ISEE 3 magnetic field observations in the magnetotail Implications for reconnection

Early results are presented from an analysis of magnetometer measurements made during the first two tail passes of ISEE-3. ISEE-3 explored the magnetotail to a distance of 220 earth radii during its first two tail orbits. The field strength in the lobes and the Bz component in the plasma sheet decreased systematically with distance. The frequency of occurrence of negative Bz increased with distance. The observations suggest the existence of an x-type neutral line located on average near 200 earth radii. In addition to the systematic variations with distance, three types of transient events were recorded. The first (encountered on more than 30 occasions) is a discrete magnetic structure which Hones has identified as tailward moving plasmoids produced by reconnection within the tail. The second type of event seems to be a peripheral encounter with the plasmoids making up the first type. The third type, unlike the y-aligned plasmoids, have x-aligned axes; they have the characteristics of magnetic flux ropes lying parallel to the tail. 11 references