J. A. Slavin, M. Hesse, C. J. Owen, S. Taguchi, D. H. Fairfield, R. P. Lepping, S. Kokubun, T. Mukai, A. T. Y. Lui, R. R. Anderson, H. Matsumoto, P. R. Sutcliffe

Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771

This study examines a data set returned by IMP 8 and Geotail on January 29, 1995, during a substorm which resulted in the ejection of a plasmoid. The two spacecraft (s/c) were situated in the north lobe of the tail and both observed a traveling compression region (TCR). We show that in this instance dual s/c measurements can be used to model all three dimensions of the underlying plasmoid and to estimate its rate of expansion. For this event plasmoid dimensions of D X ~ 18, D Y ~ 30, and D Z ~ 10 R_e are determined from the IMP 8 and Geotail observations. Furthermore, a factor of ~ 2 increase in the amplitude of the TCR occurred in the 1.5 min it took to move from IMP 8 to Geotail. Modeled using conservation implies that the underlying plasmoid was expanding at a rate of ~ 140 km/s. Finally, a reconfiguration of the lobe magnetic field followed plasmoid ejection which moved magnetic flux tubes into the wake behind the plasmoid where they would become available to feed the reconnection region.

Geophys. Res. Lett., 26, No. 19, 2897-2900, Oct. 1999