The figure shows the equatorial ring current proton distribution in
the 50-60 keV range during the storm main phase of 4 October 2000,
18:00 UT, obtained by the High Energy Neutral Atom (HENA) imager on
board the IMAGE spacecraft. The distribution was extracted from a raw
Energetic Neutral Atom (ENA) image by applying a constrined linear
inversion algorithm assuming a dipole magnetic field and pitch angle
isotropy. The classical main phase ring current was believed to peak
around dusk.  This observation is consistent with ring current model
results by R. A. Wolf et al.  and M. -C. Fok et al. and confirms that
the observed eastward skewing is an effect of the strong coupling
between the partial ring current and the ionosphere via the region 2
current system that modifies the electric field in the magnetosphere.