Observations of diffusion in the electron halo and strahl

Gurgiolo, C.; Goldstein, M. L.

doi:10.5194/angeo-34-1175-2016

Cited by 10 publications

(8 citation statements)

References 37 publications

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“…Our predicted evolution of the electron VDF is consistent with the observed formation of a proto-halo through strahl scattering (Gurgiolo et al 2012). However, further observations are ambiguous regarding the exact source of the proto-halo (Gurgiolo & Goldstein 2016). Future high-resolution electron observations with Solar Orbiter and Parker Solar Probe at different distances from the Sun may help us resolve these ambiguities.…”

Section: Discussionsupporting

confidence: 80%

“…Even though this instability does not cause significant strahl scattering, we argue that it contributes to the initial formation of the halo population. However, other mechanisms must be considered to account for the full strahl scattering, in agreement with observations (Gurgiolo et al 2012;Gurgiolo & Goldstein 2016).…”

Section: Discussion Of the Strahl Scatteringsupporting

confidence: 74%

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A Quasi-linear Diffusion Model for Resonant Wave–Particle Instability in Homogeneous Plasma

Jeong

Verscharen

Wicks

et al. 2020

ApJ

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In this paper, we develop a model to describe the generalized wave-particle instability in a quasi-neutral plasma. We analyze the quasi-linear diffusion equation for particles by expressing an arbitrary unstable and resonant wave mode as a Gaussian wave packet, allowing for an arbitrary direction of propagation with respect to the background magnetic field. We show that the localized energy density of the Gaussian wave packet determines the velocityspace range in which the dominant wave-particle instability and counteracting damping contributions are effective. Moreover, we derive a relation describing the diffusive trajectories of resonant particles in velocity space under the action of such an interplay between the wave-particle instability and damping. For the numerical computation of our theoretical model, we develop a mathematical approach based on the Crank-Nicolson scheme to solve the full quasi-linear diffusion equation. Our numerical analysis solves the time evolution of the velocity distribution function under the action of a dominant wave-particle instability and counteracting damping and shows a good agreement with our theoretical description. As an application, we use our model to study the oblique fastmagnetosonic/whistler instability, which is proposed as a scattering mechanism for strahl electrons in the solar wind. In addition, we numerically solve the full Fokker-Planck equation to compute the time evolution of the electron-strahl distribution function under the action of Coulomb collisions with core electrons and protons after the collisionless action of the oblique fast-magnetosonic/whistler instability.

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Section: Discussionsupporting

confidence: 80%

Section: Discussion Of the Strahl Scatteringsupporting

confidence: 74%

A Quasi-linear Diffusion Model for Resonant Wave–Particle Instability in Homogeneous Plasma

Jeong

Verscharen

Wicks

et al. 2020

ApJ

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“…1.91 ) × 10 −6 # s −1 ; and νecc ∼ (6.45 11.0 3.31 ) × 10 −6 # s −1 . The majority of the literature on the strahl electrons focus entirely on the pitch-angle width versus energy and/or radial distance from the sun (e.g., Anderson et al 2012;Kajdič et al 2016;Gurgiolo et al 2012;Gurgiolo & Goldstein 2016;Horaites et al 2018;Pagel et al 2007;Walsh et al 2013) or they compute the total heat flux of the distribution (e.g., Crooker et al 2003;Crooker & Pagel 2008;Pagel et al 2005b,a). A few studies examined density ratios among the various components (e.g., Maksimovic et al 2005;Štverák et al 2009) and some have extrapolated an effective temperature (e.g., Tao et al 2016a,b) from a limited energy range measurement.…”

Section: Summary Of Upstream Statisticsmentioning

confidence: 99%

Supplement to: Electron energy partition across interplanetary shocks

Wilson¹,

Chen²,

Wang³

et al. 2019

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Analysis of model fit results of 15,210 electron velocity distribution functions (VDFs), observed within ±2 hours of 52 interplanetary (IP) shocks by the Wind spacecraft near 1 AU, is presented as the third and final part on electron VDFs near IP shocks. The core electrons and protons dominate in the magnitude and change in the partial-to-total thermal pressure ratio, with the core electrons often gaining as much or more than the protons. Only a moderate positive correlation is observed between the electron temperature and the kinetic energy change across the shock, while weaker, if any, correlations were found with any other macroscopic shock parameter. No VDF parameter correlated with the shock normal angle. The electron VDF evolves from a narrowly peaked core with flaring suprathermal tails in the upstream to either a slightly hotter core with steeper tails or much hotter flattop core with even steeper tails downstream of the weaker and strongest shocks, respectively. Both quasi-static and fluctuating fields are examined as possible mechanisms modifying the VDF but neither is sufficient alone. For instance, flattop VDFs can be generated by nonlinear ion acoustic wave stochastic acceleration (i.e., inelastic collisions) while other work suggested they result from the combination of quasi-static and fluctuating fields. This three-part study shows that not only are these systems not thermodynamic in nature, even kinetic models may require modification to include things like inelastic collision operators to properly model electron VDF evolution across shocks or in the solar wind.

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“…Return distributions are almost always field aligned and are often nongyrotropic for both electrons and ions. The anisotropy is basically the result of gyrophase bunching that can occur in the reflection process (Gurgiolo et al, 1983) and is integral to the formation of the partial and full ring distributions observed in the foreshock. Those distributions are thought to be derived from the phase mixing of initially gyrophase-bunched distributions as they propagate away from the shock (Gurgiolo et al, 1993;Mesiane et al, 2001;Meziane et al, 2004).…”

Section: The Solar Wind Ion Velocity Distribution Function (Vdf)mentioning

confidence: 99%

“…For a full description, see Gurgiolo et al (2010). A detailed description of how the moments are computed as well as how to separate electron populations within an eVDF can be found in Gurgiolo and Goldstein (2016). In the analysis presented here we use a slightly modified version of the population isolation method described in the aforementioned paper.…”

Section: φ-θ Plots and Momentsmentioning

confidence: 99%

Reflection of the strahl within the foot of the Earth's bow shock

Gurgiolo¹,

Goldstein

Viñas

2019

Ann. Geophys.

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Abstract. The reflection of a fraction of the solar wind at the bow shock to some extent defines the physical properties of what is known as the foreshock, the region where the interplanetary magnetic field has a direct connection to the bow shock. Both ion and electron reflection have been observed and together form a significant source of free energy that is responsible for many of the instabilities observed in this region. In this paper we concentrate on the reflection of electrons at the shock and report two significant findings: the first is that the strahl, the field-aligned component of the electron solar wind distribution, appears to be fully reflected at the bow shock; the second finding is that the reflection is observed to occur in the foot of the shock and not in the shock ramp. This latter observation implies that mirroring in these examples is not the primary determinant of the electron reflection process.

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Observations of diffusion in the electron halo and strahl

Cited by 10 publications

References 37 publications

A Quasi-linear Diffusion Model for Resonant Wave–Particle Instability in Homogeneous Plasma

A Quasi-linear Diffusion Model for Resonant Wave–Particle Instability in Homogeneous Plasma

Supplement to: Electron energy partition across interplanetary shocks

Reflection of the strahl within the foot of the Earth's bow shock

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