Electron and proton excitation of the FUV aurora: Simultaneous IMAGE and NOAA 
observations

V. Coumans, J.-C. Gerard, B. Hubert, and D. S. Evans


The Far Ultraviolet (FUV) imaging system on board the IMAGE satellite provides a
global view of the north auroral region in different spectral channels. The
Wideband Imaging Camera (WIC) is sensitive to the N2 LBH emission and NI
emissions produced by both electron and proton precipitations. The SI12 camera
images the Lyman-a emission due to incident protons only. We compare WIC and
SI12 observations with model predictions based on particle measurements from the
TED and the MEPED detectors on board NOAA-TIROS spacecraft. Models of the
interaction of auroral particles with the atmosphere are used together with the
in situ proton and electron flux and characteristic energy data to calculate the
auroral brightness at the magnetic footprint of the NOAA-15 and NOAA-16 orbital
tracks. The MEPED experiment measures the precipitating particles with energy
higher than 30 keV, so that these comparisons include all auroral energies, in
contrast to previous comparisons. A satisfactory agreement in morphology and in
magnitude is obtained for most satellite overflights. The observed FUV-WIC
signal is well modeled if the different spatial resolution of the two sensors is
considered and the in situ measurements properly smoothed. The calculated count
rate includes contributions from LBH emission, the NI 149.3 nm line, and the OI
135.6 nm line excited by electrons and protons. The proton contribution in WIC
can locally dominate the electrons. The comparisons indicate that protons can
significantly contribute to the FUVaurora at specific times and places and
cannot be systematically neglected. The results confirm the shift of the proton
auroral oval equatorward of the electron oval in the dusk sector. We also show
that in some regions, especially in the dusk sector, high-energy protons
dominate the proton energy flux and account for a large fraction of the Lyman-a
and other FUV emissions.  

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Journal of Geophysical Research, 107(A11), 1347, doi:10.1029/2001JA009233, 2002