Evolution of the solar wind proton temperature anisotropy from 0.3 to 2.5 AU

Matteini, Lorenzo; Landi, Simone; Hellinger, Petr; Pantellini, Filippo; Maksimović, M.; Velli, Marco; Goldstein, B. E.; Marsch, E.

doi:10.1029/2007gl030920

Cited by 215 publications

(239 citation statements)

References 18 publications

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“…Thus, an implication of the large scale mechanisms in generating temperature anisotropy of plasma particles seems to be confirmed by the observations, which show a radial evolution of the temperature anisotropy from an exclusive A = T ⊥ /T > 1 at low heliocentric distances ∼ 0.3 AU (Matteini et al 2007), where the interplanetary magnetic field is more intense, to a dominant A < 1 after the expansion at large radial distances ∼ 1 AU (Kasper et al 2003;Štverák et al 2008). On the other hand, the anisotropy-driven instabilities enhance the small-scale fluctuations, which may play two distinct roles, either to maintain the anisotropy correlation of the electrons and protons, e.g., by cyclotron electromagnetic instabilities, or to transfer the free energy between plasma species, e.g., by firehose instability, and eventually induce an anti-correlation of their anisotropies.…”

Section: Introductionsupporting

confidence: 66%

Shaping the solar wind temperature anisotropy by the interplay of electron and proton instabilities

Shaaban

Lazar

Poedts³

et al. 2016

Astrophys Space Sci

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A variety of nonthermal characteristics like kinetic, e.g., temperature, anisotropies and suprathermal populations (enhancing the high energy tails of the velocity distributions) are revealed by the in-situ observations in the solar wind indicating quasistationary states of plasma particles out of thermal equilibrium. Large deviations from isotropy generate kinetic instabilities and growing fluctuating fields which should be more efficient than collisions in limiting the anisotropy (below the instability threshold) and explain the anisotropy limits reported by the observations. The present paper aims to decode the principal instabilities driven by the temperature anisotropy of electrons and protons in the solar wind, and contrast the instability thresholds with the bounds observed at 1 AU for the temperature anisotropy. The instabilities are characterized using linear kinetic theory to identify the appropriate (fastest) instability in the relaxation of temperature anisotropies A e,p = T e,p,⊥ /T e,p, = 1. The analysis focuses on the electromagnetic instabilities driven by the anisotropic protons (A p ≶ 1) and invokes for the first time a dynamical model to capture the interplay with the anisotropic electrons by correlating the effects of these two species of plasma particles, dominant in the solar wind.

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Section: Introductionsupporting

confidence: 66%

Shaping the solar wind temperature anisotropy by the interplay of electron and proton instabilities

Shaaban

Lazar

Poedts³

et al. 2016

Astrophys Space Sci

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“…For this demonstration, we neglect fluctuations in B and n p and treat B 0 and n 0 as the values of B and n at the distance r at which = R R p 0 p and   b b = p 0 p . The radial decrease in B and n p in the solar wind suggests that R p decreases with radial distance r from the Sun, while  b p increases with r under the first-order assumption of a radial split-monopole magnetic field and a radial flow with r-independent bulk speed, i.e., B ∝ r −2 and µ -n r p 2 (Matteini et al 2007(Matteini et al , 2012Hellinger & Trávníček 2015;. The split-monopole approximation breaks down at larger r due to the increasing average angle between the magnetic-field direction and the radial direction.…”

Section: Appendix C Estimate For the Minimum Fm/w Amplitude For Effecmentioning

confidence: 99%

Collisionless Isotropization of the Solar-Wind Protons by Compressive Fluctuations and Plasma Instabilities

Verscharen

Chandran

Klein

et al. 2016

ApJ

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p , whereT p and  T p are the perpendicular and parallel temperatures of the protons, B is the magnetic field strength, and n p is the proton density. If the amplitude of the compressive fluctuations is large enough, R p crosses one or more instability thresholds for anisotropy-driven microinstabilities. The enhanced field fluctuations from these microinstabilities scatter the protons so as to reduce the anisotropy of the pressure tensor. We propose that this scattering drives the average value of R p away from the marginal stability boundary until the fluctuating value of R p stops crossing the boundary. We model this "fluctuating-anisotropy effect" using linear VlasovMaxwell theory to describe the large-scale compressive fluctuations. We argue that this effect can explain why, in the nearly collisionless solar wind, the average value of R p is close to unity.

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“…Therefore, only k ⊥ wave vectors are well resolved. Šafránková et al (2013) 2013) or ion anisotropy instabilities Matteini et al 2007) may be responsible for the spectral variability within the transition range.…”

Section: Turbulence Around Ion Scalesmentioning

confidence: 99%

“…At these small scales ion temperature anisotropy instabilities can occur Marsch 2006;Matteini et al 2007), and may remove energy from, or also inject it into, the turbulence.…”

Section: Ion Scale Instabilities Driven By Solar Wind Expansion and Cmentioning

confidence: 99%

“…Several early authors studied this possibility and looked for evidence of instability (Gary et al 1976(Gary et al , 1996Kasper 2002;Hellinger et al 2006;Matteini et al 2007;Bourouaine et al 2010). Relatively recent results of using well-calibrated, statistical measurements from the Wind spacecraft have shown that the proton temperature anisotropy T ⊥ /T || is constrained by the β || 15 -dependent thresholds for the oblique firehose instability (for T ⊥ /T || < 1) and the mirror-mode instability (for T ⊥ /T || > 1) suggesting that the growth of ion-scale fluctuations acts to isotropize the plasma near the thresholds (Gary 1993).…”

Section: Ion Scale Instabilities Driven By Solar Wind Expansion and Cmentioning

confidence: 99%

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Solar Wind Turbulence and the Role of Ion Instabilities

et al. 2013

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Solar wind is probably the best laboratory to study turbulence in astrophysical plasmas. In addition to the presence of magnetic field, the differences with neutral fluid isotropic turbulence are: (i) weakness of collisional dissipation and (ii) presence of several characteristic space and time scales. In this paper we discuss observational properties of solar wind turbulence in a large range from the MHD to the electron scales. At MHD scales, within the inertial range, turbulence cascade of magnetic fluctuations develops mostly in the plane perpendicular to the mean field, with the Kolmogorov scaling k −5/3 ⊥ for the perpendicular cascade and k −2 for the parallel one. Solar wind turbulence is compressible in nature: density fluctuations at MHD scales have the Kolmogorov spectrum. Velocity fluctuations do not follow magnetic field ones: their spectrum is a power-law with a −3/2 spectral index. Probability distribution functions of different plasma parameters are not Gaussian, indicating presence of intermittency. At the moment there is no global model taking into account all these observed properties of the inertial range. At ion scales, turbulent spectra have a break, compressibility increases and the density fluctuation spectrum has a local flattening. Around ion scales, magnetic spectra are variable and ion instabilities occur as a function of the local plasma parameters. Between ion and electron scales, a small scale turbulent cascade seems to be established. It is characterized by a well defined power-law spectrum in magnetic and density fluctuations with a spectral index close to −2.8. Approaching electron scales, the fluctuations are no more self-similar: an exponential cut-off is usually observed (for time intervals without quasi-parallel whistlers) indicating an onset of dissipation. The small scale inertial range between ion and electron scales and the electron dissipation range can be together described by ∼ k −α ⊥ exp(−k ⊥ d ), with α 8/3 and the dissipation scale d close to the electron Larmor radius d ρ e . The nature of this small scale cascade and a possible dissipation mechanism are still under debate.

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Evolution of the solar wind proton temperature anisotropy from 0.3 to 2.5 AU

Cited by 215 publications

References 18 publications

Shaping the solar wind temperature anisotropy by the interplay of electron and proton instabilities

Shaping the solar wind temperature anisotropy by the interplay of electron and proton instabilities

Collisionless Isotropization of the Solar-Wind Protons by Compressive Fluctuations and Plasma Instabilities

Solar Wind Turbulence and the Role of Ion Instabilities

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