DE‐1 observations of counterstreaming electrons at high altitudes

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Abstract
Observations of plasma at altitudes of 2‐3 RE with the High Altitude Plasma Instrument (HAPI) on DE‐1 indicate two distinct types of counterstreaming electron events. The type 1 event is characterized by two Maxwellian distribution functions, an isotropic high‐temperature component and a field‐aligned low temperature component. The type 2 event is distinguished by beams parallel and antiparallel to the magnetic field direction. The observations suggest two distinct mechanisms for accelerating counterstreaming electrons. Type 1 events appear to involve wave‐particle interactions while type 2 events imply direct acceleration by oppositely‐directed electric fields pointing toward the satellite along magnetic field lines.