Proton aurora in the cusp during southward IMF

H.U. Frey, S.B. Mende, S.A. Fuselier, T. J. Immel, N. Ostgaard


One of the most distinct aurorae in the high latitude dayside region occurs 
at the footprint of the cusp.  The Spectrographic Imager SI-12 channel on 
the IMAGE spacecraft allows for long duration observations of the proton 
aurora in this region and thus enables morphological and quantitative 
studies of the behavior of the proton aurora under different external solar 
wind conditions.  Here we extend an earlier study of the proton aurora in 
the cusp during northward interplanetary magnetic field (IMF) conditions 
[Frey et al., 2002] to southward IMF conditions.  We find a very similar 
dependence of the cusp aurora's location in magnetic local time (MLT) on the 
IMF B_y component, with locations at pre-noon for negative B_y and post-noon 
for positive B_y.  We also confirm the previously established dependence of 
the proton aurora brightness on the solar wind dynamic pressure.  However, 
the proton aurora is brighter for the southward IMF case than for the
northward IMF case.  The other major difference between southward and 
northward IMF conditions is the very strong dependence of the latitude 
location on the magnitude of the IMF B_z for southward IMF.  We discuss both 
differences in terms of the location of the reconnection site at the 
magnetopause that is connected to the ionosphere along cusp magnetic field 
lines.

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Journal of Geophysical Research, 108(A7), 1277, doi:10.1029/2003JA009861, 2003