Abstract
In weakly collisional space plasmas, the turbulent cascade provides most of the energy that is dissipated at small scales by various kinetic processes. Understanding the characteristics of such dissipative mechanisms requires the accurate knowledge of the fluctuations that make energy available for conversion at small scales, as different dissipation processes are triggered by fluctuations of a different nature. The scaling properties of different energy channels are estimated here using a proxy of the local energy transfer, based on the third-order moment scaling law for magnetohydrodynamic turbulence. In particular, the sign-singularity analysis was used to explore the scaling properties of the alternating positive-negative energy fluxes, thus providing information on the structure and topology of such fluxes for each of the different type of fluctuations. The results show the highly complex geometrical nature of the flux, and that the local contributions associated with energy and cross-helicity nonlinear transfer have similar scaling properties. Consequently, the fractal properties of current and vorticity structures are similar to those of the Alfv\'enic fluctuations.
Highlights
The dynamics of space plasmas is characterized by a broad variety of complex processes that include turbulence, instabilities, and several mechanisms of particle-radiation interaction
In the fast solar wind sample measured by Wind, the scaling exponent of the total energy transfer proxy near the bottom of the inertial range ( t = 6s) is κ ∼ 1/4, which corresponds to the presence of structures of fractal dimension D ∼ 0.5
This is in agreement with the typical observation of disrupted current sheets of solar wind intermittent turbulence [63], and confirms the fact that the turbulence is well developed in this fast wind stream, with strong intermittency
Summary
The dynamics of space plasmas is characterized by a broad variety of complex processes that include turbulence, instabilities, and several mechanisms of particle-radiation interaction. Such processes are intrinsically connected across multiple scales. Theoretical efforts are being carried out in order to highlight the specific processes governing the energy exchange between ranges associated to different regimes [25,26,27] In this framework, the local, fine-scale details of the turbulent energy cascade acquire new importance, as the specific characteristics of the fluctuations carrying energy to the kinetic scales can be associated with different plasma processes [11, 28, 29]
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