Case Study of Two Neighbouring Interplanetary Coronal Mass Ejections

Wai Leong Teh

Abstract


Two neighbouring interplanetary coronal mass ejections (ICMEs; ICME1 and ICME2) at 1 AU, separated by ~33 hours, were compared in terms of sheath properties, geoeffectiveness, and two-dimensional (2-D) geometry. These two ICMEs have a bipolar pattern in the north-south field component. ICME2 moved at a speed of ~521 km/s, faster than the preceding ICME1 at ~460 km/s. Planar magnetic structures were found in the sheath of both ICMEs. The geomagnetic index SYM-H reached a minimum at -36 nT and -86 nT for ICME1 and ICME2, respectively. More moderate geomagnetic disturbances were caused by ICME2, due to a larger southward magnetic field. The 2-D magnetic field maps, produced by the Grad-Shafranov reconstruction, show that the two ICMEs resemble a magnetic flux rope structure but their axial directions are oppositely oriented. When viewed from the Earth, ICME1 is a right-handedness flux rope while ICME2 is a left-handedness one. This result suggests that these two ICMEs are not part of one another.


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