A POSSIBLE CASE OF RADIALLY ANTISUNWARD PROPAGATING SUBSTORM ONSET IN THE NEAR-EARTH MAGNETOTAIL

It is generally thought that the local effects associated with substorm onset in the near-Earth magnetotail (R ≲ 10RE) have a component of propagation which is radially earthward. This study presents a case during which it is possible that the local effects of substorm onset propagated radially antisunward. We examine energetic ion and magnetic field data from AMPTE/CCE and energetic particle data from the geosynchronous satellite 1982-019 during a period of weak substorm activity on 11 June 1985. Although the effects of this event on the ground were very weak, the substorm had a dramatic effect on at least one portion of the near-Earth magnetotail. During the period of interest the spacecraft were in an unusually close radial alignment. The data show that phenomena which we associate with the local effects of substorm onset began at or near geosynchronous before they were observed at CCE (R = 8.8RE). We believe that this event is best explained by a near-Earth disruption of the cross-tail current sheet and the consequent formation of a substorm current wedge, and that this process had a component of expansion antisunward down the tail. © 1990.