Propagation velocities and dimensions of plasmoid structures in the near-Earth magnetotail

Measurements from the High Energy Particle - Low energy particle Detector e xperiment (HEP-LD) and Magnetic Field experiment (MGF) onboard the GEOTAIL spacecraft are used to estimate characteristic flow velocities and scale si zes of plasmoid structures released in the near-Earth magnetotail during su bstorm events. Bulk velocities are derived from the azimuthal distribution of energetic ions and typical scale sizes are thereafter calculated from th e duration of the plasmoid signatures. The results show great variability f rom one event to another. Velocities range from 250 - 700 km/s and scale si zes were in the range 3 - 9 R-E for the events studied. Despite the great v ariability, the velocities are somewhat lower than earlier observations fro m the distant tail.