Morphology and seasonal variations of global auroral proton precipitation 
observed by IMAGE-FUV

Valerie Coumans, Jean-Claude Gerard, Benoit Hubert, Stephen B. Mende, 
and Stanley W. H. Cowley


Observations with the FUV imagers on board the IMAGE satellite have been used to
map the auroral electron and proton energy fluxes during the summer and winter
solstices of 2000, in order to construct a statistical view of the global
auroral proton precipitation. The distribution for electrons compare well both
in morphology and in magnitude with those obtained previously with the Polar-UVI
instruments and with an empirical auroral precipitation model based on DMSP
data. The proton morphology also closely resembles the statistical ion oval
derived from DMSP data, showing a ÒC-shapedÓ morphology with a minimum located
in the morning sector. The precipitation proton auroral power is on the order of
2.2 GW for an average Kp value of 2, also in close agreement with the values of
the DMSP empirical model. The FUV data also reveal the presence of seasonal
effects in the proton precipitation. Specifically, the latitudinal width of the
proton oval is larger in summer than in winter so that the globally precipitated
proton power is 1.5 times higher in summer than in winter. The occurrence
probability of intense proton auroras (with energy flux >0.5 mW m-2) is also
shown to be nearly three times higher in summer than in winter. This seasonal
effect in the proton precipitation contrasts with those observed for electrons,
where intense electron events occur more often in winter than in summer. We
discuss a mechanism that may account for these results based on the presence of
field-aligned potential drops which accelerate auroral electrons downward in
regions of upward directed field-aligned current, while suppressing the
precipitating magnetospheric proton flux. The presence of such field-aligned
potentials is dependent on the differing solar illumination in winter and
summer.

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Journal of Geophysical Research, 109, A12205, doi:10.1029/2003JA010348, 2004