Observational evidence for self-generation of small-scale magnetic flux ropes from intermittent solar wind turbulence

TL;DR

This study provides observational evidence that small-scale magnetic flux ropes in the solar wind are self-generated by turbulence, with a comprehensive 20-year database showing their distribution and properties.

Contribution

It introduces a large-scale observational database and analysis confirming the self-generation mechanism of flux ropes from solar wind turbulence.

Findings

Flux ropes occur about 3,500 times per year with solar cycle dependence.

The wall-to-wall time distribution follows a power-law consistent with turbulence.

Axial current density distribution is non-Gaussian, matching simulation results.

Abstract

We present unique {and additional} observational evidence for the self-generation of small-scale coherent magnetic flux rope structures in the solar wind. Such structures with durations between 9 and 361 minutes are identified from Wind in-situ spacecraft measurements through the Grad-Shafranov (GS) reconstruction approach. The event occurrence counts are on the order of 3,500 per year on average and have a clear solar cycle dependence. We build a database of small-scale magnetic flux ropes from twenty-year worth of Wind spacecraft data. We show a power-law distribution of the wall-to-wall time corresponding well to the inertial range turbulence, which agrees with relevant observations and numerical simulation results. We also provide the axial current density distribution from the GS-based observational analysis, which yields a non-Gaussian probability density function consistent with numerical simulation results.