Successive interacting coronal mass ejections: Preconditioning, magnetic reconnection and flux erosion: How to create a perfect storm?

Coronal mass ejections (CMEs) are the largest type of eruption seen on our Sun and the primary cause of geomagnetic disturbances and storms when they arrive at the Earth. Most geomagnetic storms are created by the impact of single CME yet in a significant fraction of cases they are caused by the interaction of multiple CMEs or CMEs with other transient phenomena. In this paper we implement a spheromak CME description within our 3-D heliospheric MHD model and self-consistently model their interactions with the pre-existing solar wind and with one another. We assess their geo-effectiveness at 1 AU through quantification of the relevant solar wind variables and an empirical measures based upon solar wind-magnetosphere coupling functions. We show how the orientation and handedness of a given CME can have a significant impact on its geoeffectivness due to a prolonged conservation of toroidal flux caused by differential interplay with the Parker Spiral, and how a large range of possible CME-CME interactions can produce a diverse range of geophysical impacts at the Earth.