Correlation functions of small-scale fluctuations of the interplanetary magnetic field

TL;DR

This study uses multi-point Cluster spacecraft data to analyze the three-dimensional correlation functions of small-scale magnetic field fluctuations in the solar wind, revealing anisotropy and variable correlation lengths.

Contribution

It provides the first detailed three-dimensional correlation functions of interplanetary magnetic field fluctuations from multi-spacecraft data, enhancing understanding of solar wind turbulence.

Findings

Correlation length varies over six orders of magnitude.

Turbulence exhibits significant anisotropy with two distinct populations.

Correlation ellipsoids show preferred orientations and high anisotropy in certain intervals.

Abstract

The Interplanetary Magnetic Field shows complex spatial and temporal variations. Single spacecraft measurements reveal only a one dimensional section of this rich four dimensional phenomenon. Multi-point measurements of the four Cluster spacecraft provide a unique tool to study the spatiotemporal structure of the field. Using Cluster data we determined three dimensional correlation functions of the fluctuations. By means of the correlation function one can describe and measure field variations. Our results can be used to verify theoretical predictions, to understand the formation and nature of solar wind turbulence. We found that the correlation length varies over almost six orders of magnitude. The IMF turbulence shows significant anisotropy with two distinct populations. In certain time intervals the ratio of the three axes of the correlation ellipse is 1/2.2/6 while in the remaining time we found extremely high correlation along one axis. We found favoured directions in the orientation of the correlation ellipsoids.