One-point statistics and intermittency of induced electric field in the solar wind

The interplanetary induced electric field e=vxb is studied, using solar wind time series. The probability distribution functions (PDFs) of the electric field components are measured from the data and their non-gaussianity is discussed. Moreover, for the first time we show that the electric field turbulence is characterized by intermittency. This point is addressed by studying, as usual, the scaling of the PDFs of field increments, which allows a quantitative characterization of intermittency.Comment: Accepted for publication on Europhysics Letters, April 22th, 200

Turbulence, intermittency and cross-scale energy transfer in an interplanetary coronal mass ejection

Solar wind measurements carried out by NASA's Wind spacecraft before, during and after the passing of an interplanetary coronal mass ejection (ICME) detected on 12-14 September 2014 have been used in order to examine several properties of magnetohydrodynamic (MHD) turbulence. Spectral indices and flatness scaling exponents of magnetic field, velocity and proton density measurements were obtained, and provided a standard description of the characteristics of turbulence within different sub-regions of the ICME and its surroundings. This analysis was followed by the validation of the third-order moment scaling law for isotropic, incompressible MHD turbulence in the same sub-regions, which confirmed the fully developed nature of turbulence in the ICME plasma. The energy transfer rate was also estimated in each ICME sub-region and in the surrounding solar wind. An exceptionally high value was found within the ICME sheath, accompanied by enhanced intermittency, possibly related to the powerful energy injection associated with the arrival of the ICME

Ion Cyclotron Waves in Field-aligned Solar Wind Turbulence

The nature of the solar wind parallel fluctuations is investigated in this Letter by using magnetic helicity to characterize their polarization state at proton scales. Our aim is to assess the role of the proton cyclotron instability as a mechanism for generating ion cyclotron waves (ICWs) in solar wind turbulence. The wave polarization is found to depend strongly on the proton temperature anisotropy and on the power level of magnetic fluctuations at fluid scales. The results indicate a clear link between fluid and kinetic scales in the solar wind turbulence, allowing for a picture in which the resonant dissipation of high-frequency Alfvn waves heats protons in a direction perpendicular to the magnetic field, increasing their temperature anisotropy. The velocity distribution thus becomes unstable to the proton cyclotron instability, which then drives the local generation of ICWs in the solar wind

Arbitrary-order Hilbert spectral analysis and intermittency in solar wind density fluctuations

The properties of inertial and kinetic range solar wind turbulence have been investigated with the arbitrary-order Hilbert spectral analysis method, applied to high-resolution density measurements. Due to the small sample size, and to the presence of strong non-stationary behavior and large-scale structures, the classical structure function analysis fails to detect power law behavior in the inertial range, and may underestimate the scaling exponents. However, the Hilbert spectral method provides an optimal estimation of the scaling exponents, which have been found to be close to those for velocity fluctuations in fully developed hydrodynamic turbulence. At smaller scales, below the proton gyroscale, the system loses its intermittent multiscaling properties, and converges to a monofractal process. The resulting scaling exponents, obtained at small scales, are in good agreement with those of classical fractional Brownian motion, indicating a long-term memory in the process, and the absence of correlations around the spectral break scale. These results provide important constraints on models of kinetic range turbulence in the solar wind

No Evidence for Critical Balance in Field-aligned Alfvénic Solar Wind Turbulence

The properties of Alfvenic solar wind turbulence have been studied for decades using spacecraft measurements. In particular, the observation of spectral anisotropy of magnetic fluctuations has stimulated the development of several phenomenological models, one of the most popular being critical balance. However, the experimental validation of these models is intrinsically difficult because of the one-dimensional nature of the measurements provided by spacecraft instrumentation. In this work, a thorough search is performed in the Wind spacecraft database to extract samples of field-aligned fast solar wind, which allow the precise estimation of the parallel spectral properties of the magnetic fluctuations, and of their intermittency. Hilbert spectral analysis is used, in order to eliminate the possible role of nonstationarity and large-scale structures. Our results indicate that the spectral anisotropy predicted by the critical balance theory is not observed in the selected database, thus questioning the validity of the critical balance in the solar wind turbulence. A stochastic process characterized by a -5/3 spectral scaling, which is not necessarily attributed to usual turbulence, as indicated by the absence of intermittency, is indeed observed in the analyzed data samples

A Possible Link between Turbulence and Plasma Heating

Erratum: A Possible Link between Turbulence and Plasma Heating (Astrophysical Journal (2021) 921 (65) DOI: 10.3847/1538-4357/ac1942). Astrophysical Journal, Volume 923, Issue 2, 20 December 2021, Article number 282.Numerical simulations and experimental results have shown that the formation of current sheets in space plasmas can be associated with enhanced vorticity. Also, in simulations the generation of such structures is associated with strong plasma heating. Here, we compare four-point measurements in the terrestrial magnetosheath turbulence from the Magnetospheric Multiscale mission of the flow vorticity and the magnetic field curlometer versus their corresponding one-point proxies PVI(V) and PVI(B) based on the Partial Variance of Increments (PVI) method. We show that the one-point proxies are sufficiently precise in identifying not only the generic features of the current sheets and vortices statistically, but also their appearance in groups associated with plasma heating. The method has been further applied to the region of the turbulent sheath of an interplanetary coronal mass ejection (ICME) observed at L1 by the WIND spacecraft. We observe current sheets and vorticity associated heating in larger groups (blobs), which so far have not been considered in the literature on turbulent data analysis. The blobs represent extended spatial regions of activity with enhanced regional correlations between the occurrence of conditioned currents and vorticity, which at the same time are also correlated with enhanced temperatures. This heating mechanism is substantially different from the plasma heating in the vicinity of the ICME shock, where plasma beta is strongly fluctuating and there is no vorticity. The proposed method describes a new pathway for linking the plasma heating and plasma turbulence, and it is relevant to in situ observations when only single spacecraft measurements are available.Peer reviewe

Electron Heating by Kinetic Alfvén Waves in Coronal Loop Turbulence

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