GLOBAL CHARACTERISTICS OF PARTICLE-PRECIPITATION AND FIELD-ALIGNED ELECTRON ACCELERATION DURING ISOLATED SUBSTORMS

Global features of particle precipitation and field-aligned electron acceleration during isolated substorms were investigated using energetic particle data from the DMSP F6 and F7 satellites. The onset time and the recovery phase of each isolated substorm were determined using both the AU and AL indices and low-latitude Pi 2 magnetic pulsations. It is found that during the recovery phase the poleward edge of the precipitation region of central plasma sheet (CPS) type electrons expands to latitudes higher than 72-degrees around midnight, while the equatorward boundary of this region expands to latitudes lower than those before the substorm onset in the postmidnight sector of 00-06 MLT. In the recovery phase, many accelerated electron precipitation events were embedded in the CPS-type electron precipitation region for the nightside local times from 18 MLT to 09 MLT. Several different kinds of latitudinal dispersion of electron and ion energy were observed near the lowest latitude of the particle precipitation region. The features vary significantly depending on the magnetic local time. These energy dispersion features can be explained by injected particle motions in the magnetosphere. These energy dispersion features also show a possibility of some particle injections in the magnetotail even before the substorm onset. The field-aligned potential differences, estimated from the peak energy of accelerated electron energy spectra, do not change on the morningside before and after the substorm onset, while they increase up to several kilovolts on the eveningside during the recovery phase. On the other hand, the field-aligned potential differences were estimated for the accelerated electron precipitation events embedded in the CPS-type electron precipitation region and were found to be slightly larger on the morningside than on the eveningside during the recovery phase. These features of field-aligned potential differences can be explained by assuming that the field-aligned electric field is formed to maintain the large-scale region I and II currents. The electron densities above the field-aligned potential difference were also estimated from an accelerated Maxwellian fitting procedure. They do not change clearly before the onset and in the recovery phase. This fact suggests that the supply and loss of electrons into the loss cone at magnetospheric altitudes are balanced during the substorms.