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Height-integrated conductance and field-aligned current magnitudes evolve differently during a substorm
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  • Jennifer Alyson Carter,
  • Steve Milan,
  • Colin Forsyth,
  • Mark Lester,
  • Maria-Theresia Walach,
  • Jesper W. Gjerloev,
  • Larry J. Paxton,
  • Brian J. Anderson
Jennifer Alyson Carter
University of Leicester

Corresponding Author:[email protected]

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Steve Milan
University of Leicester
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Colin Forsyth
University College London
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Mark Lester
University of Leicester
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Maria-Theresia Walach
Lancaster University
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Jesper W. Gjerloev
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Larry J. Paxton
Johns Hopkins University
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Brian J. Anderson
John Hopkins Univ.
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We examine the average evolution of precipitation-induced
height-integrated conductances, along with field-aligned currents, in
the nightside sector of the polar cap over the course of a
substorm. Conductances are estimated from the average energy flux and
mean energies derived from auroral emission data. Data are binned
using a superposed epoch analysis on a normalised time grid based on
the time between onset and recovery phase ($\delta$t) of each
contributing substorm. We also examine conductances using a fixed time
binning of width 0.25 hr. We split the data set by magnetic latitude
of onset. We find that the highest conductances are observed for
substorms with onsets that occur between 63 and 65 degrees magnetic
latitude, peaking at around 11 mho (Hall) and 4.8 mho
(Pedersen). Substorms with onsets at higher magnetic latitudes show
lower conductances and less variability. Changes in conductance over
the course of a substorm appear primarily driven by changes (about 40%
at onset) in the average energy flux, rather than the average energy
of the precipitation. Average energies increase after onset slower
than energy flux, later these energies decrease slowly for the lowest
latitude onsets. No clear expansion of the main region 1 and region 2
field-aligned currents is observed. However, we do see an ordering of
the current magnitudes with magnetic latitude of onset, particularly
for region 1 downwards FAC in the morning sector. Peak current
magnitudes occur slightly after or before the start of the recovery
phase for the normalised and fixed-time grids.