Tracking a major interplanetary disturbance with SMEI

Abstract

We present the first clear observations of an Earth‐directed interplanetary disturbance tracked by the Solar Mass Ejection Imager (SMEI). We find that this event can be related to two halo CMEs seen at the Sun about 2 days earlier, and which merged in transit to 1 AU. The disturbance was seen about 16 hours before it reached Earth,and caused a severe geomagnetic storm at the time which would have been predicted had SMEI been operating as a real‐time monitor. It is concluded that SMEI is capable of giving many hours advance warning of the possible arrival of interplanetary disturbances.