Relationship between earth-directed solar eruptions and magnetic clouds at 1AU: A brief review

TL;DR

This review examines the relationship between solar eruptions, magnetic clouds, and their magnetic field orientations, highlighting that halo CME elongation generally reflects the underlying flux rope orientation and that the neutral line tilt correlates with magnetic cloud axes.

Contribution

It provides a comprehensive analysis of 100 events showing that CME elongation and magnetic cloud orientation are reliably related, emphasizing the influence of heliospheric magnetic fields on ejecta.

Findings

Most halo CMEs are elongated along the flux rope axis.

The neutral line tilt correlates with magnetic cloud axes.

Projection effects do not significantly distort CME appearance.

Abstract

We review relationships between coronal mass ejections (CMEs), EIT post eruption arcades, and the coronal neutral line associated with global magnetic field and magnetic clouds near the Earth. Our previous findings indicate that the orientation of a halo CME elongation may correspond to the orientation of the underlyig flux rope. Here we revisit these preliminary reports by comparing orientation angles of elongated LASCO CMEs, both full and partial halos, to the post eruption arcades. Based on 100 analysed events, it was found that the overwhelming majority of halo CMEs are elongated in the direction of the axial field of the post eruptio arcades. Moreover, this conclusion also holds for partial halo CMEs as well as for events that originate further from the disk center. This suggests that the projection effect does not drastically change the appearance of full and partial halos and their imagesstill bear reliable information about the underlying magnetic fields. We also compared orientations of the erupted fields near the Sun and in the interplanetary space and found that the local tiltof the coronal neutral line at 2.5 solar radii is well correlated with the magnetic cloud axis measured near the Earth. We suggest that the heliospheric magnetic fields significantly affect the propagating ejecta. Sometimes, the ejecta may even rotate so that its axis locally aligns itself with the heliospheric current sheet.