Successive CMEs and complex ejecta

We identified three sets of successive halo CMEs directed toward Earth (two or more CMEs observed within 1–4 days in the corona) and the corresponding flows and magnetic fields at 1 AU. Each set of successive halo CMEs was associated with complex ejecta at 1 AU. Complex ejecta were defined by Burlaga et al. [2001] as fast (>600 km/s) flows that are neither corotating flows nor magnetic clouds, which move past Earth during a day or more. They correspond to the transient flows discussed in the literature prior to the discovery of magnetic clouds. We infer that in each case the successive CMEs merged en route from the Sun to the Earth to form complex ejecta. In general, the components of the complex ejecta corresponding to individual CMEs cannot be identified, suggesting that the merging process is nonlinear and irreversible, and memory of the conditions near the sun is lost in the process. The identity of the individual CMEs is gradually lost as the interaction proceeds within 1 AU. In some cases, the interaction can result in what appears to be a single stream in the speed profile at 1 AU. Nevertheless, given observations of successive halo CMEs, one can possibly predict the arrival of complex ejecta or more complicated transient flow systems at 1 AU. In some cases, complex ejecta related to multiple CMEs can be associated with a single source region, an active region.