Scaling Laws of Turbulence and Heating of Fast SolarWind: The Role of Density Fluctuations

TL;DR

This paper investigates the scaling laws of turbulence and heating in the fast solar wind, emphasizing the significant role of density fluctuations in energy transfer and dissipation processes.

Contribution

It introduces a modified scaling law accounting for compressible fluctuations, highlighting the impact of density fluctuations on turbulence and solar wind heating.

Findings

Density fluctuations influence turbulence scaling laws.

Compressible turbulence can supply energy for solar wind heating.

Modified scaling laws better match observational data.

Abstract

Incompressible and isotropic magnetohydrodynamic turbulence in plasms can be described by an exact relation for the energy flux through the scales. This Yaglom-like scaling law has been recently observed in the solar wind above the solar poles observed by the Ulysses spacecraft, where the turbulence is in an Alfv\'enic state. An analogous phenomenological scaling law, suitably modified to take into account compressible fluctuations, is observed more frequently in the same dataset. Large scale density fluctuations, despite their low amplitude, play thus a crucial role in the basic scaling properties of turbulence. The turbulent cascade rate in the compressive case can moreover supply the energy dissipation needed to account for the local heating of the non-adiabatic solar wind.