The electron and proton energy input into the auroral thermosphere during 
substorms: Remote sensing with IMAGE-FUV

B. Hubert (1), J.C. Gerard (1), M. Meurant (1), D.S. Evans (2), S.B. Mende (3),
H.U. Frey (3) and T.J. Immel (3)

(1) Laboratoire de Physique Atmospherique et Planetaire, Universite de Liege, 
    Belgium
(2) NOAA Space Environment Center, Boulder, Colorado
(3) Space Sciences Laboratory, University of California, Berkeley

The IMAGE satellite carries three FUV instruments globally imaging the N2-LBH,
OI-1356 A and HI Lyman-alpha emissions in the north polar aurora. The time 
variations of 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 other two images are combined to determine 
the distribution of 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 in the thermosphere carried by 
the protons and electrons separately. The time development of the proton and 
electron aurora during several winter solstice events is examined. Although the 
onsets of the proton and electron aurora coincide in time and space, the times 
of the peak of energy dissipation 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 energy hemispheric power 
on magnetic activity measured by NOAA-15. The hemispheric power deduced from 
the FUV images also compares favorably to the NOAA-deduced values, except 
during periods of fast variations. The time variation of the electron and 
proton energy input in different MLT sectors will also be examined in the 
course of the substorm development and recovery phases.

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To be presented at the EGS Meeting, Nice, France, April 22, 2002