Average flow between ∼70 RE and ∼220 RE in the geomagnetic tail

The ISEE‐3 spacecraft was transferred in 1982 into the magnetotail, where it was kept for about 1 year via succesive lunar swingbys. The Max‐Planck‐Institut/University of Maryland sensor on ISEE‐3 provides energetic ion measurements above ∼30 keV/charge. Assuming that the energetic protons are convected with the local plasma flow we are able to determine the convection velocity from the measured angular distributions and the differential spectrum. A statistical analysis of the flow magnitude and direction at various distance ranges reveals the following: The average tailward flow velocity between 203 and 220 R E is 567 km/s and earthward flow occurs in less than 1% of all cases. At a radial distance of 117 to 153 R E the result is similar; the average tailward flow velocity is found to be 665 km/s and earthward flow occurs in less than 6% of all measurements. This is in contrast to findings at radial distances of 61 to 76 R E . Here, equal probability for earthward and tailward flow has been found and average flow velocities are 336 km/s in both directions. These results indicate that magnetic neutral lines rarely move or form beyond ∼100 R E .