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Downward auroral currents from the reconnection Hall-region + Corrigendum

Treumann, R. A., R. Nakamura, and W. Baumjohann (2011), Downward auroral currents from the reconnection Hall-region + Corrigendum, Annales Geophysicae, 29, 679-685, doi:10.5194/angeo-29-679-2011 and 10.5194/angeo-29-1061-2011, See also the Corrigendum on p. 1061.

We present a simple (stationary) mechanism capable
of generating the auroral downward field-aligned electric
field that is needed for accelerating the ionospheric electron
component up into the magnetosphere and confining the
ionospheric ions at low latitudes (as is required by observation
of an ionospheric cavity in the downward auroral current
region). The lifted ionospheric electrons carry the downward
auroral current. Our model is based on the assumption of
collisionless reconnection in the tail current sheet. It makes
use of the dynamical difference between electrons and ions
in the ion inertial region surrounding the reconnection X-line
which causes Hall currents to flow. We show that the spatial
confinement of the Hall magnetic field and flux to the
ion inertial region centred on the X-point generates a spatially
variable electromotive force which is positive near the
outer inflow boundaries of the ion inertial region and negative
in the central inflow region. Looked at from the ionosphere
it functions like a localised meso-scale electric potential.
The positive electromotive force gives rise to upward
electron flow from the ionosphere during substorms (causing
“black aurorae”). A similar positive potential is identified
on the earthward side of the fast reconnection outflow region
which has the same effect, explaining the observation that auroral
upward currents are flanked from both sides by narrow
downward currents.
Further information
  author = {R. A. Treumann and R. Nakamura and W. Baumjohann},
  journal = {Annales Geophysicae},
  month = {apr},
  note = {See also the Corrigendum on p. 1061},
  pages = {679-685},
  title = {{Downward auroral currents from the reconnection Hall-region + Corrigendum}},
  volume = {29},
  year = {2011},
  url = {www.ann-geophys.net/29/679/2011/},
  doi = {10.5194/angeo-29-679-2011 and 10.5194/angeo-29-1061-2011},
%0 Journal Article
%A Treumann, R. A.
%A Nakamura, R.
%A Baumjohann, W.
%D 2011
%V 29
%J Annales Geophysicae
%P 679-685
%Z See also the Corrigendum on p. 1061
%T Downward auroral currents from the reconnection Hall-region + Corrigendum
%U www.ann-geophys.net/29/679/2011/
%U www.ann-geophys.net/29/1061/2011/
%8 apr
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