Can Alfv\'enic Fluctuations Affect the Correlation and Complexity of Magnetic Fields in Magnetic Ejecta? A Case Study Based on Multi-Spacecraft Measurements at 1~au

TL;DR

This study examines how Alfvénic fluctuations influence the magnetic structure and complexity of magnetic ejecta in interplanetary coronal mass ejections, using multi-spacecraft measurements at 1 au to analyze correlations and fluctuations.

Contribution

It provides the first detailed analysis of the impact of Alfvénic fluctuations on magnetic ejecta structure using simultaneous multi-spacecraft observations at 1 au.

Findings

AFs occur in the rear region of the ME with about six-hour duration.

AFs are associated with decreased magnetic field correlation between spacecraft.

AFs increase the magnetic complexity detected at different spacecraft.

Abstract

We investigate whether Alfv\'enic fluctuations (AFs) can affect the structure of magnetic ejecta (MEs) within interplanetary coronal mass ejections (ICMEs). We study an ICME observed on 2001 December 29 at 1 au by ACE and Wind, at a total angular separation of $\sim$0.8$^\circ$ ($\sim0.014$~au). We focus on the correlation and complexity of its magnetic structure measured between two spacecraft in association with large-amplitude AFs. The Alfv\'enicity of the ME is investigated in terms of the residual energy and cross helicity of fluctuations. We find that as for the event of interest, large-amplitude AFs occur in the rear region of the ME at both Wind and ACE with a duration of about six hours. We compare the correlation of the magnetic field strength and vector components measured between Wind and ACE, and investigate complexity in terms of the magnetic hodograms. The region showing AFs is found to be associated with a decreased correlation of the magnetic field components and an increased complexity of the ME magnetic configuration detected at ACE and Wind, which may be due to the fact that the two spacecraft crossing the same ME along different trajectories likely sampled AFs in different oscillation phases. Combining multi-point in-situ measurements and remote-sensing observations of the ICME source region, we further discuss different potential sources of the AFs.