Turbulent Spectra in the Solar Wind Plasma

TL;DR

This paper demonstrates through 3D simulations that the Kolmogorov-like turbulent spectrum observed in the solar wind can arise from supersonic plasma motions that transition into subsonic flows, passively convecting density fluctuations.

Contribution

The study provides a numerical explanation for the Kolmogorov-like spectrum in solar wind plasma using compressible MHD simulations of super-Alfvénic, supersonic flows.

Findings

Kolmogorov-like (-5/3) spectrum develops in simulations

Supersonic motions dissipate into subsonic flows

Density fluctuations are passively convected

Abstract

Observations of interstellar scintillations at radio wavelengths reveal a Kolmogorov-like scaling of the electron density spectrum with a spectral slope of -5/3 over six decades in wavenumber space. A similar turbulent density spectrum in the solar wind plasma has been reported. The energy transfer process in the magnetized solar wind plasma over such extended length-scales remains an unresolved paradox of modern turbulence theories raising the especially intriguing question of how a compressible magnetized solar wind exhibits a turbulent spectrum that is a characteristic of an incompressible hydrodynamic fluid. To address these questions, we have undertaken three-dimensional time dependent numerical simulations of a compressible magnetohydrodynamic fluid describing super-Alfv\'enic, supersonic and strongly magnetized plasma. It is shown that the observed Kolmogorov-like (-5/3) spectrum can develop in the solar wind plasma by supersonic plasma motions that dissipate into highly subsonic motion that passively convect density fluctuations.