Constraining Ion-Scale Heating and Spectral Energy Transfer in Observations of Plasma Turbulence

Bowen, T. A.; Mallet, Alfred; Bale, S. D.; Bonnell, J. W.; Case, A. W.; Chandran, Benjamin D. G.; Chasapis, A.; Chen, Christopher H. K.; Duan, Die; Wit, T. Dudok de; Goetz, K.; Halekas, J. S.; Harvey, P.; Kasper, J. C.; Korreck, K. E.; Larson, D. E.; Livi, R.; MacDowall, R. J.; Malaspina, D.; McManus, Michael D.; Pulupa, M.; Stevens, Michael L.; Whittlesey, P. L.

doi:10.1103/physrevlett.125.025102

Cited by 41 publications

(34 citation statements)

References 88 publications

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“…We have also confirmed that the 1/4-power scaling (although not the numerical coefficient) is robust to the order of the parallel hyperdissipation (it also holds if ν 6z = 0; not shown). Spectral slopes in the ion-kinetic transition range (k ⊥ > k * ⊥ ) are seen to vary more than in the MHD range (k ⊥ < k * ⊥ ) and are very steep, α 4, in good agreement with PSP observations (Bowen et al 2020a). ⊥ above and below the break for the σ ε = 0.88 simulation of figure 5 (the averages are α ≈ 1.67 above the break and α ≈ 3.8 below the break).…”

Section: The Ion Spectral Breaksupporting

confidence: 78%

“…1 At yet smaller scales, a spectral flattening (approaching the ∼k −2.8 spectrum expected for KAW turbulence (Schekochihin et al 2009;Alexandrova et al 2009Alexandrova et al , 2012Boldyrev et al 2013)) is observed due to small leakage through the barrier (see § 3.2). The behaviour matches observations of near-Sun imbalanced turbulence from PSP, which often show clear spectral breaks significantly above the ion-Larmor scale, with a non-universal spectrum between the break and a flatter spectrum at yet smaller scales (Bowen et al 2020a;Duan et al 2021). In our theory, which differs from previous phenomenologies that assume…”

Section: Introductionsupporting

confidence: 81%

“…Thin lines show the spectra of the 256 3 imbalanced simulation at the same time and parameters (see figure 5), emphasising the re-emergence of a KAW cascade (∼k −2.8 ) at small scales in imbalanced turbulence, if a sufficient range of scales is available. The resulting double-kinked spectrum strongly resembles those observed in the solar wind (Sahraoui et al 2009;Bowen et al 2020a). As far as we know, this is the first time such spectra have been reproduced in a numerical simulation.…”

Section: Introductionsupporting

confidence: 68%

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On the violation of the zeroth law of turbulence in space plasmas

et al. 2021

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The zeroth law of turbulence states that, for fixed energy input into large-scale motions, the statistical steady state of a turbulent system is independent of microphysical dissipation properties. This behaviour, which is fundamental to nearly all fluid-like systems from industrial processes to galaxies, occurs because nonlinear processes generate smaller and smaller scales in the flow, until the dissipation – no matter how small – can thermalise the energy input. Using direct numerical simulations and theoretical arguments, we show that in strongly magnetised plasma turbulence such as that recently observed by the Parker Solar Probe spacecraft, the zeroth law is routinely violated. Namely, when such turbulence is ‘imbalanced’ – when the large-scale energy input is dominated by Alfvénic perturbations propagating in one direction (the most common situation in space plasmas) – nonlinear conservation laws imply the existence of a ‘barrier’ at scales near the ion gyroradius. This causes energy to build up over time at large scales. The resulting magnetic-energy spectra bear a strong resemblance to those observed in situ, exhibiting a sharp, steep kinetic transition range above and around the ion-Larmor scale, with flattening at yet smaller scales. The effect thus offers a possible solution to the decade-long puzzle of the position and variability of ion-kinetic spectral breaks in plasma turbulence. The existence of the ‘barrier’ also suggests that, how a plasma is forced at large scales (the imbalance) may have a crucial influence on thermodynamic properties such as the ion-to-electron heating ratio.

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Section: The Ion Spectral Breaksupporting

confidence: 78%

Section: Introductionsupporting

confidence: 81%

Section: Introductionsupporting

confidence: 68%

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On the violation of the zeroth law of turbulence in space plasmas

et al. 2021

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“…width of the magnetohydrodynamic (MHD) inertial range stays approximately constant over this distance range. The steep ionscale transition range, however, is more prominent closer to the Sun, indicating stronger dissipation or an increase in the cascade rate (Bowen et al 2020), or perhaps a build-up of energy at these scales (Meyrand et al 2020). The overall increase in the turbulence energy flux, compared to the bulk solar wind kinetic energy flux, was found by Chen et al (2020) to be consistent with the reflection-driven turbulence solar wind model of Chandran et al (2011), showing that this remains a viable mechanism to explain the acceleration of the open field wind.…”

Section: Introductionmentioning

confidence: 99%

The near-Sun streamer belt solar wind: turbulence and solar wind acceleration

Chen

Chandran

Woodham

et al. 2021

A&A

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The fourth orbit of Parker Solar Probe (PSP) reached heliocentric distances down to 27.9 R , allowing solar wind turbulence and acceleration mechanisms to be studied in situ closer to the Sun than previously possible. The turbulence properties were found to be significantly different in the inbound and outbound portions of PSP's fourth solar encounter, which was likely due to the proximity to the heliospheric current sheet (HCS) in the outbound period. Near the HCS, in the streamer belt wind, the turbulence was found to have lower amplitudes, higher magnetic compressibility, a steeper magnetic field spectrum (with a spectral index close to -5/3 rather than -3/2), a lower Alfvénicity, and a '1/ f ' break at much lower frequencies. These are also features of slow wind at 1 au, suggesting the near-Sun streamer belt wind to be the prototypical slow solar wind. The transition in properties occurs at a predicted angular distance of ≈ 4 • from the HCS, suggesting ≈ 8 • as the full-width of the streamer belt wind at these distances. While the majority of the Alfvénic turbulence energy fluxes measured by PSP are consistent with those required for reflection-driven turbulence models of solar wind acceleration, the fluxes in the streamer belt are significantly lower than the model predictions, suggesting that additional mechanisms are necessary to explain the acceleration of the streamer belt solar wind.

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“…At ion kinetic scales magnetic spectra steepen, due to some combination of dispersive and dissipative effects, leading to a sub‐ion scale energy cascade (Alexandrova et al., 2008, 2009, 2012; Sahraoui et al., 2009, 2010). Kinetic spectra with approximate k −2.7 scaling characterize the solar wind at 1 AU and the inner heliosphere (Alexandrova et al., 2012; Bowen, Mallet, Bale, et al., 2020; Chen et al., 2010; Sahraoui et al., 2009, 2013). The observed steepening is consistent with the dispersion of Alfvénic to kinetic Alfvén wave (KAW) turbulence alongside some intermittency or dissipation (Boldyrev & Perez, 2012; Chen et al., 2013; Franci et al., 2015, 2016; Howes et al., 2011; Schekochihin et al., 2009).…”

Section: Introductionmentioning

confidence: 99%

Kinetic‐Scale Turbulence in the Venusian Magnetosheath

Bowen

Bale

Bandyopadhyay

et al. 2021

Geophysical Research Letters

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Astrophysical environments are often characterized by nonlinear turbulent processes, which transfer energy from large fluid-like scales to kinetic dissipative scales. The relative accessibility of space-plasma environments has driven our understanding of these universal processes (Bruno & Carbone, 2005; Chen, 2016; Verscharen et al., 2019). While properties of large scale magnetohydrodynamic (MHD) turbulence have been studied since the earliest days of space exploration (Coleman, 1968; Matthaeus & Goldstein, 1982), relatively recent advancements in instrumentation have enabled analysis of kinetic scale turbulence (Alex

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Constraining Ion-Scale Heating and Spectral Energy Transfer in Observations of Plasma Turbulence

Cited by 41 publications

References 88 publications

On the violation of the zeroth law of turbulence in space plasmas

On the violation of the zeroth law of turbulence in space plasmas

The near-Sun streamer belt solar wind: turbulence and solar wind acceleration

Kinetic‐Scale Turbulence in the Venusian Magnetosheath

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