Solar cycle dependence of spatial correlation in the solar wind

TL;DR

This study examines how the spatial correlation lengths of solar wind fluctuations vary with the solar cycle, revealing cycle-dependent differences in density and magnetic field magnitude correlations using spacecraft data.

Contribution

It introduces a nonlinear mutual information approach to analyze solar wind correlations and highlights the solar cycle dependence of correlation lengthscales for different parameters.

Findings

Correlation length of |B| varies from ~120 Re at solar minimum to ~270 Re at maximum.

Density correlation length increases from ~75 Re at minimum to ~170 Re at maximum.

Magnetic field component correlations do not significantly vary with the solar cycle.

Abstract

We investigate the spatial correlation properties of the solar wind using simultaneous observations by the ACE and WIND spacecraft. We use mutual information as a nonlinear measure of correlation and compare this to linear correlation. We find that the correlation lengthscales of fluctuations in density and magnetic field magnitude vary strongly with the solar cycle, whereas correlation lengths of fluctuations in B field components do not. We find the correlation length of |B| ~ 120 Re at solar minimum and ~ 270 Re at maximum and the correlation length of density ~ 75 Re at minimum and ~ 170 Re at minimum. The components of the B field have correlation lengths ~ correlation length |B| at minimum.