Total electron and proton energy input during auroral substorms: Remote sensing 
with IMAGE-FUV

B. Hubert and J.-C. Gerard
Laboratoire de Physique Atmospherique et Planetaire, Universite de Liege,
Liege-Ougree, Belgium

D. S. Evans
NOAA Space Environment Center,
Boulder, Colorado, USA

M. Meurant
Laboratoire de Physique Atmospherique et Planetaire, Universite de Liege,
Liege-Ougree, Belgium

S. B. Mende, H. U. Frey, and T. J. Immel
Space Sciences Laboratory, University of California,
Berkeley, California, USA


The IMAGE satellite carries three FUV imagers observing N2 LBH, O I 1356
angstrom, and HI Lyman alpha emissions in the polar aurora. These simultaneous
observations are used to characterize the precipitating electron and proton
energy fluxes. The proton energy flux is derived from the Lyman alpha
measurements on the basis of efficiency curves calculated with a Monte Carlo
simulation of the proton aurora. The resulting proton contribution to the N2 LBH
and O I 1356 angstrom emissions is calculated and subtracted to obtain the
electron contribution in the other two channels. These two quantities are used to
determine the precipitating electron average energy and energy flux. The proton
and electron energy fluxes are integrated over the hemisphere to obtain the rate
of auroral energy dissipation (hemispheric power) carried by the protons and
electrons separately. The time development of the proton and electron aurora
during four winter time events is examined. Although the onsets of the proton and
electron aurora coincide in time and space, the time of the peak of energy
dissipation and the recovery time are often found to differ. The fractional
energy flux carried by the protons is highest during quiet periods and reaches a
minimum during the most active phase of the substorms. This result is in
agreement with the dependence of the fractional proton hemispheric power on
magnetic activity measured by NOAA 15. The hemispheric power deduced from the FUV
images is compared to the NOAA-deduced values and found to be in reasonable
agreement. Sources of uncertainties in the determination of the hemispheric power
are discussed on the basis of several sensitivity tests. In particular, it is
found that the most critical factor is the assumption made on the energy of the
auroral protons if this energy is <25 keV. 

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J. Geophys. Res., 107, A8, 2002.