IMAGE/HENA/SSD Low-Altitude ENA Images in Coordination with High-Resolution Pitch Angle 
Observations from POLAR/SEPS

H D Voss (1) (HNVOSS@tayloru.edu) D G Mitchell (2), E C Roelof (2),  K C Hsieh (3), 
C C Curtis (3), D C Hamilton (4), M Walt (5)  , W Toll (1)

1 Taylor University, Physics Dept., Upland, IN, 46989, United States
2 John Hopkins University/Applied Physics Lab, Laurel, MD 20723
3 University of Arizona, Tucson, AZ, 85721,United States
4 University of Maryland, College Park, MD, 20742, United States
5 Star Laboratory, Stanford University, Stanford, CA, 94305, United States

New composition images from the IMAGE High Energy Neutral Atom (HENA) Solid State Detector 
(SSD) indicate strong ENA emission from ions at low altitudes near the auroral oval. The 
SSD sensor on IMAGE consists of 240 pixels with time-of-flight and energy analysis between 
30 and 300 keV. Energetic hydrogen, helium, and CNO are resolved well in the data. The 
remotely sensed altitude variation of the ENA is consistent with energetic ions that become 
charge exchanged in the upper atmosphere [see Roelof et al., this Conference]. The altitude 
variation of the ENA imaged near perigee is strongly dependent on the ion angular 
distribution.  High angular resolution pitch-angle distributions of E>120 keV protons 
obtained by the CEPPAD/SEPS SSD high angular resolution imaging spectrometer on the NASA 
POLAR satellite are analyzed to compare with the ENA and to estimate pitch-angle losses. 
Several small magnetic storms in May 2000 were selected for analysis, because the orbit 
planes of IMAGE and POLAR were similar and both were near perigee for the inter-comparison. 
ENA images, composition, insitu proton distributions, modeling, and other measurements all 
contribute to understanding the mechanisms associated with the ion aurora.

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