Turbulent Density Spectrum in Solar Wind Plasma

TL;DR

This paper demonstrates through 3D simulations that a Kolmogorov-like density spectrum in the solar wind arises mainly from Alfvénic cascades, despite the plasma's compressibility, addressing a key turbulence paradox.

Contribution

The study provides the first detailed numerical evidence that Alfvénic turbulence can produce a Kolmogorov-like density spectrum in compressible magnetized plasma.

Findings

Density spectrum follows a -5/3 slope in simulations.

Alfvénic cascades dominate energy transfer.

Compressible modes are dissipated.

Abstract

The density fluctuation spectrum in the solar wind reveals a Kolmogorov-like scaling with a spectral slope of -5/3 in wavenumber space. The energy transfer process in the magnetized solar wind, characterized typically by MHD turbulence, over extended length-scales remains an unresolved paradox of modern turbulence theories, raising the question of how a compressible magnetofluid exhibits a turbulent spectrum that is 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 fluid. It is shown that a Kolmogorov-like density spectrum can develop by plasma motions that are dominated by Alfv\'enic cascades whereas compressive modes are dissipated.