Structure of plasmaspheric plumes and their participation in magnetopause reconnection: First results from THEMIS

New observations by the THEMIS spacecraft have revealed dense (> 10 cm(-3)) plasmaspheric plumes extending to the magnetopause. The large scale radial structure of these plumes is revealed by multi- spacecraft measurements. Temporal variations in the radial distribution of plume plasma, caused by azimuthal density gradients coupled with azimuthal flow, are also shown to contribute to plume structure. In addition, flux tubes with cold plume plasma are shown to participate in reconnection, with simultaneous observations of cold ions and reconnection flow jets on open flux tubes as revealed by the loss of hot magnetospheric electrons.