Since some of the earliest measurements of the auroral electron spectrum at rocket altitudes were made, there has been a question about how two very distinct feaures of the spectrum can occur simultaneously. These features are (1) a spectrum peaked in energy and isotropic over all pitch angles directed into the atmosphere (the isotropic peak) and (2) intense fluxes of field aligned (FA) electrons which are usually observed at pitch angles of 10¿ or less. Recent rocket measurements with improved temporal and pitch angle resolution have added considerably to the data set on the FA component and are discussed in this paper. A summary of the characteristics of FA electrons is as follows: (1) Field-aligned electrons are associated with evening, midnight, and cusp auroras. Field aligned electrons are a common feature, seen in 8 out of 10 University of New Hampshire evening auroral rocket flights and in half of the AE satellite orbits through the cusp over a six-year period. About 80% of the S3-3 passes through the statistical auroral oval recorded field aligned electron beams. (2) Rocket data associate the field aligned electrons with active auroral forms and on the edges of moving discrete arcs, predominantly the leading edge. Occasionally they are observed between bright auroral forms. (3) The spatial/temporal scale of field aligned events seen by satellites is a few seconds or tens of kilometers. The rocket data time scale extends from seconds to hundreds of seconds.

When bursts of field aligned electrons appear, they may be due to incomplete energy and/or pitch angle coverage by the detectors. The intensity of field aligned electrons has been observed to oscillate at a few hertz. (4) At any given time the electrons are field aligned over a wide range of energies, often extending from the peak energy in the isotropic Maxwellian population that coexists with the field aligned electrons to very low energies. On occasion the field aligned electrons terminate at low energies in an isotropic halo. (5) Because of the high degree of field alignment and the restriction to low energies, the field aligned population does not deposit appreciable energy into the ionosphere but can be a significant current carrier. (6) At satellite altitudes of 3000-8000-km, precipitating field aligned electrons are often associated with up-streaming field aligned electrons and conic ion distributions. At satellite altitudes, field aligned electrons are also observed on the edges of ion inverted-V structures. Recent rocket data have revealed field alignment of auroral electrons up to 15-keV energy. The differential intensity of these electrons is very intense and gives no evidence for acceleration by static field aligned electric fields. These field aligned electrons are observed to have a distribution function very similar to that for electrons injected at synchronous orbit during substorms. Recent acceleration mechanisms involving turbulence are discussed.