Small‐Scale Energy Cascade of the Solar Wind Turbulence

Alexandrova, Olga; Carbone, V.; Veltri, P.; Sorriso‐Valvo, L.

doi:10.1086/524056

Cited by 266 publications

(314 citation statements)

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“…(27), the upper bound for the reduced intermittent amplitudes scales as B 2 thr ∝ k −2 ⊥ , and since the magnetic power spectrum in this range has shallower scaling B 2 k ∝ k −2/3 ⊥ , the flatness (and higher order normalized structure functions as well) should decrease with wavenumber in the MHD range below the first spectral kink. This can explain another interesting feature, the local decrease of the flatness in the spacecraft frequency range 0.02 ÷ 0.2 Hz (which is still below the apparent spectral kink) found by Alexandrova et al (2008a) using Cluster data. We suggest that such behavior of the flatness may indicate a partial dissipation of Alfvén waves via non-adiabatic ion acceleration in the wavenumber range where W k > W thr , illustrated in Fig.…”

Section: Non-adiabatic Threshold For Turbulent Dissipationmentioning

confidence: 69%

“…If the non-adiabatic ion acceleration and partial wave damping are active well below the apparent spectral kink, then the flatness should follow the trends as in Fig. 3 by Alexandrova et al (2008a) for Cluster data. The threshold behavior suggests that it comes into play earlier for stronger spectral fluxes; it then weakens the MHD turbulence facilitating its transition to the weak KAW turbulence with its steeper spectra.…”

Section: Spectral Formsmentioning

confidence: 78%

“…The eventual rate of the plasma heating and turbulence dissipation should follow from the balance between two processes: (i) production of the overthreshold intermittent fluctuations by the turbulence, and (ii) accommodation of turbulence energy by accelerated ions and its further redistribution into the bulk plasma. Helios observations have shown that the flatness (a measure of intermittency) increases with wavenumber (Alexandrova et al, 2008a), which progressively raises the non-adiabatic parameter above the value given by Eq. (28).…”

Section: Non-adiabatic Threshold For Turbulent Dissipationmentioning

confidence: 95%

“…There are numerous observational and theoretical indications that MHD Alfvén turbulence in the solar wind cascades towards high k ⊥ and eventually reaches the KAW wavenumber range at the proton gyroradius scales, k ⊥ ρ p ∼ 1 Bale et al, 2005;Alexandrova et al, 2008a;Sahraoui et al, 2009Sahraoui et al, , 2010. It is not yet certain what happens next with these KAWs: do they dissipate by heating the plasma , or do they interact nonlinearly among themselves and cascade further towards higher k ⊥ , ultimately reaching electron scales (Sahraoui et al, , 2010Alexandrova et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

“…For larger amplitudes and/or longer wavelengths τ NL k and τ L k become comparable, and the so-called strong turbulence in the critical balance regime is realized: τ L k τ NL k (Goldreich and Sridhar, 1995). Observations of intermittency in the inertial MHD range (Sorriso-Valvo et al, 1999;Salem et al, 2009) and in the range above the ion break (Alexandrova et al, 2008a) suggest the presence of a strongly turbulent fraction of fluctuations, but do not exclude the simultaneous presence of a weakly turbulent fraction, in particular in the MHD/kinetic transition range.…”

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confidence: 99%

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Turbulent spectra and spectral kinks in the transition range from MHD to kinetic Alfvén turbulence

Voitenko

Keyser

2011

Nonlin. Processes Geophys.

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Abstract.A weakly dispersive range (WDR) of kinetic Alfvén turbulence is identified and investigated for the first time in the context of the MHD/kinetic turbulence transition. We find perpendicular wavenumber spectra ∝ k −3 ⊥ and ∝ k −4 ⊥ formed in WDR by strong and weak turbulence of kinetic Alfvén waves (KAWs), respectively. These steep WDR spectra connect shallower spectra in the MHD and strongly dispersive KAW ranges, which results in a specific doublekink (2-k) pattern often seen in observed turbulent spectra. The first kink occurs where MHD turbulence transforms into weakly dispersive KAW turbulence; the second one is between weakly and strongly dispersive KAW ranges. Our analysis suggests that partial turbulence dissipation due to amplitude-dependent non-adiabatic ion heating may occur in the vicinity of the first spectral kink. The threshold-like nature of this process results in a conditional selective dissipation that affects only the largest over-threshold amplitudes and that decreases the intermittency in the range below the first spectral kink. Several recent counter-intuitive observational findings can be explained by the coupling between such a selective dissipation and the nonlinear interaction among weakly dispersive KAWs.

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Section: Non-adiabatic Threshold For Turbulent Dissipationmentioning

confidence: 69%

Section: Spectral Formsmentioning

confidence: 78%

Section: Non-adiabatic Threshold For Turbulent Dissipationmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Turbulent spectra and spectral kinks in the transition range from MHD to kinetic Alfvén turbulence

Voitenko

Keyser

2011

Nonlin. Processes Geophys.

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Active current sheets and candidate hot flow anomalies upstream of Mercury's bow shock

et al. 2014

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Hot flow anomalies (HFAs) represent a subset of solar wind discontinuities interacting with collisionless bow shocks. They are typically formed when the normal component of the motional (convective) electric field points toward the embedded current sheet on at least one of its sides. The core region of an HFA contains hot and highly deflected ion flows and rather low and turbulent magnetic field. In this paper, we report observations of possible HFA-like events at Mercury identified over a course of two planetary years. Using data from the orbital phase of the MESSENGER mission, we identify a representative ensemble of active current sheets magnetically connected to Mercury's bow shock. We show that some of these events exhibit magnetic and particle signatures of HFAs similar to those observed at other planets, and present their key physical characteristics. Our analysis suggests that Mercury's bow shock does not only mediate the flow of supersonic solar wind plasma but also provides conditions for local particle acceleration and heating as predicted by previous numerical simulations. Together with earlier observations of HFA activity at Earth, Venus, Mars, and Saturn, our results confirm that hot flow anomalies could be a common property of planetary bow shocks and show that the characteristic size of these events is controlled by the bow shock standoff distance and/or local solar wind conditions.

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Turbulent magnetic field fluctuations in Saturn's magnetosphere

2014

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We analyze the statistical properties of magnetic field fluctuations measured by the Cassini spacecraft inside Saturn's magnetosphere. We introduce Saturn's magnetosphere as a new laboratory for plasma turbulence, where background magnetic field is strong (1 nT = 0.07), and the ion plasma βi is smaller than one. We also show that the dissipation of these magnetic field fluctuations has important implications for the magnetosphere. In a case study of the second orbit of Cassini around Saturn we show that at MHD scales, the spectra and the nature of fluctuations are characterized by large‐scale nonstationary processes. The spectral slope varies between −0.8 and −1.7. At higher frequencies we observe a steeper spectrum with nearly constant power law exponent. A spectral break correlating with ion scales separates the two frequency ranges. We carry out a statistical study of high‐frequency range fluctuations using the first seven orbits of Cassini. We find that the energy density of raw frequency spectra depends on radial distance from Saturn and thermal and magnetic pressures. However, normalized spectra depend only on ion plasma βi. Closer to Saturn the spectral slope is about −2.3 and for radial distances r>9 Rs the average slope is −2.6. The fluctuations have probability density functions with increasingly non‐Gaussian tails and a power law increase of flatness with frequency, which indicates intermittency. We estimate the total energy flux contained in the turbulent cascade as 60–100 GW, which is on the same order of magnitude as needed to heat an adiabatically expanding plasma to the temperatures measured in Saturn's magnetosphere.

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Small‐Scale Energy Cascade of the Solar Wind Turbulence

Cited by 266 publications

References 29 publications

Turbulent spectra and spectral kinks in the transition range from MHD to kinetic Alfvén turbulence

Turbulent spectra and spectral kinks in the transition range from MHD to kinetic Alfvén turbulence

Active current sheets and candidate hot flow anomalies upstream of Mercury's bow shock

Turbulent magnetic field fluctuations in Saturn's magnetosphere

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