward electron deficit in the solar wind

Berčič

Verscharen

Owen

et al. 2021

A&A

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Context. Solar wind electrons play an important role in the energy balance of the solar wind acceleration by carrying energy into interplanetary space in the form of electron heat flux. The heat flux is stored in the complex electron velocity distribution functions (VDFs) shaped by expansion, Coulomb collisions, and field-particle interactions. Aims. We investigate how the suprathermal electron deficit in the anti-strahl direction, which was recently discovered in the near-Sun solar wind, drives a kinetic instability and creates whistler waves with wave vectors that are quasi-parallel to the direction of the background magnetic field. Methods. We combine high-cadence measurements of electron pitch-angle distribution functions and electromagnetic waves provided by Solar Orbiter during its first orbit. Our case study is based on a burst-mode data interval from the Electrostatic Analyser System (SWA-EAS) at a distance of 112 R S (0.52 au) from the Sun, during which several whistler wave packets were detected by Solar Orbiter's Radio and Plasma Waves (RPW) instrument. Results. The sunward deficit creates kinetic conditions under which the quasi-parallel whistler wave is driven unstable. We directly test our predictions for the existence of these waves through solar wind observations. We find whistler waves that are quasi-parallel and almost circularly polarised, propagating away from the Sun, coinciding with a pronounced sunward deficit in the electron VDF. The cyclotron-resonance condition is fulfilled for electrons moving in the direction opposite to the direction of wave propagation, with energies corresponding to those associated with the sunward deficit. Conclusions. We conclude that the sunward deficit acts as a source of quasi-parallel whistler waves in the solar wind. The quasilinear diffusion of the resonant electrons tends to fill the deficit, leading to a reduction in the total electron heat flux.

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Section: The Quasi-parallel Whistler Instability Driven By the Sunward Deficitmentioning

confidence: 74%

Section: The Quasi-parallel Whistler Instability Driven By the Sunward Deficitmentioning

confidence: 99%

Whistler instability driven by the sunward electron deficit in the solar wind

Berčič

Verscharen

Owen

et al. 2021

A&A

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“…A similar behavior was observed in the study of Kajdič et al (2016) at 1 au. An energy-dependent increase in strahl PAW is expected for the resonant interaction with narrowband whistler waves (Behar et al 2020).…”

Section: Whistlers and Strahl Electronsmentioning

confidence: 99%

Whistler wave occurrence and the interaction with strahl electrons during the first encounter of Parker Solar Probe

Jagarlamudi

Wit

Froment

et al. 2021

A&A

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Aims. We studied the properties and occurrence of narrowband whistler waves and their interaction with strahl electrons observed between 0.17 and 0.26 au during the first encounter of Parker Solar Probe. Methods. We used Digital Fields Board band-pass filtered (BPF) data from FIELDS to detect the signatures of whistler waves. Additionally parameters derived from the particle distribution functions measured by the Solar Wind Electrons Alphas and Protons (SWEAP) instrument suite were used to investigate the plasma properties, and FIELDS suite measurements were used to investigate the electromagnetic (EM) fields properties corresponding to the observed whistler signatures. Results. We observe that the occurrence of whistler waves is low, nearly ~1.5% and less than 0.5% in the analyzed peak and average BPF data, respectively. Whistlers occur highly intermittently and 80% of the whistlers appear continuously for less than 3 s. The spacecraft frequencies of the analyzed waves are less than 0.2 electron cyclotron frequency (fce). The occurrence rate of whistler waves was found to be anticorrelated with the solar wind bulk velocity. The study of the duration of the whistler intervals revealed an anticorrelation between the duration and the solar wind velocity, as well as between the duration and the normalized amplitude of magnetic field variations. The pitch-angle widths (PAWs) of the field-aligned electron population referred to as the strahl are broader by at least 12 degrees during the presence of large amplitude narrowband whistler waves. This observation points toward an EM wave electron interaction, resulting in pitch-angle scattering. PAWs of strahl electrons corresponding to the short duration whistlers are higher compared to the long duration whistlers, indicating short duration whistlers scatter the strahl electrons better than the long duration ones. Parallel cuts through the strahl electron velocity distribution function (VDF) observed during the whistler intervals appear to depart from the Maxwellian shape typically found in the near-Sun strahl VDFs. The relative decrease in the parallel electron temperature and the increase in PAW for the electrons in the strahl energy range suggests that the interaction with whistler waves results in a transfer of electron momentum from the parallel to the perpendicular direction.

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“…The wider strahls observed could also result from scattering by EM fluctuations, however, due to the monotonic decreasing relation between strahl PAW and energy, some of scattering mechanisms can be ruled out. Scattering through a resonance with a whistler wave, for example, is expected to produce a peak in PAW at the resonant electron energy (Behar et al, 2020). And an electron VDF relaxation mechanism giving energy to a whistler wave would first scatter the higher energy strahl electrons, which would result in an increasing trend between PAW and energy (Verscharen et al, 2019).…”

Section: Strahl Electron Focusingmentioning

confidence: 99%

The interplay between ambipolar electric field and Coulomb collisions in the solar wind acceleration region

Berčič

Landi

Maksimović

2020

Preprint

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We use a kinetic model of expanding solar wind accounting for Coulomb collisions. This model produces a slow, supersonic solar wind proton population accelerated only through the ambipolar electric field, which arises due to the difference of mass between electron and proton.• The self-consistently calculated ambipolar electric field in the model is on the order of Dreicer electric field.• We present the radial evolution of the strahl electron component under the influence of Coulomb collisions.

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Resonant Whistler‐Electron Interactions: MMS Observations Versus Test‐Particle Simulation

Cited by 11 publications

References 66 publications

Whistler instability driven by the sunward electron deficit in the solar wind

Whistler instability driven by the sunward electron deficit in the solar wind

Whistler wave occurrence and the interaction with strahl electrons during the first encounter of Parker Solar Probe

The interplay between ambipolar electric field and Coulomb collisions in the solar wind acceleration region

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