The dc and ac electric field, plasma density, plasma temperature, and field‐aligned current experiments on the S3‐3 satellite

Measurements of dc electric fields, field‐aligned currents, the plasma density, and wave electric fields and density fluctuations have been made for the first time at auroral zone altitudes between 1000 and 8000 km on the S3‐3 satellite. The design and operation of the various detectors that made these measurements is described, and some typical scientific results are presented. These include the observations that the high altitude auroral zone plasma density is typically 5–50 particles/cm³, that field‐aligned currents exceeding the electrostatic ion cyclotron instability threshold are often observed in regions of ion cyclotron wave emission and accelerated upgoing ions, that the auroral zone electric field penetrates the plasmapause to cause deviations from corotation of the plasmasphere, and that the energetic electron high latitude trapping boundary is sometimes equatorward of the last closed magnetic field line, as determined by the reversal in the poleward electric field component.