Medium Energy Neutral Atom (MENA) Imaging of Magnetospheric Substorms
 
J. Jahn, C. Pollock, M. Wuest, D. McComas, J. Burch, R. Friedel, R. Skoug, M. Thomsen, 
M. Henderson 

The Medium Energy Neutral Atom Imager (MENA) on the IMAGE spacecraft provides
images of energetic neutral atom emissions (ENA's) in the inner magnetosphere for
energies of 1.0 to about 30 keV. Early results show that MENA is highly suited to study ENA
emissions related to substorm injection events. The unique energy range covered by MENA
enables us to study the different dynamics of low energy (few keV) to medium energy
(10's of keV) particle populations simultaneously with the same instrument. We will
present MENA imaging data from a variety of isolated substorms, focusing on the
morphology and time development of ENA emissions at all energies covered by MENA. ENA
emissions will be compared with in situ plasma measurements at geosynchronous
altitudes and from the POLAR spacecraft. This comparison constitutes an early attempt to
introduce in situ ground-truth comparisons to ENA imaging measurements in the
equatorial plane and at high-latitude locations in the magnetosphere. It also provides an
opportunity to discuss the projection effects ENA observations that are due to the pitch
angle distributions of the ENA producing ion populations. We will elaborate on the
potential and the challenges resulting from these viewing effects for ENA imaging of
magnetospheric substorms and other magnetospheric processes.

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