Simultaneous ENA Observations of Ring Current Injection from IMAGE and POLAR

Reeves, G. D., M. G. Henderson, R. M. Skoug, H. O. Funsten, M. F. Thomsen, 
C. J. Pollock, J.-M. Jahn, D. J. McComas, J. B. Blake, J. F. Fennell, H. E. Spence, 
D.G. Mitchell, E. C. Roelof, and the POLAR and IMAGE teams 

The IMAGE Medium Energy Neutral Atom (MENA) instrument and the POLAR Imaging Proton Sensor 
(IPS) provide highly-complementary views of the magnetosphere. MENA measures magnetospheric 
neutral atoms in the energy range from approximately 1 to 30 keV with 4 deg x 4 deg angular 
resolution. IPS measures protons and neutral hydrogen with energies above 20 keV with 
approximately 11 deg x 20 deg resolution.  POLAR/IPS has proven to be a very capable 
energetic neutral atom imager when POLAR is located on field lines with few or no energetic  
protons. Since the instruments are quite different they do not give a true stereo ENA view 
of the magnetosphere such as TWINS will provide, but they do provide the first simultaneous 
ENA images of the magnetosphere from two separate vantage points. We have examined the two 
data sets simultaneously for a moderate geomagnetic storm that took place on August 12, 2000 
in order to investigate the injection of particles from the plasmasheet into the ring 
current. We have also used forward-modeling techniques to obtain the trapped magnetospheric  
ion distributions and use those models to further compare information contained in the two 
sets of ENA images separately and in combination. 

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Presented at the Fall American Geophysical Union Meeting, 
San Francisco, CA., December 15-19, 2000