Direct observations of passages of the distant neutral line (80‐140 RE) following substorm pnsets: ISEE‐3

Detailed plasma and field data are examined for a period of time when ISEE‐3 is in the range −140 ≲ XGSM ≲ −80 RE. Several clear examples, at a frequency of ∼ once per day, of strong southward magnetic field followed by strong northward field occur when ISEE‐3 is in the plasma sheet. During the southward field intervals, the bulk plasma flow is strongly tailward while during the northward field episodes the plasma flow is generally very weak. In all instances of this kind, the signatures at ISEE‐3 follow (by 5‐10 minutes) the initial impulsive injection of energetic ions at geostationary orbit. It is suggested that the south‐to‐north field transitions and plasma flow patterns are produced by the passage over ISEE‐3 of the distant neutral line immediately following near‐earth substorm onset.