Kinetic scale density fluctuations in the solar wind

Chen, C. H. K.; Howes, G. G.; Bonnell, J. W.; Mozer, F. S.; Klein, K. G.; Bale, S. D.

doi:10.1063/1.4811008

Cited by 21 publications

(32 citation statements)

References 35 publications

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“…3, is observed within the same range of scales as the increase of the magnetic compressibility. The shape of this flattening is consistent with the transition between MHD scale Alfvénic turbulence and small scale KAW turbulence (Chandran et al 2009;Chen et al 2013a). More recently, Šafránková et al (2013) measured the ion density spectrum within the transition range, finding similar results, as expected from the quasi-neutrality condition.…”

Section: Turbulence Around Ion Scalessupporting

confidence: 61%

“…15 17 electron density spectra normalized in scale to the ion gyroradius, showing a flattening at ion scales ∼ (kρ i ) −1 , as in Fig. 3, and a slope close to -2.75 between ion and electron scales Chen et al (2013a) in agreement with the magnetic spectrum at these scales, see Fig. 9 The electron density spectrum between ion and electron scales was determined by Chen et al ( , 2013a using the high frequency measurements of spacecraft potential on ARTEMIS.…”

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

confidence: 51%

“…3, and a slope close to -2.75 between ion and electron scales Chen et al (2013a) in agreement with the magnetic spectrum at these scales, see Fig. 9 The electron density spectrum between ion and electron scales was determined by Chen et al ( , 2013a using the high frequency measurements of spacecraft potential on ARTEMIS. Figure 15 shows 17 electron density spectra normalized to the ion gyroradius, measured for θ BV > 45 • in the solar wind.…”

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

confidence: 52%

“…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%

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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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Section: Turbulence Around Ion Scalessupporting

confidence: 61%

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

confidence: 51%

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

confidence: 52%

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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“…Smaller values of β are associated with flattening of the power spectrum near ion scales (Chen et al, 2012b). This has been modelled as being due to two competing processes: a cascade which is passive to the Alfvénic turbulence at large scales, i.e.…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional density and compressible magnetic structure in solar wind turbulence

2018

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Abstract. The three-dimensional structure of both compressible and incompressible components of turbulence is investigated at proton characteristic scales in the solar wind. Measurements of the three-dimensional structure are typically difficult, since the majority of measurements are performed by a single spacecraft. However, the Cluster mission consisting of four spacecraft in a tetrahedral formation allows for a fully three-dimensional investigation of turbulence. Incompressible turbulence is investigated by using the three vector components of the magnetic field. Meanwhile compressible turbulence is investigated by considering the magnitude of the magnetic field as a proxy for the compressible fluctuations and electron density data deduced from spacecraft potential. Application of the multi-point signal resonator technique to intervals of fast and slow wind shows that both compressible and incompressible turbulence are anisotropic with respect to the mean magnetic field direction P ⊥ P and are sensitive to the value of the plasma beta (β; ratio of thermal to magnetic pressure) and the wind type. Moreover, the incompressible fluctuations of the fast and slow solar wind are revealed to be different with enhancements along the background magnetic field direction present in the fast wind intervals. The differences in the fast and slow wind and the implications for the presence of different wave modes in the plasma are discussed.

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Ion‐scale spectral break of solar wind turbulence at high and low beta

Chen

Leung

Boldyrev

et al. 2014

Geophysical Research Letters

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163

173

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The power spectrum of magnetic fluctuations in the solar wind at 1 AU displays a break between two power laws in the range of spacecraft-frame frequencies 0.1 to 1 Hz. These frequencies correspond to spatial scales in the plasma frame near the proton gyroradius ρi and proton inertial length di. At 1 AU it is difficult to determine which of these is associated with the break, since and the perpendicular ion plasma beta is typically β⊥i∼1. To address this, several exceptional intervals with β⊥i≪1 and β⊥i≫1 were investigated, during which these scales were well separated. It was found that for β⊥i≪1 the break occurs at di and for β⊥i≫1 at ρi, i.e., the larger of the two scales. Possible explanations for these results are discussed, including Alfvén wave dispersion, damping, and current sheets.

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Kinetic scale density fluctuations in the solar wind

Cited by 21 publications

References 35 publications

Solar Wind Turbulence and the Role of Ion Instabilities

Solar Wind Turbulence and the Role of Ion Instabilities

Three-dimensional density and compressible magnetic structure in solar wind turbulence

Ion‐scale spectral break of solar wind turbulence at high and low beta

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