Solar Wind Plasma Particles Organized by the Flow Speed

Pierrard, Viviane; Lazar, M.; Štverák, S.

doi:10.1007/s11207-020-01730-z

Cited by 13 publications

(15 citation statements)

References 45 publications

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“…Thus, low densities of the core corresponds to low values of κ: this indicates that high suprathermal tails for the halo are more present in low-density plasmas, when interactions between the particles, i.e., Coulomb collisions, are less frequent. The same conclusion is valid for the total number density, since it is close to the core density, as the ratio between halo and core density is always lower than 20% (Pierrard et al, 2020). This is quite logical since higher densities lead to VDF closer to Maxwellians, due to higher effects of Coulomb collisions, as shown in solar wind simulations based on the Fokker-Planck equation including Coulomb collisions (Pierrard et al, 2001b).…”

Section: Halo Temperature (T H ) Versus Kappa Exponent (κ)supporting

confidence: 58%

“…at 0.4 AU (Pierrard et al, 2016). Pierrard et al (2020) had already shown that low halo density was associated to a higher bulk velocity. In the following, we study the interlinks between n h and other electron characteristics, first considering the core density n c .…”

Section: Influence Of the Halo Densitymentioning

confidence: 88%

“…At low distance (Helios observations), the spread of data is very large for high values of κ, while the low values of κ are more rare and associated to values around 500 km/s. At higher distances, the variation of velocity as a function of κ is not anymore significant (Pierrard et al, 2020). The link between the bulk velocity and the suprathermal population was already briefly studied in Lazar et al (2020a).…”

Section: Bulk Velocity (U) Versus Kappa Exponent (κ)mentioning

confidence: 96%

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Implications of Kappa Suprathermal Halo of the Solar Wind Electrons

Pierrard

Lazar

Štverák

2022

Front. Astron. Space Sci.

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The electron velocity distributions measured in-situ in space plasmas reveal two central populations, a low-energy and highly dense (quasi-)thermal core, and a more diffuse but hotter suprathermal halo. Even if the core contributes much more to the total number density than the suprathermal particles, the energetic electrons play an important role in the higher moments. Using a dataset of more than 120,000 solar wind observations of electron distributions, measured in the ecliptic between 0.35 and 3.3 AU, we investigate here the main characteristics of the halo population and its potential influence on the core, and macroscopic properties of electrons, i.e., number density (n), bulk velocity (u), temperature (T) and temperature anisotropy (T⊥/Τ//). The analysis indicates that the parameters exhibit interdependence trends characterized by correlations between certain of these parameters and the kappa exponent (κ) corresponding to the power law of the halo population tail. The links between low kappa and low number densities (of both the core and halo populations) confirm that Coulomb collisions can be quite ineffective even at low radial distances if the density of the plasma is sufficiently low. Moreover, halo populations with lower values of κ are also associated to higher temperature anisotropies, and to higher bulk velocity. An interdependence between core and halo populations is also suggested by an apparent (inverse) correlation between their density and temperature ratios. We further show relations between the parameters fitting the sum of a Maxwellian core and a Kappa halo, and those of a global (single) Kappa fit that incorporates both the core and halo components. Such a global Kappa is used in an exospheric model of the solar wind, to predict the influence of suprathermal electrons on the characteristics of the solar wind. These results should stimulate future detailed analysis of these relationships and correlations, which may contribute to a realistic modeling of the solar wind and the formation and evolution of suprathermal populations.

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Section: Halo Temperature (T H ) Versus Kappa Exponent (κ)supporting

confidence: 58%

Section: Influence Of the Halo Densitymentioning

confidence: 88%

Section: Bulk Velocity (U) Versus Kappa Exponent (κ)mentioning

confidence: 96%

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Implications of Kappa Suprathermal Halo of the Solar Wind Electrons

Pierrard

Lazar

Štverák

2022

Front. Astron. Space Sci.

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“…It is primarily observed at energies above a breakpoint of about 50 eV at 1 au (green colour in Figure 1; McComas et al, 1992;Lie-Svendsen et al, 1997). The location of this breakpoint and the relative density of the halo population vary with distance from the Sun and show correlations with solar-wind parameters such as speed and temperature (Maksimovic et al, 2000(Maksimovic et al, , 2005Pierrard et al, 2016Pierrard et al, , 2020Bakrania et al, 2020). The halo population is often successfully modelled with a κ-distribution (using the Greek letter "kappa"; for detailed information about κ-distributions, see the recent textbooks by Livadiotis, 2017 and.…”

Section: Introductionmentioning

confidence: 97%

Electron-Driven Instabilities in the Solar Wind

Verscharen

Chandran²,

Boella³

et al. 2022

Front. Astron. Space Sci.

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The electrons are an essential particle species in the solar wind. They often exhibit non-equilibrium features in their velocity distribution function. These include temperature anisotropies, tails (kurtosis), and reflectional asymmetries (skewness), which contribute a significant heat flux to the solar wind. If these non-equilibrium features are sufficiently strong, they drive kinetic micro-instabilities. We develop a semi-graphical framework based on the equations of quasi-linear theory to describe electron-driven instabilities in the solar wind. We apply our framework to resonant instabilities driven by temperature anisotropies. These include the electron whistler anisotropy instability and the propagating electron firehose instability. We then describe resonant instabilities driven by reflectional asymmetries in the electron distribution function. These include the electron/ion-acoustic, kinetic Alfvén heat-flux, Langmuir, electron-beam, electron/ion-cyclotron, electron/electron-acoustic, whistler heat-flux, oblique fast-magnetosonic/whistler, lower-hybrid fan, and electron-deficit whistler instability. We briefly comment on non-resonant instabilities driven by electron temperature anisotropies such as the mirror-mode and the non-propagating firehose instability. We conclude our review with a list of open research topics in the field of electron-driven instabilities in the solar wind.

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“…1; McComas et al, 1992;Lie-Svendsen et al, 1997). The location of this breakpoint and the relative density of the halo population vary with distance from the Sun and show correlations with solar-wind parameters such as speed and temperature (Maksimovic et al, 2000(Maksimovic et al, , 2005Pierrard et al, 2016Pierrard et al, , 2020Bakrania et al, 2020). The halo population is often successfully modelled with a κ-distribution (using the Greek letter "kappa"; for detailed information about κ-distributions, see the recent textbooks by Livadiotis, 2017 andFichtner, 2021).…”

Section: Introductionmentioning

confidence: 99%

Electron-driven instabilities in the solar wind

Verscharen¹,

Chandran²,

Boella³

et al. 2022

Preprint

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The electrons are an essential particle species in the solar wind. They often exhibit nonequilibrium features in their velocity distribution function. These include temperature anisotropies, tails (kurtosis), and reflectional asymmetries (skewness), which contribute a significant heat flux to the solar wind. If these non-equilibrium features are sufficiently strong, they drive kinetic micro-instabilities. We develop a semi-graphical framework based on the equations of quasi-linear theory to describe electron-driven instabilities in the solar wind. We apply our framework to resonant instabilities driven by temperature anisotropies. These include the electron whistler anisotropy instability and the propagating electron firehose instability. We then describe resonant instabilities driven by reflectional asymmetries in the electron distribution function. These include the electron/ion-acoustic, kinetic Alfv én heat-flux, Langmuir, electron-beam, electron/ion-cyclotron, 1

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Solar Wind Plasma Particles Organized by the Flow Speed

Cited by 13 publications

References 45 publications

Implications of Kappa Suprathermal Halo of the Solar Wind Electrons

Implications of Kappa Suprathermal Halo of the Solar Wind Electrons

Electron-Driven Instabilities in the Solar Wind

Electron-driven instabilities in the solar wind

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