Large Geomagnetic Storms Associated with Limb Halo Coronal Mass Ejections

TL;DR

This study analyzes limb halo coronal mass ejections during solar cycle 23, confirming that geomagnetic storms from these events are primarily caused by the sheath regions of interplanetary CMEs, with some storms linked to other sources.

Contribution

It provides detailed evidence that sheath regions of limb halo CMEs are the main drivers of associated geomagnetic storms, clarifying the role of different CME components.

Findings

Sheath regions of limb halo CMEs cause most associated geomagnetic storms.

Some storms attributed to limb halos are actually caused by other disk halos.

Interaction events between limb halos can influence storm causation.

Abstract

Solar cycle 23 witnessed the observation of hundreds of halo coronal mass ejections (CMEs), thanks to the high dynamic range and extended field of view of the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) mission. More than two thirds of halo CMEs originating on the front side of the Sun have been found to be geoeffective (Dst =< -50 nT). The delay time between the onset of halo CMEs and the peak of ensuing geomagnetic storms has been found to depend on the solar source location (Gopalswamy et al., 2007). In particular, limb halo CMEs (source longitude > 45deg) have a 20% shorter delay time on the average. It was suggested that the geomagnetic storms due to limb halos must be due to the sheath portion of the interplanetary CMEs (ICMEs) so that the shorter delay time can be accounted for. We confirm this suggestion by examining the sheath and ejecta portions of ICMEs from Wind and ACE data that correspond to the limb halos. Detailed examination showed that three pairs of limb halos were interacting events. Geomagnetic storms following five limb halos were actually produced by other disk halos. The storms followed by four isolated limb halos and the ones associated with interacting limb halos, were all due to the sheath portions of ICMEs.