A New Class of Complex Ejecta Resulting from the Interaction of two CMEs   and its Expected Geoeffectiveness
  A significant portion of transients measured by spacecraft at 1 AU does not show the well-defined properties of magnetic clouds (MCs). Here, we propose a new class of complex, non-MC ejecta resulting from the interaction of two CMEs with different orientation, which differ from the previously studied multiple-MC event. At 1 AU, they are associated with a smooth rotation of the magnetic field vector over an extended duration and do not show clear signs of interaction. We determine the characteristics of such events based on a numerical simulation and identify and analyze a potential case in the long-duration CME measured in situ in 2001 March 19-22. Such events may result in intense, long-duration geo-magnetic storms, with sawtooth events, and may sometimes be misidentified as isolated CMEs. 
N. Lugaz and C. J. Farrugia
astro-ph.SR physics.space-ph