Energetic neutral atom imaging with the POLAR CEPPAD/IPS instrument: Initial forward modeling results

Although the primary function of the CEP-PAD/TPS instrument on Polar is the measurement of energetic ions in-situ, it has also proven to be a very cap able Energetic Neutral Atom (ENA) imager. Raw ENA images are currently bein g constructed on a routine basis with a temporal resolution of minutes duri ng both active and quiet times. However, while analyses of these images by themselves provide much information on the spatial distribution and dynamic s of the energetic ion population in the ring current, detailed modeling is required to extract the actual ion distributions. In this paper, we presen t the initial results of forward modeling an IFS ENA image obtained during a small gee-magnetic storm on June 9, 1997. The equatorial ion distribution inferred with this technique reproduces the expected large noon/midnight a nd dawn/dusk asymmetries. The limitations of the model are discussed and a number of modifications to the basic forward modeling technique are propose d which should significantly improve its performance in future studies. (C) 1998 Elsevier Science Ltd. All rights reserved.