Plots of plasmaspheric ion (right) and electron (below) density show significant density structure in the plasma trough region outside the plasmapause. In both panels, the y axis gives the particle density, while the x axis indicates the position in L. The top panel shows a well-defined plasmapause at L ~ 4.2, with structure extending out to the magnetopause. In the bottom panel, high density structures can be seen at L ~ 5.5-6 and from L = 7-9. The structuring in the middle and outer magnetosphere evident in these data indicates the presence of dense plasma regions beyond the plasmapause. These regions consist of material that has been eroded from the plasmasphere by enhanced convection and that may be in the form either of detached plasma patches or of plasma plumes or tails extending from the main body of the plasmasphere. The data in the top panel were acquired with the ion mass spectrometer on the Ogo 5 spacecraft; those in the bottom panel, with the sweep frequency receiver on the ISEE 1 satellite. As indicated by the trajectory plot in the upper righthand corner of the bottom panel, the ISEE measurements were made in the afternoon-evening sector of the magnetosphere; the Ogo data were taken in the morning-noon sector.