| 1. |
- Alberti, Tommaso, et al.
(författare)
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Multifractal and Chaotic Properties of Solar Wind at MHD and Kinetic Domains : An Empirical Mode Decomposition Approach
- 2019
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Ingår i: Entropy. - : MDPI AG. - 1099-4300. ; 21:3
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Tidskriftsartikel (refereegranskat)abstract
- Turbulence, intermittency, and self-organized structures in space plasmas can be investigated by using a multifractal formalism mostly based on the canonical structure function analysis with fixed constraints about stationarity, linearity, and scales. Here, the Empirical Mode Decomposition (EMD) method is firstly used to investigate timescale fluctuations of the solar wind magnetic field components; then, by exploiting the local properties of fluctuations, the structure function analysis is used to gain insights into the scaling properties of both inertial and kinetic/dissipative ranges. Results show that while the inertial range dynamics can be described in a multifractal framework, characterizing an unstable fixed point of the system, the kinetic/dissipative range dynamics is well described by using a monofractal approach, because it is a stable fixed point of the system, unless it has a higher degree of complexity and chaos.
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| 2. |
- Benella, Simone, et al.
(författare)
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Kramers-Moyal analysis of interplanetary magnetic field fluctuations at sub-ion scales
- 2022
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Ingår i: Rendiconti Lincei SCIENZE FISICHE E NATURALI. - : Springer Nature. - 2037-4631 .- 1720-0776. ; 33:4, s. 721-728
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Tidskriftsartikel (refereegranskat)abstract
- In the framework of statistical time series analysis of complex dynamics, we present a multiscale characterization of solar wind turbulence in the near-earth environment. The data analysis, based on the Markov process theory, is meant to estimate the Kramers-Moyal coefficients associated with the measured magnetic field fluctuations. In fact, when the scale-to-scale dynamics can be successfully described as a Markov process, first- and second-order Kramers-Moyal coefficients provide a complete description of the dynamics in terms of Langevin stochastic process. The analysis is carried out using high-resolution magnetic field measurements gathered by Cluster during a fast solar wind period on January 20, 2007. This analysis extends recent findings in the near-Sun environment with the aim of testing the universality of the Markovian nature of the magnetic field fluctuations in the sub-ion/kinetic domain.
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| 3. |
- Benella, Simone, et al.
(författare)
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Linking the Langevin equation to scaling properties of space plasma turbulence at sub-ion scales
- 2023
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Ingår i: Physical Review Research. - : American Physical Society. - 2643-1564. ; 5:4
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Tidskriftsartikel (refereegranskat)abstract
- Current understanding of the kinetic-scale turbulence in weakly collisional plasmas still remains elusive. We employ a general framework in which the turbulent energy transfer is envisioned as a scale-to-scale Langevin process. Fluctuations in the sub-ion range show a global scale invariance, thus suggesting a homogeneous energy repartition. In this Letter, we interpret such a feature by linking the drift term of the Langevin equation to scaling properties of fluctuations. Theoretical expectations are verified on solar wind observations and numerical simulations, thus giving relevance to the proposed framework for understanding kinetic-scale turbulence in space plasmas.
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| 4. |
- Carbone, Francesco, et al.
(författare)
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Local dimensionality and inverse persistence analysis of atmospheric turbulence in the stable boundary layer
- 2022
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Ingår i: Physical review. E. - : American Physical Society. - 2470-0045 .- 2470-0053. ; 106:6
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics across different scales in the stable atmospheric boundary layer has been investigated by means of two metrics, based on instantaneous fractal dimensions and grounded in dynamical systems theory. The wind velocity fluctuations obtained from data collected during the Cooperative Atmosphere-Surface Exchange Study- 1999 experiment were analyzed to provide a local (in terms of scales) and an instantaneous (in terms of time) description of the fractal properties and predictability of the system. By analyzing the phase-space projections of the continuous turbulent, intermittent, and radiative regimes, a progressive transformation, characterized by the emergence of multiple low-dimensional clusters embedded in a high-dimensional shell and a two-lobe mirror symmetrical structure of the inverse persistence, have been found. The phase space becomes increasingly complex and anisotropic as the turbulent fluctuations become uncorrelated. The phase space is characterized by a three-dimensional structure for the continuous turbulent samples in a range of scales compatible with the inertial subrange, where the phase-space-filling turbulent fluctuations dominate the dynamics, and is low dimensional in the other regimes. Moreover, lower-dimensional structures present a stronger persistence than the higher-dimensional structures. Eventually, all samples recover a three-dimensional structure and higher persistence level at large scales, far from the inertial subrange. The two metrics obtained in the analysis can be considered as proxies for the decorrelation time and the local anisotropy in the turbulent flow.
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| 5. |
- Voeroes, Zoltan, et al.
(författare)
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Turbulence-Generated Proton-Scale Structures In The Terrestrial Magnetosheath
- 2016
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Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 819:1
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Tidskriftsartikel (refereegranskat)abstract
- Recent results of numerical magnetohydrodynamic simulations suggest that in collisionless space plasmas, turbulence can spontaneously generate thin current sheets. These coherent structures can partially explain the intermittency and the non-homogenous distribution of localized plasma heating in turbulence. In this Letter, Cluster multi-point observations are used to investigate the distribution of magnetic field discontinuities and the associated small-scale current sheets in the terrestrial magnetosheath downstream of a quasi-parallel bow shock. It is shown experimentally, for the first time, that the strongest turbulence-generated current sheets occupy the long tails of probability distribution functions associated with extremal values of magnetic field partial derivatives. During the analyzed one-hour time interval, about a hundred strong discontinuities, possibly proton-scale current sheets, were observed.
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