The radial and longitudinal propagation characteristics of substorm injections

Abstract

In this paper we present a statistical study of the radial and azimuthal propagation of substorm effects in the near-geosynchronous magnetotail. Data from five spacecraft (AMPTE/CCE, 1979-053, 1982-019, GOES-5, and GOES-6) have been used in our study. Since CCE has an apogee of 8.8 R E, those data allow for the study of both the radial and azimuthal propagation characteristics of substorm events. A list of ion injections was compiled from CCE energetic particle data obtained in 1985 and 1986. Those injections are dispersionless over an energy range of 25 keV to 285 keV on a 72-sec time scale. Dispersionless injections during which 1979-053 or 1982-019 were on the nightside in close longitudinal proximity to CCE were selected for our study. The most significant correlation in the data is between the local time separation between any two spacecraft and the time delay between the local onsets. On the other hand, in cases during which CCE was within 1 hour of local time from a geosynchronous satellite, there is little correlation between the radial separation between CCE and the geosynchronous satellite and the local onset time delay. Moreover, there is no evidence to suggest that local substorm onset propagates earthward. In fact, examination of data from several events during which there were unusually close alignments of spacecraft along the radial direction lends support to the view that local substorm onsets propagate radially outward.