Current carriers for the field-aligned current system

Abstract

Recently the Dynamics Explorer satellites have returned a large body of data containing high resolution magnetometer measurements and distributions of charged particles of all but thermal electrons. From these data a systematic study has begun of the relations of the field-aligned currents to particle precipitation structures and the identification of the charge carriers. The data have been separated into three levels of magnetic activity and three local time sectors. Results of this study include the following: 1. During very quiet periods, field-aligned currents exist primarily as fine structure. 2. During onset of substorms, Region 1 and Region 2 become clearly evident but contain significant structure. 3. As magnetic activity subsides, current regions become less distinct, and structure becomes more dominant. 4. The distribution of the upward currents derived from magnetometer data and calculated from suprathermal electron data agree remarkably well in shape but not necessarily in magnitude. 5. At all local times, >5 eV electrons seldom carry most of the upward current. 6. Except for the accelerated Inverted-V electrons, the dominant upward current carriers which are measured are below 500 eV and are distributed in energy. 7. Dusk upward currents (Region 1) are associated with the Boundary Plasma Sheet (BPS). 8. Suprathermal electron bursts are important current carrying structures.