Halo Coronal Mass Ejections and Configuration of the Ambient Magnetic Fields

In this study, we seek a correlation between the speed of active region-related halo coronal mass ejections (CMEs) and the configuration of the ambient magnetic fields. Having studied 99 halo CMEs in the period from 2000 to 2004, we find that CMEs under the heliospheric current sheet are significantly slower than CMEs situated under unidirectional open field structures. The average speed of the former is 883 km s-1, while the latter is 1388 km s-1. The effect is not biased by the flare importance. This implies that the ambient magnetic field structure plays a role in determining the speed of the halo CMEs.