On the evolution of outward and inward Alfvénic fluctuations in the polar wind

Bavassano, B.; Pietropaolo, E.; Bruno, R.

doi:10.1029/1999ja000276

Cited by 121 publications

(157 citation statements)

References 17 publications

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“…Thus, the broadening of the y and z components of the ion velocity distribution functions is due to the presence of AWs (usual wave broadening, which is actually observed e.g. in the solar corona and solar wind, Belcher & Davis 1971;Smith et al 1995;Bavassano et al 2000), and hence there is no ion acceleration present. Note that y and z components and hence total kinetic energy of ions is monotonously increasing due to continuous AW driving.…”

Section: Resultsmentioning

confidence: 99%

Particle-In-Cell simulations of circularly polarised Alfvén wave phase mixing: A new mechanism for electron acceleration in collisionless plasmas

Tsiklauri

Sakai

Saito

2005

A&A

113

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Abstract. In this work we used Particle-In-Cell simulations to study the interaction of circularly polarised Alfvén waves with one dimensional plasma density inhomogeneities transverse to the uniform magnetic field (phase mixing) in collisionless plasmas. In our preliminary work we reported discovery of a new electron acceleration mechanism, in which progressive distortion of the Alfvén wave front, due to the differences in local Alfvén speed, generates an oblique (nearly parallel to the magnetic field) electrostatic field. The latter accelerates electrons through the Landau resonance. Here we report a detailed study of this novel mechanism, including: (i) analysis of broadening of the ion distribution function due to the presence of Alfvén waves; and (ii) the generation of compressive perturbations due to both weak non-linearity and plasma density inhomogeneity. The amplitude decay law in the inhomogeneous regions, in the kinetic regime, is demonstrated to be the same as in the MHD approximation described by Heyvaerts & Priest (1983, A&A, 117, 220).

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Section: Resultsmentioning

confidence: 99%

Particle-In-Cell simulations of circularly polarised Alfvén wave phase mixing: A new mechanism for electron acceleration in collisionless plasmas

Tsiklauri

Sakai

Saito

2005

A&A

113

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“…A fast, teneous, and steady flow, as compared to low-latitude conditions, the polar wind is the best example in the heliosphere of an almost structureless flow. As typical of the fast wind regime (Tu and Marsch, 1995), the polar wind is characterized by the presence of a strong flow of fluctuations of Alfvénic type (e.g., Goldstein et al, 1995b;Smith et al, 1995;Bavassano et al, 2000). to 80 • of latitude, with extended full immersions in the polar wind.…”

Section: Introductionmentioning

confidence: 99%

On the distribution of energy versus Alfvénic correlation for polar wind fluctuations

Bavassano

Bruno

2006

Ann. Geophys.

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Abstract. Previous analyses have shown that polar wind fluctuations at MHD scales appear as a mixture of Alfvénic fluctuations and variations with an energy imbalance in favour of the magnetic term. In the present study, by separately examining the behaviour of kinetic and magnetic energies versus the Alfvénic correlation level, we unambiguously confirm that the second population is essentially related to a large increase of the magnetic energy with respect to that of the Alfvénic population. The relevant new result is that this magnetic population, though of secondary importance in terms of occurrence frequency, corresponds to a primary peak in the distribution of total energy. The fact that this holds in the case of polar wind, which is the least structured type of interplanetary plasma flow and with the slowest evolving Alfvénic turbulence, strongly suggests the general conclusion that magnetic structures cannot be neglected when modeling fluctuations for all kinds of wind regime.

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“…as in the near-Sun solar wind and coronal holes (Bavassano et al 2000;Cranmer & van Ballegooijen 2005). We then drop terms that are δz…”

Section: Reflection-driven Grmhd Turbulencementioning

confidence: 99%

Heating of accretion-disk coronae and jets by general relativistic magnetohydrodynamic turbulence

2018

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Turbulence in an accretion disk launches Alfvén waves (AWs) that propagate away from the disk along magnetic-field lines. Because the Alfvén speed varies with distance from the disk, the AWs undergo partial non-WKB reflection, and counter-propagating AWs subsequently interact, causing AW energy to cascade to small scales and dissipate. To investigate this process, we introduce an Elsasser-like formulation of general relativistic magnetohydrodynamics (GRMHD) and develop the theory of general relativistic reduced MHD in an inhomogeneous medium. We then derive a set of equations for the mean-square AW amplitude M + and turbulent heating rate Q under the assumption that, in the plasma rest frame, AWs propagating away from the disk are much more energetic than AWs propagating toward the disk. For the case in which the background flow is axisymmetric and time independent, we solve these equations analytically to determine M + and Q as functions of position. We find that, for an idealized thin disk threaded by a large-scale poloidal magnetic field, the AW energy flux isnet,d times the disk's radiative flux, where ρ b and ρ d are the mass densities at the coronal base and disk midplane, respectively, and β net,d is the ratio (evaluated at the disk midplane) of plasma-plus-radiation pressure to the pressure of the average vertical magnetic field. This energy flux could have a significant impact on disk coronae and outflows. To lay the groundwork for future global simulations of turbulent disk coronae and jets, we derive a set of averaged GRMHD equations that account for reflection-driven AW turbulence using a sub-grid model.

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On the evolution of outward and inward Alfvénic fluctuations in the polar wind

Abstract: Abstract.Plasma and magnetic field measurements by Ulysses are used to investigate the radial evolution of hourly-scale Alfv

Cited by 121 publications

References 17 publications

Particle-In-Cell simulations of circularly polarised Alfvén wave phase mixing: A new mechanism for electron acceleration in collisionless plasmas

Particle-In-Cell simulations of circularly polarised Alfvén wave phase mixing: A new mechanism for electron acceleration in collisionless plasmas

On the distribution of energy versus Alfvénic correlation for polar wind fluctuations

Heating of accretion-disk coronae and jets by general relativistic magnetohydrodynamic turbulence

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