The auroral acceleration region: The world of beams, conies, cavitons, and other plasma exotica

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Abstract
The aurora is the most visible manifestation of the energetic plasma in the Earth's magnetosphere and its interaction with the atmosphere. For a brief history of aurora and excellent references to early theories one is referred to Chapman [1967]. It has long been recognized that the direct cause of the aurora is the precipitation of energetic (keV) electrons and ions into the atmosphere leading to excitation of the ambient atmospheric gases which then emit light characteristic of their chemical composition. However, early in the history of space physics it was recognized that the auroral process was far more complex than the simple guiding of energetic charged particles from the sun to the atmosphere by the Earth's magnetic field lines. Balloon measurements of x‐rays with energies up to 70 keV in association with active aurorae [Winckler et al., 1958] implied that electrons were accelerated to energies large compared to those of solar wind electrons. Figure 1 shows schematically many of the features and processes that we now associate with active aurorae.