[en] Atmospheric Composition and Structure: Thermosphere-energy deposition ; Atmospheric Composition and Structure: Airglow and aurora ; Magnetospheric Physics: Energetic particles ; precipitating ; Magnetospheric Physics: Storms and substorms
[en] The IMAGE satellite carries three FUV imagers observing N[SUB]2[/SUB] LBH, O I 1356 Å, 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 N[SUB]2[/SUB] LBH and O I 1356 Å 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.