Self-Similarity of ICME Flux Ropes: Observations by Radially Aligned Spacecraft in the Inner Heliosphere

TL;DR

This study investigates the magnetic flux ropes within ICMEs observed by radially aligned spacecraft, revealing strong structural similarities and insights into their evolution during propagation in the inner heliosphere.

Contribution

It introduces a simple mapping technique to compare flux rope structures across spacecraft and applies Lundquist fitting to analyze flux rope orientations and their evolution.

Findings

Strong structural similarities in flux ropes across spacecraft

Mapping technique uncovers hidden similarities in magnetic profiles

Flux rope axes tend to align with the solar east-west direction with distance

Abstract

Interplanetary coronal mass ejections (ICMEs) are a significant feature of the heliospheric environment and the primary cause of adverse space weather at the Earth. ICME propagation, and the evolution of ICME magnetic field structure during propagation, are still not fully understood. We analyze the magnetic field structures of 18 ICME magnetic flux ropes observed by radially aligned spacecraft in the inner heliosphere. Similarity in the underlying flux rope structures is determined through the application of a simple technique that maps the magnetic field profile from one spacecraft to the other. In many cases, the flux ropes show very strong underlying similarities at the different spacecraft. The mapping technique reveals similarities that are not readily apparent in the unmapped data and is a useful tool when determining whether magnetic field time series observed at different spacecraft are associated with the same ICME. Lundquist fitting has been applied to the flux ropes and the rope orientations have been determined; macroscale differences in the profiles at the aligned spacecraft may be ascribed to differences in flux rope orientation. Assuming that the same region of the ICME was observed by the aligned spacecraft in each case, the fitting indicates some weak tendency for the rope axes to reduce in inclination relative to the solar equatorial plane and to align with the solar east-west direction with heliocentric distance.