Solar Filaments and Interplanetary Magnetic Field Bz

The direction of the axis of an interplanetary coronal mass ejection (ICME) plays an important role in determining if it will cause a geomagnetic disturbance in the Earth's magnetosphere upon impact. Long period southward-pointing ICME fields are known to cause significant space weather impacts and thus geomagnetic storms. We present an extensive analysis of CME-ICME directionality using 86 halo-CMEs observed between 2007 and 2017 to compare the direction of the source filament axial magnetic field on the Sun and the direction of the interplanetary magnetic field near the Earth at the L1 Lagrangian point. Excluding 12 cases that were too ambiguous to determine, for the remaining 74 ICMEs, we find an agreement in terms of the northward/southward orientation of Bz between ICMEs and their CME source regions in 85% of cases. Some of the previous studies discussed here have obtained an agreement of 77% and 55%. We therefore suggest that our method can be meaningful as a first step in efficiently predicting geoeffective ICMEs by observing and analyzing the source regions of CMEs on the Sun.