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Helium escape from the Earth's atmosphere - The charge exchange mechanism revisitedWe have studied the escape of neutral helium from the terrestrial atmosphere through exothermic charge exchange reactions between He(+) ions and the major atmospheric constituents N2, O2 and O. Elastic collisions with the neutral background particles were treated quantitatively using a recently developed kinetic theory approach. An interhemispheric plasma transport model was employed to provide a global distribution of He(+) ions as a function of altitude, latitude and local solar time and for different levels of solar ionization. Combining these ion densities with neutral densities from an MSIS model and best estimates for the reaction rate coefficients of the charge exchange reactions, we computed the global distribution of the neutral He escape flux. The escape rates show large diurnal and latitudinal variations, while the global average does not vary by more than a factor of three over a solar cycle. We find that this escape mechanism is potentially important for the overall balance of helium in the Earth's atmosphere. However, more accurate values for the reaction rate coefficients of the charge exchange reactions are required to make a definitive assessment of its importance.
Document ID
19930044389
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Lie-Svendsen, O.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Rees, M. H.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Stamnes, K.
(Alaska Univ. Fairbanks, United States)
Date Acquired
August 16, 2013
Publication Date
December 1, 1992
Publication Information
Publication: Planetary and Space Science
Volume: 40
Issue: 12
ISSN: 0032-0633
Subject Category
Geophysics
Accession Number
93A28386
Funding Number(s)
CONTRACT_GRANT: NSF ATM-90-22197
CONTRACT_GRANT: NAG5-1097
Distribution Limits
Public
Copyright
Other

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