The Slow-Mode Nature of Compressible Wave Power in Solar Wind Turbulence

Howes, G. G.; Bale, S. D.; Klein, K. G.; Chen, C. H. K.; Salem, C. S.; TenBarge, Jason

doi:10.1088/2041-8205/753/1/l19

Cited by 151 publications

(154 citation statements)

References 26 publications

(28 reference statements)

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“…In particular, δn and δB remain predominantly anti-correlated for the slow mode and correlated for the fast mode, with a characteristic β i dependence. Howes et al (2012) compared solar wind measurements of this correlation to that produced from a critically balanced spectrum of kinetic slow waves plus an isotropic spectrum of kinetic fast waves, with different fractions of the two. The results are given in figure 6 and show a strong, β i -dependent anti-correlation, consistent with the curve in which only slow modes, and not fast modes, contribute to the compressive power.…”

Section: Nature Of the Compressive Fluctuationsmentioning

confidence: 99%

Recent progress in astrophysical plasma turbulence from solar wind observations

2016

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This paper summarises some of the recent progress that has been made in understanding astrophysical plasma turbulence in the solar wind, from in situ spacecraft observations. At large scales, where the turbulence is predominantly Alfvénic, measurements of critical balance, residual energy and three-dimensional structure are discussed, along with comparison to recent models of strong Alfvénic turbulence. At these scales, a few per cent of the energy is also in compressive fluctuations, and their nature, anisotropy and relation to the Alfvénic component is described. In the small-scale kinetic range, below the ion gyroscale, the turbulence becomes predominantly kinetic Alfvén in nature, and measurements of the spectra, anisotropy and intermittency of this turbulence are discussed with respect to recent cascade models. One of the major remaining questions is how the turbulent energy is dissipated, and some recent work on this question, in addition to future space missions which will help to answer it, are briefly discussed.

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Section: Nature Of the Compressive Fluctuationsmentioning

confidence: 99%

Recent progress in astrophysical plasma turbulence from solar wind observations

2016

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“…Howes et al (2012a) have recently argued, based on the dependence of the δB -δρ correlation on the plasma beta β (ratio of thermal to magnetic pressure), that these fluctuations are slow mode and they appear to be anisotropic in wave-vectors (He et al 2011a). measured the δB fluctuations to be more anisotropic than the Alfvénic component in the fast solar wind, suggesting this as a possible reason why they are not heavily damped (Schekochihin et al 2009).…”

Section: Density Fluctuationsmentioning

confidence: 99%

“…As with the MHD scale cascade, there are a number of observational and theoretical works, which identify turbulent fluctuations at small scales as having properties of linear wave modes (e.g., Denskat et al 1983;Goldstein et al 1994;Ghosh et al 1996;Biskamp et al 1996Biskamp et al , 1999Leamon et al 1998;Cho and Lazarian 2004;Bale et al 2005;Galtier 2006;Sahraoui et al 2010Howes et al 2006Howes et al , 2008Howes et al , 2012bSchekochihin et al 2009;Gary and Smith 2009;Chandran et al 2009;Chen et al 2010bChen et al , 2013a. A recent analysis by Chen et al (2013c) showed that the ratio of density to magnetic fluctuations in the range between ion and electron scales is very close to that expected for kinetic Alfvén waves, and not whistler waves, and concluded that the fluctuations in this range are predominantly strong kinetic Alfvén turbulence.…”

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

confidence: 99%

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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“…Their work also indicated the existence of small pressure-balanced structures with different sizes (typically up to some 100 s in time scale) in the solar wind. Howes et al (2012) used statistical analysis of Wind data to demonstrate that the compressible fluctuations in the inertial range were consistent with being due almost entirely to slow mode fluctuations. Some time ago, Marsch & Tu (1993) and Tu & Marsch (1994) established, on the basis of Helios data, the prevalence of a slow mode at inertial-range scales in the compressive component of solar wind turbulence.…”

Section: Revisiting Slow Modementioning

confidence: 99%

Kinetic Slow Mode in the Solar Wind and Its Possible Role in Turbulence Dissipation and Ion Heating

Narita

Marsch

2015

ApJ

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The solar wind is permeated by various kinds of fluctuations ranging broadly in scales from those of the solar corona and inner heliosphere down to the local ion and electron plasma kinetic scales. The question of what rules the dissipation of magnetohydrodynamic (MHD) turbulence in the solar wind has not conclusively been answered, but remains a key research topic of space plasma physics. Here we propose a new dissipation mechanism, the proton Landau damping of the quasi-perpendicular kinetic slow mode. This mode is linked to the oblique MHD slow mode, yet has shorter wavelengths going down to the proton inertial length. The kinetic slow mode can be separated from the kinetic Alfvén mode by the Alfvén resonance parameter, the proton Landau resonance parameter, the magnetic compressibility, and the electric field polarization. Numerical simulations and in situ observations indicate that the MHD turbulent cascade preferably transfers energy in the direction perpendicular to the background magnetic field. If the kinetic slow mode is also generated and replenished by the energy cascade, this mode can lead to both perpendicular and parallel heating of the protons.

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The Slow-Mode Nature of Compressible Wave Power in Solar Wind Turbulence

Cited by 151 publications

References 26 publications

Recent progress in astrophysical plasma turbulence from solar wind observations

Recent progress in astrophysical plasma turbulence from solar wind observations

Solar Wind Turbulence and the Role of Ion Instabilities

Kinetic Slow Mode in the Solar Wind and Its Possible Role in Turbulence Dissipation and Ion Heating

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