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  • 1
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    Analysis of Pioneer Venus Orbiter ultraviolet spectrometer Lyman alpha data from near the subsolar region (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Pioneer Venus Orbiter ultraviolet spectrometer data from 20 orbits which span 3 years have been analyzed to determine the atomic hydrogen number density and vertical flux at the exobase as a function of solar zenith angle, F(10.7) index, and spacecraft latitude. From 1979 through 1981, the exobase number density n(c) and flux phi(c) are remarkably constant at n(c) = 6.0 + or - 1.5 x 10 to the 4th/cu cm and phi(e) = 7.5 + or - 1.5 x 10 to the 7th/sq cm per s in the subsolar region. The integrated vertical column density above 110 km is 3.6 + or - 1 x 10 to the 13th/sq cm. An empirical relationship is determined between the line center solar flux at H Lyman alpha, piF(0), and the F(10.7) index.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 1766-177
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  • 2
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    Atomic hydrogen on Mars - Measurements at solar minimum (1978)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: The Copernicus Orbiting Astronomical Observatory was used to obtain measurements of Mars Lyman-alpha (1215.671-angstrom) emission at the solar minimum, which has resulted in the first information on atomic hydrogen concentrations in the upper atmosphere of Mars at the solar minimum. The Copernicus measurements, coupled with the Viking in situ measurements of the temperature (170 plus or minus 30 K) of the upper atmosphere of Mars, indicate that the atomic hydrogen number density at the exobase of Mars (250 kilometers) is about 60 times greater than that deduced from Mariner 6 and 7 Lyman-alpha measurements obtained during a period of high solar activity. The Copernicus results are consistent with Hunten's hypothesis of the diffusion-limited escape of atomic hydrogen from Mars.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 200; June 2
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  • 3
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    The UV dayglow 3, OI emissions at 989, 1027, 1152, 1304, and 1356A (1980)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Rocket observations of the dayglow spectrum between 530 and 1500A were obtained on 9 January 1978 at a solar zenith angle of 56 deg. Data were obtained from 80 to 260 km with viewing angles of 40, 90, and 180 deg to the local zenith. OI emissions were observed at 989, 1027, 1152, 1304, and 1356A. Analysis of these data with a radiative transfer model using the energy dependences of currently accepted excitation cross sections, branching ratios and photoelectron fluxes shows that electron impact excitation is the primary source of these emissions. The infrared emission rates at 7990 and 11287A are also calculated in this analysis for comparison with previous observations and estimates.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters; 7; Dec. 198
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  • 4
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    The ultraviolet dayglow. IV - The spectrum and excitation of singly ionized oxygen (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The emission line spectrum of singly ionized atomic oxygen (O II) dominates the day airglow spectrum in the extreme ultraviolet below 834 A. The strongest resonance line, at 834 A, is optically thick and an analysis of height profiles obtained from rocket observations between 140 and 265 km in specific viewing directions indicates that the principal excitation source is direct photoionization of neutral atomic oxygen. Strong emission at 538-539 A is most likely due to the quartet rather than the doublet transitions, which both occur at these wavelengths and which are not spectrally resolved in the data. The intensities of the weaker lines are consistent with recent laboratory measurements of transition branching ratios. Several strong O II lines near He I 584 produce severe contamination of low-altitude (less than 400 km) measurements of geocoronal helium emission made with thin-film broadband photometers.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 86; May 1
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  • 5
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    The UV dayglow 2, Ly-alpha and Ly-beta emissions and the H distribution in the mesosphere and thermosphere (1980)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Rocket observations of the Lyman alpha and Lyman beta day airglow are analyzed using a nonisothermal spherical model of the radiation field. This new model provides, for the first time, a method of determining atomic hydrogen densities in the mesosphere and thermosphere. Interpretation of Lyman alpha data taken between 80 and 260 km is consistent with current mesospheric and thermospheric models, with H density equal to 1.9 x 10 to the 7th/cu cm at 100 km. Analysis of 1025 A data suggests that the emission is dominated by Lyman beta with perhaps as much as a 30% contribution from OI 1027.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters; 7; July 198
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  • 6
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    The ultraviolet dayglow at solar maximum. III - Photoelectron-excited emissions of N2 and O (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Rocket observations of the far ultraviolet dayglow spectrum near solar cycle maximum are analyzed using laboratory cross sections, atmospheric composition models, and photoelectron production models. Photoelectron-excited emissions of N2 and O are used to derive a self-consistent description of the atmosphere at solar maximum. Spectral synthesis of the N2 Lyman-Birge-Hopfield bands shows a departure of a 1Pi(q) state vibrational populations from the direct excitation theory. Observations of the N2 second positive (0, 0) 3371-A band and O I 1356-A emission indicate an exospheric temperature of 1600 K, 200 K higher than predicted by empirical models. The empirical models are also found to overestimate the O and O2 densities required to fit the data by a factor of 2 and 1.4, respectively. These results are compared to the results of an analysis of similar observations made in 1978 near solar minimum.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 6608-661
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  • 7
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    Global atomic hydrogen density derived from OGO-6 Lyman-alpha measurements (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The paper analyzes a one-year set of Lyman-alpha airglow data measured in the local zenith at altitudes from 400 to 1100 km by a UV photometer aboard OGO-6. The zenith-intensity data are fitted to theoretical airglow calculations in four spherically symmetric models of the hydrogen geocorona to determine both the Ly-alpha solar flux at line center and the average atomic hydrogen column density. After correcting for a loss of instrument sensitivity, the Ly-alpha flux is found to be linearly correlated with daily Zurich sunspot number. It is also found that the hydrogen density is inversely correlated with Jacchia exospheric temperature, but the dependence is not that predicted by steady-state models with Jeans evaporative escape as the only loss mechanism. It is suggested that charge-exchange production of fast hydrogen atoms from 'hot' ionospheric protons might provide the additional loss this result requires.
    Keywords: GEOPHYSICS
    Type: Planetary and Space Science; 24; Apr. 197
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  • 8
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    Mariner 6, 7, and 9 ultraviolet spectrometer experiment - Analysis of hydrogen Lyman alpha data (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Four Lyman alpha airglow measurements of the limb and disk of Mars, made by ultraviolet spectrometers on Mariner 6 and 7 in 1969 and Mariner 9 in 1971, are analyzed to determine the amount and distribution of atomic hydrogen above 80 km. The variation of atomic hydrogen with altitude is calculated by using time-independent chemical diffusion models from 80 to 250 km, and an exospheric model is used above 250 km. By employing radiative transfer theory that includes effects of pure absorption and accounts for temperature variations in the atmosphere, a spherical model of the airglow Lyman alpha emission is used to produce theoretical intensities for comparison with the data. It is found that (1) the exospheric temperature and distribution in 1971 are consistent with those determined in 1969, (2) the vertical optical depth above 80 km was 2.2 in 1969 and 5 in 1971, and (3) the derived atomic hydrogen distribution from 80 to 250 km requires a source of atomic hydrogen above 80 km. Comparison of observed profiles with chemical diffusion models implies a large downward flow of atomic hydrogen at 80 km coupled with a large upward flow of molecular hydrogen.-
    Keywords: SPACE RADIATION
    Type: Journal of Geophysical Research; 79; Apr. 1
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  • 9
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    The Mariner 5 ultraviolet photometer experiment - Analysis of Rayleigh-scattered and 1304-A radiation from Venus (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Airglow measurements of the disk of Venus, made by the ultraviolet photometer on Mariner 5 on October 19, 1967, are analyzed to determine the sources of the observed emission. Rayleigh-scattering models for a semi-infinite atmosphere are used to determine the scale height and single-scattering albedo of the scatterer and to determine the 1304-A emission rate. It is found that (1) the scale height of the Rayleigh-scattered radiation is about 4.5 km, (2) the single-scattering albedo near 2000 A is about 0.8, and (3) 500 R of 1304-A radiation is detected at solar zenith angles between 90 and 95 deg.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 80; Aug. 1
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  • 10
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    Mariner 6 and 7 ultraviolet spectrometer experiment - Analysis of hydrogen Lyman- alpha data (1971)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Atomic hydrogen dayglow Lyman alpha structure of Mars exosphere from Mariner 6 and 7 UV spectrometric observations
    Keywords: SPACE SCIENCES
    Type: ; 331-335. (
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