Enhancements of lobe ion density and velocity associated with plasmoids

Intermittent enhancements of lobe ions in density and velocity were observed by the GEOTAIL spacecraft in the distant magnetotail (similar to100-200 R-E). They were observed after the passage of plasmoids, accompanying south-to-north bipolar variations in Bz, which axe opposite in polarity to those observed with plasmoids or traveling compression regions. The peaks in the ion density occurred when Bz changed from south to north (i.e., when Bz = 0). To explain these observations, a model is presented in which the magnetotail shrinks behind a plasmoid. It is suggested that after the formation of a plasmoid the near-Earth neutral line runs tailward following the plasmoid. The delay between the plasmoid passage and the ion enhancement observed by the same spacecraft is similar to5-70 min, depending on as yet unknown reasons.