IMAGE/LENA Observations of Neutral Atoms from the Solar Wind

Collier, M.R., et al.

We report observations of neutral atoms from the solar wind in the Earth's 
vicinity with the Low Energy Neutral Atom (LENA) imager on the IMAGE 
(Imager for Magnetopause-to-Aurora Global Exploration) spacecraft.  This 
instrument was specifically designed to be capable of looking at and in the 
direction of the Sun. Enhancements in the hydrogen count rate in about the 
solar direction are correlated with neither solar ultraviolet emission nor 
suprathermal particles and must therefore be due to neutral particles from 
the solar wind. LENA observes these particles from the direction closest to 
that of the Sun even when the Sun is not directly in LENA's field of view. 
Based on simulations, these neutrals are the result of solar wind ions 
charge exchanging with the exospheric neutral hydrogen atoms in the 
post-shock flow of the solar wind in the magnetosheath. We consider a 
variety of sources for the neutral particles observed when the Sun is 
within LENA's field of view including solar wind charge exchange with dust 
grains and interstellar neutrals and undisturbed solar wind and 
magnetosheath charge exchange with the Earth's geocorona. We will compare 
the LENA results to previous theoretical work and modeling work.