Three-Dimensional Structure of Solar Wind Turbulence

TL;DR

This study investigates the three-dimensional anisotropic structure of magnetic field fluctuations in solar wind turbulence, revealing scale-dependent anisotropy and insights into the nature of Alfvenic and compressive fluctuations.

Contribution

It provides the first detailed measurement of the 3D anisotropic structure of solar wind turbulence with respect to a local coordinate system, highlighting scale-dependent anisotropy variations.

Findings

Alfvenic fluctuations are 3D anisotropic, varying from large to small scales.

At the outer scale, correlations are longest in the fluctuation direction, consistent with Alfven waves.

Compressive fluctuations are highly elongated along the local mean magnetic field.

Abstract

We present a measurement of the scale-dependent, three-dimensional structure of the magnetic field fluctuations in inertial range solar wind turbulence with respect to a local, physically motivated coordinate system. The Alfvenic fluctuations are three-dimensionally anisotropic, with the sense of this anisotropy varying from large to small scales. At the outer scale, the magnetic field correlations are longest in the local fluctuation direction, consistent with Alfven waves. At the proton gyroscale, they are longest along the local mean field direction and shortest in the direction perpendicular to the local mean field and the local field fluctuation. The compressive fluctuations are highly elongated along the local mean field direction, although axially symmetric perpendicular to it. Their large anisotropy may explain why they are not heavily damped in the solar wind.