Erosion and the Dynamic Development of Dayside Plasmaspheric Drainage Plumes, as Seen by IMAGE EUV J. Goldstein, M. Spasojevic, B. R. Sandel, S. Sazykin, R. A. Wolf, R. W. Spiro, and P. H. Reiff The plasmapause is the outer boundary of the Earth's plasmasphere. Even after decades of in situ and ground-based whistler observations, the details of the erosion process remain unknown, although it is generally understood that both the co-rotation and convection electric fields play a role. The IMAGE satellite's extreme ultraviolet (EUV) imager, which routinely obtains full global images of the plasmasphere as seen in 30.4 nm light, directly observes the effects of plasmaspheric erosion by capturing the motion of the plasmapause, and a handful of erosion events have been examined. For a larger number of events, the plasmapause motion associated with erosion was not directly captured because the erosion occurred during gaps in EUV data coverage; however, observation of reduced plasmapause radial location on successive EUV passes provides indirect evidence of erosion. From the EUV erosion events identified thus far, the following global erosion process has been deduced. Erosion triggers a "sunward surge" of plasma that produces outward motion of the plasmapause on the dayside. As part of the erosion process, a "plume" of plasmaspheric material is formed. At the start of a major erosion event, this plume is quite broad in local time, often filling the entire dayside with "eroded'" plasmaspheric plasma that is participating in the sunward surge. As the erosion proceeds, the local-time extent of the dayside plume narrows as the western edge of the plume migrates eastward while the eastern edge of the plume remains roughly stationary in local time. We shall present this erosion and plume formation picture from an observational and theoretical/simulational perspective. _______________ Presented at the Magnetospheric Imaging Workshop, Yosemite National Park, California, U.S.A., Feb. 9 - 13, 2003.