Deflection of Coronal Mass Ejections in Unipolar Ambient Magnetic Fields

TL;DR

This study uses magnetohydrodynamic simulations to show that coronal mass ejections can significantly deviate from radial paths in unipolar magnetic fields due to an effective I×B force, impacting space weather predictions.

Contribution

It introduces a new mechanism for CME deflection in unipolar fields, independent of ambient field asymmetry, enhancing understanding of CME trajectories.

Findings

CME trajectories deviate significantly below ~15 solar radii.

The deviation is caused by an effective I×B force from flux rope currents.

Results improve predictions of CME paths for space weather forecasting.

Abstract

The trajectories of coronal mass ejections (CMEs) are often seen to substantially deviate from a purely radial propagation direction. Such deviations occur predominantly in the corona and have been attributed to "channeling" or deflection of the eruptive flux by asymmetric ambient magnetic fields. Here, we investigate an additional mechanism that does not require any asymmetry of the pre-eruptive ambient field. Using magnetohydrodynamic numerical simulations, we show that the trajectory of CMEs through the solar corona can significantly deviate from a radial direction when propagation takes place in a unipolar radial field. We demonstrate that the deviation is most prominent below ~15 solar radii and can be attributed to an "effective IxB force" that arises from the intrusion of a magnetic flux rope with a net axial electric current into a unipolar background field. These results are important for predictions of CME trajectories in the context of space weather forecasts, as well as for reaching a deeper understanding of the fundamental physics underlying CME interactions with the ambient fields in the extended solar corona.