Characterization and dynamics of the auroral electron precipitation during 
substorms deduced from IMAGE-FUV

M. Meurant, J.C. Gerard, B. Hubert, V. Coumans, V.I. Shematovich, D.V. Bisikalo, 
D.S. Evans, G.R. Gladstone, and S. B. Mende


The FUV imager on board the IMAGE satellite provides simultaneous images of the
north polar aurora every 2 min in three spectral channels. The Wideband Imaging
Camera (WIC) responds primarily to the N2 LBH bands while one of the Spectral
Imagers (SI13) includes the OI 135.6 nm emission and nearby LBH bands. The third
channel (SI12) is sensitive to Doppler-shifted Lyman-alpha emission at 121.8 nm
generated by proton precipitation. The relative magnitude of the WIC and SI13
signals depends on the altitude distribution of the energy deposition, in
response to the differential O2 absorption and the altitude dependence of the
neutral composition. The ratio of simultaneous images from WIC and SI13 is used
to derive the spatial distribution of the characteristic energy of the
precipitating auroral electrons and the energy flux they carry. The method is
described and the uncertainties introduced by possible perturbations of the
neutral composition known to occur in the auroral thermosphere are discussed.
The first part of this study describes a validation of this method performed by
comparing precipitation characteristics derived from FUV with in situ
measurements from two coincident passes of the NOAA-16 satellite. They are shown
to agree within about 45%. The second part applies this ratio method to analyze
the time evolution of auroral activity which occured during two substorms on 28
October 2000. The time evolution is displayed in the form of magnetic local time
and magnetic latitude keograms. It is shown that the pattern of the electron
average energy distribution exhibits both spatial and temporal changes.
Comparison with FAST in situ electron spectrograms confirms the ability of IMAGE
to detect precipitation events with a ~200 km spatial scale. However the
characteristics of the physical process leading to electron acceleration cannot
be identified with FUV. The highest values of the average energy are colocated
in time and space with the largest electron precipitation fluxes. A dawnward
motion of bright features is observed in the postmidnight at speeds on the order
of 5 magnetic local time hours/UT hour. 

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Journal of Geophysical Research 108 (A6), 1247, doi: 10.1029/2002JA009685, 2003