Abstract:Aims. A linear scaling of the mixed third-order moment of the magnetohydrodynamic (MHD) fluctuations is used to estimate the energy transfer rate of the turbulent cascade in the expanding solar wind.
Methods. In 1976, the Helios 2 spacecraft measured three samples of fast solar wind originating from the same coronal hole, at different distances from the Sun. Along with the adjacent slow solar wind streams, these intervals represent a unique database for studying the radial evolution of turbulence in samples of… Show more
“…More refined estimates of radial variations can be found in the literature (e.g., Chhiber et al 2021). The same scaling was also observed by using a multi-spacecraft study following the same solar wind plasma at two different distances (Sorriso-Valvo et al 2023).…”
A central problem of space plasma physics is how protons and electrons are heated in a turbulent, magnetized plasma. The differential heating of charged species due to dissipation of turbulent fluctuations plays a key role in solar wind evolution. Measurements from previous heliophysics missions have provided estimates of proton and electron heating rates beyond 0.27 au. Using Parker Solar Probe (PSP) data accumulated during the first 10 encounters, we extend the evaluation of the individual rates of heat deposition for protons and electrons to a distance of 0.063 au (13.5 R
⊙) in the newly formed solar wind. The PSP data in the near-Sun environment show different behavior of the electron heat conduction flux from what was predicted from previous fits to Helios and Ulysses data. Consequently, the empirically derived proton and electron heating rates exhibit significantly different behavior than previous reports, with the proton heating becoming increasingly dominant over electron heating at decreasing heliocentric distances. We find that the protons receive about 80% of the total plasma heating at ≈13 R
⊙, slightly higher than the near-Earth values. This empirically derived heating partition between protons and electrons will help to constrain theoretical models of solar wind heating.
“…More refined estimates of radial variations can be found in the literature (e.g., Chhiber et al 2021). The same scaling was also observed by using a multi-spacecraft study following the same solar wind plasma at two different distances (Sorriso-Valvo et al 2023).…”
A central problem of space plasma physics is how protons and electrons are heated in a turbulent, magnetized plasma. The differential heating of charged species due to dissipation of turbulent fluctuations plays a key role in solar wind evolution. Measurements from previous heliophysics missions have provided estimates of proton and electron heating rates beyond 0.27 au. Using Parker Solar Probe (PSP) data accumulated during the first 10 encounters, we extend the evaluation of the individual rates of heat deposition for protons and electrons to a distance of 0.063 au (13.5 R
⊙) in the newly formed solar wind. The PSP data in the near-Sun environment show different behavior of the electron heat conduction flux from what was predicted from previous fits to Helios and Ulysses data. Consequently, the empirically derived proton and electron heating rates exhibit significantly different behavior than previous reports, with the proton heating becoming increasingly dominant over electron heating at decreasing heliocentric distances. We find that the protons receive about 80% of the total plasma heating at ≈13 R
⊙, slightly higher than the near-Earth values. This empirically derived heating partition between protons and electrons will help to constrain theoretical models of solar wind heating.
“…Subsequently, a maximum is reached at scales compatible with the typical transition region observed between the MHD and kinetic scales [42,43]. The fitting power law exponents, listed in Table 2, are consistent with previous observations in the solar wind (e.g., see [44]). On the contrary, by computing the purely anisotropic kurtosis, we found stronger intermittency to be associated with anisotropic fluctuations (see the values of the scaling exponents κ αβ reported in Table 2).…”
Section: Global Correlation Tensor Analysissupporting
Space plasma turbulence is inherently characterized by anisotropic fluctuations. The generalized k-th order correlation tensor of magnetic field increments allow us to separate the mixed isotropic and anisotropic structure functions from the purely anisotropic ones. In this work, we quantified the relative importance of anisotropic fluctuations in solar wind turbulence using two Alfvénic data samples gathered by the Solar Orbiter at 0.8 astronomical units. The results based on the joined statistics suggest that the anisotropic fluctuations are ubiquitous in solar wind turbulence and persist at kinetic scales. Using the RTN coordinate system, we show that their presence depends on the anisotropic sector under consideration, e.g., the RN and RT sectors exhibit enhanced anisotropy toward kinetic scales, in contrast with the TN. We then study magnetic field fluctuations parallel and perpendicular to the local mean magnetic field separately. We find that perpendicular fluctuations are representative of the global statistics, resembling the typical picture of magnetohydrodynamic turbulence, whereas parallel fluctuations exhibit a scaling law with slope ∼1 for all the joined isotropic and anisotropic components. These results are in agreement with predictions based on the critical balance phenomenology. This topic is potentially of interest for future space missions measuring kinetic and MHD scales simultaneously in a multi-spacecraft configuration.
“…However, characterizing their contribution to the plasma energetics among other plasma processes is a challenging task, for which it is important to run highly accurate 3-D Hall-MHD numerical simulations, able to resolve an extended dynamical range with the largest possible scale separation. A first implementation of FLAME aiming at demonstrating the decaying nature of solar wind turbulence has been presented by Sorriso-Valvo et al (2023), where a direct comparison between the simulated fields and the observations performed by the Helios 2 spacecraft is proposed, showing very good agreement.…”
Section: Hall-mhd Simulations For Space Plasma Turbulence Investigationsmentioning
confidence: 99%
“…A first implementation of flame aiming at demonstrating the decaying nature of solar wind turbulence has been presented by Sorriso-Valvo et al. (2023), where a direct comparison between the simulated fields and the observations performed by the Helios 2 spacecraft is proposed, showing very good agreement. Figure 17.Power spectra density (PSD) of the magnetic field fluctuations observed by PSP (red) and SO (blue) on November , and July 14–15, , respectively.…”
Section: Hall-mhd Simulations For Space Plasma Turbulence Investigationsmentioning
Simulating plasmas in the Hall-magnetohydrodynamics (Hall-MHD) regime represents a valuable approach for the investigation of complex nonlinear dynamics developing in astrophysical frameworks and fusion machines. The Hall electric field is computationally very challenging as it involves the integration of an additional term, proportional to
$\boldsymbol {\nabla } \times ((\boldsymbol {\nabla }\times \boldsymbol {B})\times \boldsymbol {B})$
, in Faraday's induction law. The latter feeds back on the magnetic field
$B$
at small scales (between the ion and electron inertial scales), requiring very high resolutions in both space and time to properly describe its dynamics. The computational advantage provided by the kinetic lattice Boltzmann (LB) approach is exploited here to develop a new code, the fast lattice-Boltzmann algorithm for MHD experiments (flame). The flame code integrates the plasma dynamics in lattice units coupling two kinetic schemes, one for the fluid protons (including the Lorentz force), the other to solve the induction equation describing the evolution of the magnetic field. Here, the newly developed algorithm is tested against an analytical wave-solution of the dissipative Hall-MHD equations, pointing out its stability and second-order convergence, over a wide range of the control parameters. Spectral properties of the simulated plasma are finally compared with those obtained from numerical solutions from the well-established pseudo-spectral code ghost. Furthermore, the LB simulations we present, varying the Hall parameter, highlight the transition from the MHD to the Hall-MHD regime, in excellent agreement with the magnetic field spectra measured in the solar wind.
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