Scaling of compressible magnetohydrodynamic turbulence in the fast solar wind

TL;DR

This study investigates how compressible fluctuations influence the energy cascade in fast solar wind turbulence, revealing that they can significantly amplify the cascade rate and contribute to energy dissipation.

Contribution

It introduces a new analysis of compressible MHD turbulence in the solar wind using an exact law, showing the significant role of compressible fluctuations in energy transfer.

Findings

Compressible fluctuations amplify the cascade rate by 2 to 4 times.

Turbulent energy cascade observed over two decades of scales.

Compressible effects are significant in 10% of the analyzed samples.

Abstract

The role of compressible fluctuations in the energy cascade of fast solar wind turbulence is studied using a reduced form of an exact law derived recently (Banerjee and Galtier, PRE, 2013) for compressible isothermal magnetohydrodynamics and in-situ observations from the THEMIS B/ARTEMIS P1 spacecraft. A statistical survey of the data revealed a turbulent energy cascade over two decades of scales, which is broader than the previous estimates made from an exact incompressible law. A term-by-term analysis of the compressible model reveals new insight into the role played by the compressible fluctuations in the energy cascade. The compressible fluctuations are shown to amplify (2 to 4 times) the turbulent cascade rate with respect to the incompressible model in 10 % of the analyzed samples. This new estimated cascade rate is shown to provide the adequate energy dissipation required.