CROSS-TAIL MAGNETIC-FLUX ROPES AS OBSERVED BY THE GEOTAIL SPACECRAFT

Ten transient magnetic structures in Earth's magnetotail, as observed in GEOTAIL measurements, selected for early 1993 [at (-) X(GSM) = 90 - 130 R(E)], are shown to have helical magnetic field configurations similar to those of interplanetary magnetic clouds at 1 AU but smaller in size by a factor of approximate to 700. Such structures are shown to be well approximated by a comprehensive magnetic force-free flux-rope model. For this limited set of 10 events the rope axes are seen to be typically aligned with the Y-GSM axis and the average diameter of these structures is approximate to 15 RE.