Self-similar expansion of solar coronal mass ejections: implications for Lorentz self-force driving

TL;DR

This study analyzes the self-similar expansion of solar coronal mass ejections (CMEs) and suggests that Lorentz self-forces drive their propagation, based on observations of flux rope structures and their magnetic configurations.

Contribution

It demonstrates that CMEs expand self-similarly and provides evidence that Lorentz self-forces, rather than force-free magnetic fields, drive their propagation.

Findings

CMEs exhibit approximately self-similar expansion.

Magnetic and current configurations deviate from force-free states.

Lorentz self-forces are validated as the driving mechanism.

Abstract

We examine the propagation of several CMEs with well-observed flux rope signatures in the field of view of the SECCHI coronagraphs aboard the STEREO satellites using the GCS fitting method of Thernisien, Vourlidas \& Howard (2009). We find that the manner in which they propagate is approximately self-similar; i.e., the ratio ($\kappa$) of the flux rope minor radius to its major radius remains approximately constant with time. We use this observation of self-similarity to draw conclusions regarding the local pitch angle ($\gamma$) of the flux rope magnetic field and the misalignment angle ($\chi$) between the current density ${\mathbf J}$ and the magnetic field ${\mathbf B}$. Our results suggest that the magnetic field and current configurations inside flux ropes deviate substantially from a force-free state in typical coronagraph fields of view, validating the idea of CMEs being driven by Lorentz self-forces.