Derivation of Auroral Conductances from IMAGE FUV

T. J. Immel (1), S. B. Mende (1), H. U. Frey (1), J.-C. Gerard (2), 
B. Hubert (2)

1 Space Sciences Laboratory, University of California Berkeley, 
  Berkeley, CA 94720
2 University of Liege, Liege, Belgium B-4000

Auroral emissions are observed in 3 separate Far-Ultraviolet (FUV) 
wavelength regimes by IMAGE. The Wideband Imaging Camera (WIC) is
sensitive mainly to N2 LBH and N I emissions in the 140-190-nm range, 
while the Spectrographic Imager (SI) spectrally separates the OI 
135.6-nm emission and doppler shifted hydrogen emissions of the 
proton aurora at 121.8 nm. The brightness of the N2 LBH and OI
135.6-nm emissions depend in part on the spectrum and total energy 
flux of incoming electrons, and on the height-density profile of 
the respective species, and O2. Due mainly to these atmospheric
factors, the ratio of the N2 and OI emissions depends strongly on
the characteristic energy of precipitating electrons which, once
estimated, can in turn be used to calculate the total energy flux.

The proton auroral generates secondary electrons, which excite
additional emissions of N2 and OI. It is not possible to absolutely 
determine either the total proton energy flux or the characteristic 
proton energy (<Ep) with a single proton imaging channel. However, 
as the proton-induced N2 and OI emissions depend most strongly on 
the total proton energy flux, reasonable estimates of <Ep can be 
used in the calculation of proton energy input. Ground-based or 
in-situ observations of proton energies can help in this 
determination.

With accurate corrections for N2 and OI airglow emissions, and
formulae such as those provided by Robinson et al. [1987], IMAGE FUV 
can provide global maps of height-integrated conductivity 
(conductance) in the auroral oval. It is also possible to examine 
the degree to which the proton aurora contributes to enhanced 
conductance on a global scale. The promise of providing these 
conductances using IMAGE's real-time capabilities will be 
discussed.

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Submitted to the Spring 2001 AGU Meeting, Boston, Massachusetts