Kinetic turbulence in space plasmas observed in the near-Earth and near-Sun solar wind

TL;DR

This paper investigates kinetic turbulence in space plasmas, revealing a universal magnetic spectrum at different solar distances and characterizing the fluctuations as non-linear eddies forming magnetic filaments.

Contribution

It demonstrates the universality of the kinetic turbulence spectrum across various solar distances and characterizes the nature of the fluctuations as non-linear eddies.

Findings

Magnetic spectra at different solar distances are similar.

Fluctuations are non-linearly interacting eddies.

Eddies tend to generate magnetic filaments.

Abstract

Turbulence develops in any stressed flow when the scales of the forcing are much larger than those of the dissipation. In neutral fluids, it consists of chaotic motions in physical space but with a universal energy spectrum in Fourier space. Intermittency (non-Gaussian statistics of fluctuations) is another general property and it is related to the presence of coherent structures. Space plasmas are turbulent as well. Here, we focus on the kinetic plasma scales, which are not yet well understood. We address the following fundamental questions: (1) Do the turbulent fluctuations at kinetic scales form a universal spectrum? and (2) What is the nature of the fluctuations? Using measurements in the solar wind we show that the magnetic spectra of kinetic turbulence at 0.3, 0.6 and 0.9 AU from the Sun have the same shape as the ones close to the Earth orbit at 1 AU, indicating universality of the phenomenon. The fluctuations, which form this spectrum, are typically non-linearly interacting eddies that tend to generate magnetic filaments.