The Nature of Subproton Scale Turbulence in the Solar Wind

TL;DR

This paper investigates the nature of subproton scale turbulence in the solar wind, providing observational, analytical, and numerical evidence that kinetic Alfven turbulence dominates over whistler turbulence at these scales.

Contribution

It offers the first comprehensive evidence that kinetic Alfven turbulence is the primary form of subproton scale fluctuations in the solar wind.

Findings

Kinetic Alfven turbulence dominates subproton scales.

Whistler turbulence, if present, is a minor component.

New observational data supports the dominance of kinetic Alfven turbulence.

Abstract

The nature of subproton scale fluctuations in the solar wind is an open question, partly because two similar types of electromagnetic turbulence can occur: kinetic Alfven turbulence and whistler turbulence. These two possibilities, however, have one key qualitative difference: whistler turbulence, unlike kinetic Alfven turbulence, has negligible power in density fluctuations. In this Letter, we present new observational data, as well as analytical and numerical results, to investigate this difference. The results show, for the first time, that the fluctuations well below the proton scale are predominantly kinetic Alfven turbulence, and, if present at all, the whistler fluctuations make up only a small fraction of the total energy.