Long- and Short-Term Evolutions of Magnetic Field Fluctuations in High-Speed Streams

Pi, Gilbert; Pitňa, Alexander; Němeček, Zdenek; Šafránková, Jana; Shue, J.‐H.; Yang, Ya Hui

doi:10.1007/s11207-020-01646-8

Cited by 9 publications

(7 citation statements)

References 35 publications

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“…A similar trend was observed with σ r and V sw , not shown here. The results are consistent with(Vasquez et al 2007), who found higher, MHD range, turbulence amplitudes associated with faster streams, as well as,(Pi et al 2020) who showed that such dependence vanishes in the kinetic scales. The trend also vanishes at the large, energy injection scales, κd i ≤ 10 −3 , where the power spectrum is clearly dominated by parallel fluctuations.…”

supporting

confidence: 90%

On the evolution of the Anisotropic Scaling of Magnetohydrodynamic Turbulence in the Inner Heliosphere

Sioulas¹,

Velli²,

Huang³

et al. 2023

Preprint

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We analyze a merged Parker Solar Probe (P SP ) and Solar Orbiter (SO) dataset covering heliocentric distances 13 R R 220 R to investigate the radial evolution of power and spectral-index anisotropy in the wavevector space of solar wind turbulence. Our results show that anisotropic signatures of turbulence display a distinct radial evolution when fast, V sw ≥ 400 km s −1 , and slow, V sw ≤ 400 km s −1 , wind streams are considered. The anisotropic properties of slow wind in Earth orbit are consistent with a "critically balanced" cascade, but both spectral-index anisotropy and power

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supporting

confidence: 90%

On the evolution of the Anisotropic Scaling of Magnetohydrodynamic Turbulence in the Inner Heliosphere

Sioulas¹,

Velli²,

Huang³

et al. 2023

Preprint

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show abstract

“…A similar trend was observed with σ r and V sw , not shown here. The results are consistent with Vasquez et al (2007), who found higher, MHD range, turbulence amplitudes associated with faster streams, as well as Pi et al (2020), who showed that such dependence vanishes in the kinetic scales. The trend also vanishes at the large, energy injection scales, κd i 10 −3 , where || ( ) .…”

Section: Case Study: Scam Data Set E1supporting

confidence: 90%

On the Evolution of the Anisotropic Scaling of Magnetohydrodynamic Turbulence in the Inner Heliosphere

Sioulas

Velli

Huang

et al. 2023

ApJ

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We analyze a merged Parker Solar Probe (PSP) and Solar Orbiter (SO) data set covering heliocentric distances 13 R ⊙ ≲ R ≲ 220 R ⊙ to investigate the radial evolution of power and spectral index anisotropy in the wavevector space of solar wind turbulence. Our results show that anisotropic signatures of turbulence display a distinct radial evolution when fast, V sw ≥ 400 km s−1, and slow, V sw ≤ 400 km s−1, wind streams are considered. The anisotropic properties of slow wind in Earth orbit are consistent with a “critically balanced” cascade, but both spectral index anisotropy and power anisotropy diminish with decreasing heliographic distance. Fast streams are observed to roughly retain their near-Sun anisotropic properties, with the observed spectral index and power anisotropies being more consistent with a “dynamically aligned” type of cascade, though the lack of extended fast wind intervals makes it difficult to accurately measure the anisotropic scaling. A high-resolution analysis during the first perihelion of PSP confirms the presence of two subranges within the inertial range, which may be associated with the transition from weak to strong turbulence. The transition occurs at κ d i ≈ 6 × 10−2 and signifies a shift from −5/3 to −2 and from −3/2 to −1.57 scaling in parallel and perpendicular spectra, respectively. Our results provide strong observational constraints for anisotropic theories of MHD turbulence in the solar wind.

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“…Recent PSP observations [24,26] of a young solar wind suggest that the level normalized cross-helicity (imbalance between the counter-propagating Alfvén wave packets) may play a role in the dynamics of the transitional range, which may lead to the observed steepening. Huang et al [26] reported a weak anticorrelation between the transition range spectral index and cross-helicity, in relative terms, such a trend is qualitatively consistent with Figure 8 because higher levels of inertial range fluctuations are characteristic for fast solar wind [52], which exhibits non-zero cross-helicity. We plan to address the role of cross-helicity in a future study that will employ hybrid-kinetic simulations and the technique introduced in the current manuscript.…”

Section: Discussionsupporting

confidence: 72%

A Novel Method for Estimating the Intrinsic Magnetic Field Spectrum of Kinetic-Range Turbulence

et al. 2021

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Understanding plasma turbulence below the ion characteristic scales is one of the key open problems of solar wind physics. The bulk of our knowledge about the nature of the kinetic-scale fluctuations comes from the high-cadence measurements of the magnetic field. The spacecraft frame frequencies of the sub-ion scale fluctuations are frequently around the Nyquist frequencies of the magnetic field sampling rate. Thus, the resulting ‘measured’ time series may significantly differ from the ‘true’ ones. It follows that second-order moments (e.g., power spectral density, PSD) of the signal may also be highly affected in both their amplitude and their slope. In this paper, we focus on the estimation of the PSD slope for finitely sampled data and we unambiguously define a so-called local slope in the framework of Continuous Wavelet Transform. Employing Monte Carlo simulations, we derive an empirical formula that assesses the statistical error of the local slope estimation. We illustrate the theoretical results by analyzing measurements of the magnetic field instrument (MFI) on board the Wind spacecraft. Our analysis shows that the trace power spectra of magnetic field measurements of MFI can be modeled as the sum of PSD of an uncorrelated noise and an intrinsic signal. We show that the local slope strongly depends on the signal-to-noise (S/N) ratio, stressing that noise can significantly affect the slope even for S/N around 10. Furthermore, we show that the local slopes below the frequency corresponding to proton inertial length, 5≳kλpi>1, depend on the level of the magnetic field fluctuations in the inertial range (Pin), exhibiting a gradual flattening from about −11/3 for high Pin toward about −8/3 for low Pin.

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Long- and Short-Term Evolutions of Magnetic Field Fluctuations in High-Speed Streams

Cited by 9 publications

References 35 publications

On the evolution of the Anisotropic Scaling of Magnetohydrodynamic Turbulence in the Inner Heliosphere

On the evolution of the Anisotropic Scaling of Magnetohydrodynamic Turbulence in the Inner Heliosphere

On the Evolution of the Anisotropic Scaling of Magnetohydrodynamic Turbulence in the Inner Heliosphere

A Novel Method for Estimating the Intrinsic Magnetic Field Spectrum of Kinetic-Range Turbulence

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