Effects of Solar Activity on Taylor Scale and Correlation Scale in Solar Wind Magnetic Fluctuations

TL;DR

This study investigates how solar activity influences the turbulence scales in solar wind magnetic fluctuations, revealing a strong positive correlation between sunspot number and the Taylor scale, challenging traditional turbulence theories.

Contribution

It provides the first comprehensive analysis linking solar activity to turbulence scales in solar wind, highlighting limitations of hydrodynamic theories at kinetic dissipation scales.

Findings

Taylor scale increases with sunspot number

Correlation coefficient between sunspot number and Taylor scale is 0.92

Hydrodynamic turbulence theory is incomplete for solar wind

Abstract

The correlation scale and the Taylor scale are evaluated for interplanetary magnetic field fluctuations from two-point, single time correlation function using the Advanced Composition Explorer (ACE), Wind, and Cluster spacecraft data during the time period from 2001 to 2017, which covers over an entire solar cycle. The correlation scale and the Taylor scale are respectively compared with the sunspot number to investigate the effects of solar activity on the structure of the plasma turbulence. Our studies show that the Taylor scale increases with the increasing sunspot number, which indicates that the Taylor scale is positively correlated with the energy cascade rate, and the correlation coefficient between the sunspot number and the Taylor scale is 0.92. However, these results are not consistent with the traditional knowledge in hydrodynamic dissipation theories. One possible explanation is that in the solar wind, the fluid approximation fails at the spatial scales near the dissipation ranges. Therefore, the traditional hydrodynamic turbulence theory is incomplete for describing the physical nature of the solar wind turbulence, especially at the spatial scales near the kinetic dissipation scales.