Origins and Consequences of Parallel Electric Fields

Abstract

Over the past two decades there have been serious debates concerning the roles of parallel electric fields (EM_II) in the formation of aurorae. That such electric fields exist has been observationally established only in the last five years (Mozer et al., 1980). Early proponents of the pro-E_II case pointed to the nearly monoenergetic beams of keV electrons observed above auroral arcs. Opponents argued against E_I on both theoretical and observational grounds. Theoretically, it was argued that if significant field-aligned potential drops ever develop, then highly mobile ionospheric or magnetospheric electrons would move quickly to discharge them. Since the discharge time would be in the order of seconds and arcs persist on time scales of up to an hour, E_I must not be a major source of auroral energy. Plasma theorists were quick to point out that collective effects can significantly alter the mobility of electrons along magnetic field lines. Parallel potential drops arising from anomalous resistivity and double-layer phenomena are frequently observed in laboratory plasmas. However, questions of scaling differences between laboratory and space plasmas rendered such arguments conclusive mainly to their proponents.