THE ELECTRON SIGNATURE OF PARALLEL ELECTRIC-FIELDS

Electron distribution functions measured on the Dynamics Explorer 1 spacecraft are shown to have the characteristics expected in a region of parallel electric fields. In a previous study we have shown that the distributions typically observed at altitudes near and above an altitude of one earth radius over the auroral oval are indicative of field-free regions between regions of parallel acceleration above and below the observation point. Test-particle simulations show that electron distributions resembling bi-directional conics are expected to occur in regions of parallel electric fields, and this type of distribution has been observed with the High Altitude Plasma Instrument aboard the Dynamics Explorer 1 spacecraft.