Alignment and Scaling of Large-Scale Fluctuations in the Solar Wind

Wicks, Robert T.; Mallet, Alfred; Horbury, T. S.; Chen, C. H. K.; Schekochihin, A. A.; Mitchell, J. J.

doi:10.1103/physrevlett.110.025003

Cited by 48 publications

(62 citation statements)

References 39 publications

(39 reference statements)

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“…A heuristic understanding of the large interval T behavior of each of these curves is readily seen. Note that both curves show extrema for intervals around 1 h. This effect is consistent with what is shown in previous studies [Matthaeus and Goldstein, 1982a;Milano et al, 2004;Wicks et al, 2013]. For large intervals of averaging, the Alfvén ratio increases because the individual data set progressively samples more of the very energetic large-scale stream structure.…”

Section: Journal Of Geophysical Research: Space Physicssupporting

confidence: 91%

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Systematic averaging interval effects on solar wind statistics

2015

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The choice of interval of averaging in computing statistics of solar wind fluctuations is known to be a sensitive issue in which the need for adequate sampling statistics must be balanced with the complications of establishing an ensemble, given that the solar wind admits inhomogeneity, structure, and variability at its sources. Here we examine the quantitative dependence of interval of averaging (sample size) on estimates of basic statistics such as means, variances, and anisotropies of the measured interplanetary magnetic field.

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Section: Journal Of Geophysical Research: Space Physicssupporting

confidence: 91%

“…The data for these are the 64 s merged ACE MAG/SWEPAM data sets for the years 1998 through 2009. Note that both curves show extrema for intervals around 1 h. This effect has been shown in previous studies [Matthaeus and Goldstein, 1982a;Milano et al, 2004;Wicks et al, 2013].…”

Section: Correlation Time and Correlation Lengthsupporting

confidence: 85%

Systematic averaging interval effects on solar wind statistics

2015

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“…Moreover, recent results, obtained through conditioned analysis of solar wind fluctuations, have confirmed that, for high cross-helicity states, i.e. when v · b /( v 2 + b 2 ) is high, the inertial range observed in the spectrum extends to such larger scales (Wicks et al 2013). It will be interesting as well to verify the influence of the solar wind expansion time τ exp (in comparison with the non-linear time) on the extension of the inertial range (see our discussion in the introduction).…”

Section: Energy Transfer Ratementioning

confidence: 82%

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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“…Although our model describes switchbacks as the natural evolution of Alfvénic fluctuations, it is worth underlining that this does not constitute a complete explanation for the observed complex dynamics, since the physical mechanism driving and supporting solar wind fluctuations still remains a challenging open question. Nevertheless, we think that our present findings will be helpful to shed light on the origin of the solar wind low‐frequency spectrum of fluctuations and its evolution [e.g., Verdini et al , , Wicks et al , ]. More detailed analysis on the effects discussed in this work and on the possible implications for the preparation of the forthcoming space missions as Solar Orbiter and Solar Probe+ are planned.…”

Section: Resultsmentioning

confidence: 99%

Dependence of solar wind speed on the local magnetic field orientation: Role of Alfvénic fluctuations

Matteini

Horbury

Neugebauer

et al. 2014

Geophysical Research Letters

109

104

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We report an analysis of correlations between magnetic field and velocity fluctuations in the fast solar wind beyond 1 AU at high latitudes. We have found that on scales shorter than the microstream structures, there exists a well‐defined dependence of the flow speed on the angle between the magnetic field vector and the radial direction. Solar wind is found to be slightly faster when the measured magnetic field vector is transverse to the velocity, while it is always slower when the magnetic field is parallel, or antiparallel, to the radial direction. We show that this correlation is a direct consequence of the high Alfvénicity of fast wind fluctuations and that it can be reasonably described by a simple model taking into account the main properties of the low‐frequency antisunward Alfvén fluctuations as observed in the solar wind plasma. We also discuss how switchbacks, short periods of magnetic field reversals, naturally fit in this new observed correlation.

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Alignment and Scaling of Large-Scale Fluctuations in the Solar Wind

Cited by 48 publications

References 39 publications

Systematic averaging interval effects on solar wind statistics

Systematic averaging interval effects on solar wind statistics

Solar Wind Turbulence and the Role of Ion Instabilities

Dependence of solar wind speed on the local magnetic field orientation: Role of Alfvénic fluctuations

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