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Author: Ogawa, H.S.; Phillips, E.; Judge, D.L.
Title: Direct measurements of the helium photoionization rate from sounding rockets
Source: Journal of Geophysical Research (June 1, 1997), vol.102, no.A6 p. 11557-66
Abstract: A method of directly measuring the absolute helium photoionization rate coefficient independent of
detailed solar EUV spectra and photoionization cross sections has been demonstrated. Three such
measurements were obtained using windowless rare-gas ionization cells operated in an optically
thin mode. The cells were launched on Nike/Terrier boosted Black Brant sounding rockets from the
White Sands Missile Range in 1983, 1989, and 1990. The rate coefficients were determined for
altitudes from 150 to 330 km and were extrapolated to give values of 11.1*10/sup -8/ s/sup
-1/+or-11%, 21.3*10/sup -8/ s/sup -1/+or-16%, and 13.2*10/sup -8/ s/sup -1/ 11% at the "top" of
the Earth's atmosphere. The solar activity levels were characterized by absolute F/sub 10.7/ values
of 119, 172 and 142 (10/sup -22/ W m/sup -2/ Hz/sup -1/), respectively. The top of the atmosphere
solar EUV flux values inferred from the measured ionization rates were found to be consistent with
absolute flux measurements obtained simultaneously with a neon ionization cell operated in the
optically thick mode.
Pub. Type: Journal Paper