Solar and interplanetary triggers of the largest Dst variations of the solar cycle 23

We present the results of an investigation from the Sun to the Earth of the sequence of events that caused major Dst decreases (ΔDst≤-100 nT during 1 h) that occurred during 1996-2005. These events are expected to be better related to geomagnetic induced current (GIC) events than those events where any geomagnetic index is far from its quiet time value. At least one full halo CME with a speed on the plane of sky above 900 km/s participates in every studied event. The seven events were triggered by interplanetary signatures, which arise as a consequence of interaction among different solar ejections. The interaction arises at different stages from the solar surface, between segments of a filament, to the interplanetary medium, appearing as ejecta or multiple-magnetic clouds (MultiMCs). In other cases, shock waves overtake or compress previous ICMEs and at other times the interaction also appears between magnetic clouds (MCs) and streams.