A distinctive characteristic of interplanetary magnetic clouds is their rope-like magnetic structure, i.e., their smoothly-varying helical field lines whose pitch increases from their core to their boundary. Because this regular structure helps to make MCs particularly geo-effective, it is important to understand how it arises.

We discuss recent work which relates the magnetic and topological parameters of MCs to associated solar active regions. This work strongly supports the notion that MCs associated with active region eruptions are formed by magnetic reconnection between these regions and their larger-scale surroundings, rather than simple eruption or entrainment of pre-existing structures in the corona or chromosphere. We discuss our findings in the context of other recent works on both the solar and interplanetary sides, including ion composition and various MHD models of magnetic cloud formation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html