Magnetic Field Rotations in the Solar Wind at Kinetic Scales

TL;DR

This study extends analysis of magnetic field rotations in the solar wind from MHD to kinetic scales, revealing how rotation angles and energy distribution change at smaller scales, impacting turbulence dissipation understanding.

Contribution

It provides the first detailed statistical characterization of magnetic field rotations at ion and electron kinetic scales in the solar wind.

Findings

Rotation angles follow a log-normal distribution that shifts to smaller angles at smaller scales.

Energy in fluctuations decreases exponentially with increasing rotation angle.

Large rotation angles contain negligible energy at kinetic scales.

Abstract

The solar wind magnetic field contains rotations at a broad range of scales, which have been extensively studied in the MHD range. Here we present an extension of this analysis to the range between ion and electron kinetic scales. The distribution of rotation angles was found to be approximately log-normal, shifting to smaller angles at smaller scales almost self-similarly, but with small, statistically significant changes of shape. The fraction of energy in fluctuations with angles larger than $\alpha$ was found to drop approximately exponentially with $\alpha$, with e-folding angle $9.8^\circ$ at ion scales and $0.66^\circ$ at electron scales, showing that large angles ($\alpha > 30^\circ$) do not contain a significant amount of energy at kinetic scales. Implications for kinetic turbulence theory and the dissipation of solar wind turbulence are discussed.