Characteristic Scales of Complexity and Coherence within Interplanetary Coronal Mass Ejections: Insights from Spacecraft Swarms in Global Heliospheric Simulations

TL;DR

This study uses large-scale simulations with spacecraft swarms to analyze the magnetic complexity and coherence scales of interplanetary coronal mass ejections, revealing how interactions and geometry influence their structure and evolution.

Contribution

It introduces a novel simulation approach with extensive spacecraft swarms to quantify ICME magnetic coherence and complexity, informing future multi-spacecraft mission planning.

Findings

ICMEs have higher coherence along their magnetic axis.

Global complexity characterization requires multiple spacecraft crossings.

Interactions with solar wind structures significantly reduce coherence.

Abstract

Many aspects of the three-dimensional (3-D) structure and evolution of interplanetary coronal mass ejections (ICMEs) remain unexplained. Here, we investigate two main topics: (1) the coherence scale of magnetic fields inside ICMEs, and (2) the dynamic nature of ICME magnetic complexity. We simulate ICMEs interacting with different solar winds using the linear force-free spheromak model incorporated into the EUHFORIA model. We place a swarm of ~20000 spacecraft in the 3-D simulation domain and characterize ICME magnetic complexity and coherence at each spacecraft based on simulated time series. Our simulations suggest that ICMEs retain a lower complexity and higher coherence along their magnetic axis, but that a characterization of their global complexity requires crossings along both the axial and perpendicular directions. For an ICME of initial half angular width of $45^\circ$ that does not interact with other large-scale solar wind structures, global complexity can be characterized by as little as 7-12 spacecraft separated by $25^\circ$, but the minimum number of spacecraft rises to 50-65 (separated by $10^\circ$) if interactions occur. Without interactions, ICME coherence extends for $45^\circ$, $20^\circ$-$30^\circ$, $15^\circ$-$30^\circ$, and $0^\circ$-$10^\circ$ for $B$, $B_\phi$, $B_\theta$, and $B_r$, respectively. Coherence is also lower in the ICME west flank compared to the east flank due to Parker spiral effects. Moreover, coherence is reduced by a factor of 3-6 by interactions with solar wind structures. Our findings help constrain some of the critical scales that control the evolution of ICMEs and aid in the planning of future dedicated multi-spacecraft missions.