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Copyright 1992, 1995 Institute for Scientific Information, all rights reserved.
Author: OGAWA-H-S*; WU-C-Y-R; GANGOPADHYAY-P; JUDGE-D-L
Authors Abstract: N
Title: SOLAR PHOTOIONIZATION AS A LOSS MECHANISM OF NEUTRAL
INTERSTELLAR HYDROGEN IN INTERPLANETARY SPACE
Address: *UNIV SO CALIF, CTR SPACE SCI, LOS ANGELES, CA 90089
UNIV SO CALIF, DEPT PHYS & ASTRON, LOS ANGELES, CA 90089
Source: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, vol. 100,
issue A3, (MAR 1, 1995) : pp. 3455-3462.
Abstract: Two primary loss mechanisms of interstellar neutral hydrogen
in interplanetary space are resonance charge exchange ionization
with solar wind protons and photoionization by solar EUV
radiation. The Later process has often been neglected since the
average photoionization rate has been estimated to be as much as
5 to 10 times smaller than the charge exchange rate. These
factors are based on ionization rates from early measurements of
solar EUV and solar wind fluxes. Using revised solar EUV and
solar wind fluxes measured near the ecliptic plane we have
reinvestigated the ionization rates of interplanetary hydrogen.
The result of our analysis indicates that indeed the
photoionization rate during solar minimum can be smaller than
charge exchange by a factor of 5; however, during solar maximum
conditions when solar EUV fluxes are high, and solar wind fluxes
are low, photoionization can be over 60% of the charge exchange
rate at Earth orbit. To obtain an accurate estimate of the
importance of photoionization relative to charge exchange, we
have included photoionization from both the ground and
metastable states of hydrogen, We find, however, that the
photoionization from the metastable state does not contribute
significantly to the overall photoionization rate.
English Abstract: Y
Pub. Type: ARTICLE
Subject Cat: LE: GEOSCIENCES. BU: ASTRONOMY AND ASTROPHYSICS. QQ:
METEOROLOGY AND ATMOSPHERIC SCIENCES.
ISI Order #: QL214 (For ordering reprints from ISI)