Cusp studies with IMAGE-FUV

H.U. Frey, S.B. Mende, S.A. Fuselier, J.-C. Gerard, B. Hubert, G.R. Gladstone, 
C.W. Carlson

The FUV instrument on IMAGE frequently observes localized ultraviolet emission
on the high latitude dayside, poleward of the normal auroral oval location. This
emission is especially distinct in the observations of Doppler shifted Lyman
alpha emission from precipitating protons. We interpret this emission as the
optical signature of precipitation into the cusp after lobe reconnection at the
magnetopause.

Several cusp crossings by the FAST satellite are used to establish an estimate
of the energy input and the characteristics of the precipitating protons.
Multivariate cluster analysis and other statistical tools are used to determine
the dependence of this precipitation on solar wind parameters. This shows that
under northward IMF and high solar wind dynamic pressure, proton precipitation
can be the dominating energy input into the cusp region.

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Submitted to the Spring 2001 AGU Meeting, Boston, Massachusetts