Inverse electron energy dispersion from moving auroral forms. Issue 12 (22nd December 2016)

• Record Type: Journal Article
• Authors: Cameron, Taylor; Knudsen, David
• Is Part Of: Journal of geophysical research. Volume 121:Issue 12(2016:Dec.)
• Page Start: 11, 896
• Page End: 11, 911
• Publication Date: 2016-12-22
• Subjects: auroral -- electron -- acceleration; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2016JA023045
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Numerous published examples of energy‐dispersed bursts show electron energies reaching as high as several keV and decaying to lower energies over a fraction of 1 s. This signature has been interpreted by some authors as due to impulsive acceleration to a broad range of energies in a localized region and by others as the result of impulsive, dispersive Alfvén waves, in which case the acceleration takes place over an extended distance along magnetic field lines. A survey by the Suprathermal (0–350 eV) Electron Imager on the Enhanced Polar Outflow Probe (ePOP) in the topside ionosphere has produced examples of high‐to‐low ("regular") energy dispersion, but also a smaller number of examples exhibiting low‐to‐high ("inverse") dispersion, which to our knowledge has not been reported before. Motivated by a recent report of regular electron dispersion produced by auroral rays moving faster than theE ×B drift speed, we investigate a heuristic model of electron acceleration within a region of uniform electric field parallel toB which extends a distance L a along magnetic field lines. We show that in addition to a broad range of energies, this model produces inverse dispersion when the detector is less than L a beneath the bottom of the acceleration region and regular dispersion for detector distances larger than L a . This simple model is meant to inform future efforts to construct a more physical model of suprathermal electron acceleration within moving auroral forms and suggests that inverse dispersion indicates relative proximity to an altitude‐extended acceleration region. Key Points: Low‐to‐high "inverse" electron energy dispersion is observed on the ePOP satellite Inverse dispersion can result from a moving localized acceleration region extended alongB The ePOP SEI instrument records 2‐D electron distributions at 100 images per second