Power Spectral Density of Fluctuations of Bulk and Thermal Speeds in the Solar Wind

Šafránková, Jana; Němeček, Zdenek; Němec, F.; Přech, Lubomír; Chen, C. H. K.; Zastenker, G. N.

doi:10.3847/0004-637x/825/2/121

Cited by 48 publications

(36 citation statements)

References 35 publications

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“…The results for the V A spectrum are consistent with those often found in the solar wind for the magnetic field, being close to the Kolmogorov −5/3 power law at inertial scales before steepening after the spectral break (e.g., Bruno et al, ; Smith et al, ). Meanwhile, velocity spectrum is flatter at inertial scales before steepening more prominently after the spectral break again similarly to the solar wind case (Šafránková et al, , ).…”

Section: Datamentioning

confidence: 61%

Ion‐Scale Kinetic Alfvén Turbulence: MMS Measurements of the Alfvén Ratio in the Magnetosheath

Roberts

Toledo‐Redondo

Perrone

et al. 2018

Geophysical Research Letters

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Turbulence in the Earth's magnetosheath at ion kinetic scales is investigated with the magnetospheric multiscale spacecraft. Several possibilities in the wave paradigm have been invoked to explain plasma turbulence at ion kinetic scales such as kinetic Alfvén, slow, or magnetosonic waves. To differentiate between these different plasma waves is a challenging task, especially since some waves, in particular, kinetic slow waves and kinetic Alfvén waves, share some properties making the possibility to distinguishing between them very difficult. Using the excellent time resolution data set provided from both the fluxgate magnetometer and the Fast Plasma Instrument, the ratio of trace velocity fluctuations to the magnetic fluctuations (in Alfvén units), which is termed the Alfvén ratio, can be calculated down to ion kinetic scales. Comparison of the measured Alfvén ratio is performed with respect to the expectation from two‐fluid magnetohydrodynamic theory for the kinetic slow wave and kinetic Alfvén wave. Moreover, the plasma data also allow normalized fluctuation amplitudes of density and magnetic field to be compared differentiating between magnetosonic‐like and kinetic Alfvén‐like turbulence. Using these two different ratios, we can rule out that the fluctuations at ion scales are dominated by magnetosonic‐like fluctuations or kinetic slow‐like fluctuations and show that they are consistent with kinetic Alfvén‐like fluctuations. This suggests that in the wave paradigm, heating in the direction of the parallel magnetic field is predominantly by the Landau damping of the kinetic Alfvén wave.

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Section: Datamentioning

confidence: 61%

Ion‐Scale Kinetic Alfvén Turbulence: MMS Measurements of the Alfvén Ratio in the Magnetosheath

Roberts

Toledo‐Redondo

Perrone

et al. 2018

Geophysical Research Letters

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“…Alexandrova et al 2009;Sahraoui et al 2013). More recently, we have also been able to measure the density spectrum in this range (Chen et al 2012b;Šafránková et al 2013. Chen et al (2012b) showed that this also takes a powerlaw form, with a spectral index of −2.75 ± 0.06, similar to the magnetic spectrum.…”

Section: Phenomenological Models Of Kinetic Range Turbulencementioning

confidence: 87%

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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“…Prolonged interval (2,048 s) was used in this case for valid determination of the slope at MHD scales. Šafránková et al (, ) showed the correlation between the second break of the spectra with plateau and plasma characteristic frequencies. For spectra of this type the frequency of the second break was chosen for further analysis.…”

Section: Methodsmentioning

confidence: 99%

“…Kinetic‐scale plasma fluctuations have been explored systematically since 2011 with the help of the BMSW (Fast Solar Wind Monitor, Šafránková, Němeček, Přech, Zastenker, Cěrmák, et al, ; Zastenker et al, ) instrument on board Spektr‐R spacecraft. Parameters of plasma turbulence based on BMSW measurements were considered in the SW (Chen et al, ; Riazantseva et al, , , ; Šafránková, Němeček, Přech, & Zastenker, ; Šafránková et al, , ) as well as in the flank MSH (Rakhmanova et al, ; Rakhmanova, Riazantseva, Zastenker & Yermolaev, ; Riazantseva et al, , ). The BMSW data set covers 6 years of continuous plasma measurements in the SW and MSH that allow for statistical study of plasma fluctuations for various ambient conditions and upstream SW parameters.…”

Section: Introductionmentioning

confidence: 99%

Kinetic‐Scale Ion Flux Fluctuations Behind the Quasi‐Parallel and Quasi‐Perpendicular Bow Shock

et al. 2018

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Properties of kinetic‐scale plasma turbulence are examined observationally with the help of Spektr‐R measurements in the Earth's magnetosheath. The statistics covers 6 years of ion flux measurements during years 2011–2017 and includes a few dozens of the magnetosheath crossings with total duration of 250 hr. Several types of Fourier spectra are distinguished in the magnetosheath according to a spectral shape at the scales of transition from magnetohydrodynamic to kinetic regimes. Spectral indices and occurrence rate of different spectral shapes are examined at different locations with respect to the magnetosheath boundaries—the magnetopause and the bow shock. Magnetosheath plasma behind the quasi‐parallel and quasi‐perpendicular bow shock is explored separately. Clear dynamics of spectral shapes across the magnetosheath is shown: spectra with broad bump at the transition frequencies occur more frequently in the vicinity of the bow shock, while spectra with plateau at the same frequencies are usually observed closer to the magnetopause. Spectral indices such as spectral slope at the kinetic scales and break frequency are shown to be weakly affected by the boundaries behind the quasi‐perpendicular bow shock. The steepest spectra are observed close to the quasi‐parallel bow shock.

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Power Spectral Density of Fluctuations of Bulk and Thermal Speeds in the Solar Wind

Cited by 48 publications

References 35 publications

Ion‐Scale Kinetic Alfvén Turbulence: MMS Measurements of the Alfvén Ratio in the Magnetosheath

Ion‐Scale Kinetic Alfvén Turbulence: MMS Measurements of the Alfvén Ratio in the Magnetosheath

Recent progress in astrophysical plasma turbulence from solar wind observations

Kinetic‐Scale Ion Flux Fluctuations Behind the Quasi‐Parallel and Quasi‐Perpendicular Bow Shock

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