Open AccessAuroral particle acceleration by strong double layers: The upward current region
Author(s) -
Ergun R. E.,
Andersson L.,
Main D.,
Su Y.J.,
Newman D. L.,
Goldman M. V.,
Carlson C. W.,
Hull A. J.,
McFadden J. P.,
Mozer F. S.
Publication year - 2004
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2004ja010545
Subject(s) - electric field , physics , particle acceleration , electron , acceleration , computational physics , geophysics , amplitude , classical mechanics , optics , quantum mechanics
Satellite observations have established that parallel electric fields of both upward and downward current regions of the aurora are supported, at least in part, by strong double layers. The purpose of this article is to examine the role of double layers in auroral electron acceleration using direct measurements of parallel electric fields and the accompanying particle distributions, electrostatic waves, and nonlinear structures; the concentration is on the upward current region. Direct observations of the ionospheric boundary of the auroral cavity suggest that a stationary, oblique double layer carries a substantial, albeit a minority fraction (∼10% to ∼50%) of the auroral potential. An order of magnitude density gradient results in an asymmetric electric field signature. Oblique double layers with amplitudes greater than 100 mV/m have been verified in ∼3% and may occur in up to 11% of auroral cavity crossings, so it is feasible that strong double layers are a principal acceleration mechanism. In this article we also present a second type of double layer that has a symmetric electric field signature and is seen inside of the auroral cavity. These structures are a possible signature of a midcavity or high‐altitude acceleration mechanism. Numerical solutions of the Vlasov‐Poisson equations support the possibility of midcavity double layers and indicate that trapped electrons can play an important role in the double‐layer structure.