Heliosphere-Geosphere Interactions Using Low Energy Neutral Atom Imaging

T.E. Moore, M.R. Collier, M.-C. Fok, S.A. Fuselier, H. Khan, W. Lennartsson, 
D.G. Simpson, G.R. Wilson and M.O. Chandler


Development of the low energy neutral atom (LENA) imager was originally
motivated by a need to remotely sense plasma heating in the topside ionosphere,
with the goal of greatly enhanced temporal resolution of an otherwise familiar
phenomenon. During ground test and calibration, the LENA imager was found to
respond to neutral atoms with energies well above its nominal energy range of
10Ð750 eV, up to at least 3Ð4 keV, owing to sputtering interactions with its
conversion surface. On orbit, LENA has been found to respond to a ubiquitous
neutral atom component of the solar wind, to the neutral atoms formed by
magnetosheath interactions with the geocorona during periods of high solar wind
pressure, and to the interstellar neutral atoms flowing through the heliosphere
during the season of maximal relative wind velocity between spacecraft and
interstellar medium. LENA imaging has thus emerged as a promising new tool for
studying the interplanetary medium and its interaction with the magnetosphere,
in addition to the ionospheric heating and outflow that result from this
interaction. LENA emissions from the ionosphere consist of a fast component that
can be observed at high altitudes, and slower components that evidently create a
quasi-trapped extended superthermal exosphere. The more energetic emissions are
responsive to solar wind energy inputs on time scales of a few minutes.

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Space Science Reviews, 109 (1-4), 351-371, 2003