Rocket-borne measurements of the dayside cleft plasma: The Tordo Experiments

Results are presented from low-energy plasma analyzers (12 eV to 12 keV) carried on two rockets launched into the dayside cleft during January 1975. We conclude that (1) atmospheric interaction becomes important for <1-keV electrons at approximately 250 km, (2) characteristics of particles in ‘inverted V's’ observed in the afternoon cleft are consistent with their interpretation as being due to parallel electric field acceleration from a constant source population, and (3) magnetospheric ‘energetic’ (>2 keV) electrons intermingle with ‘magnetosheathlike’ plasma in the cleft.