Ring Current Ion Distributions From Dual Vantage Point ENA Images

Energetic neutral atom (ENA) imaging has been exploited for several years as a tool for observing the global energetic ion morphology and dynamics in the storm-time ring current. Inversion of ENA images to obtain the parent ring current ion distributions has, however, met with limited success. Although the local time variation in ring current ions is often extracted, the ion pitch-angle distributions are more difficult, or impossible, to obtain; the ENA images do not contain sufficient information to uniquely determine the ion pitch-angles. The pitch-angle distributions of ring current ions reveal much about the processes that control ring current decay: interaction with the plasmasphere can drive waves and pitch-angle scatter the ring current ions into the loss cone; current sheet scattering may also play an important role in modifying the ion pitch-angles. With the anticipation of the TWINS mission, we are investigating the extent to which simultaneous ENA images from two separate vantage points can provide the additional information required to obtain pitch-angle distributions, along with the ion spatial distributions. In this talk we will report on efforts to invert ENA images from the IMAGE High Energy Neutral Atom imager, HENA, taken from different locations in the IMAGE orbit. Although such images are necessarily not simultaneous, we restrict the analysis to the recovery phase of major storms, during intervals when there is no additional solar wind energy input. During such times, the ion distributions should be slowly evolving, and we approximate them as stationary over the interval between the two selected HENA images. Early results suggest that dual vantage point imaging will improve the inversion of the ion distributions, including the ion pitch-angle distributions.