Ruhr University, Bochum, Federal Republic of Germany

Statistical studies of the ISEE 3 deep magnetic tail data (r ³ 120 R_E) show that the bulk electron plasma flow is virtually always tailward during both quiet and geomagnetically active times. This aspect of the magnetotail data has been interpreted as suggesting that ISEE 3 is nearly always tailward of the distant neutral line when the spacecraft is at distances ³ 120 R_E. During an extended period (~ 0900 to ~ 1230 UT) on January 29, 1983, however, ISEE 3 observed substantial earthward plasma flows while located in the distant plasma sheet at X_GSM = -217 R_E. We have analyzed the distant neutral line location within the context of the distant tail, geostationary orbit, auroral zone, and solar wind data for this case based on an extension of the Coroniti and Kennel (1972) flaring tail theory. We conclude from known solar wind conditions that for a typical neutral line location at ~ 135 R_E, an ~ 30% increase of the near-Earth lobe field strength would be required to cause the distant neutral line to move tailward beyond 220 R_E. The available data suggest that this is quite plausible and that, therefore, the earthward flow episode is due to an exceptionally distant neutral line position. The question of why substorms did not terminate the growth phases earlier is also addressed.

J. Geophys. Res., 94, No. A11, 15177-15188, 1989