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T. M. Donahue

Abstract

The implications of recent data on Venus obtained by Mariner 5, Venera 4 and ground based observations for the aeronomy of Venus is received. The theoretical thermal structure model of McElroy based on a pure CO2 atmosphere is in good agreement with the temperature deduced from the hydrogen distribution obtained by Mariner 5. No credible mechanism has been devised to recombine CO and O to CO2 in the upper atmosphere. It is suggested that O2 is formed but that CO and O2 recombine to CO2 in the dense atmosphere far enough above the cloud tops to agree with abundance measurements. Serious difficulties exist for the H2 model of the upper atmosphere. It is suggested that deuterium can account for the anomalous Lyman α glow observed by Mariner 5 without implying a large D/H planetary ratio. Other problems such as the maintenance of the ionosphere at night and the escape of water are discussed.

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T. M. Donahue

Abstract

Data obtained by the UV spectrophotometer experiments and the radio occultation experiments on Mariners 6 and 7 indicate an atomic oxygen concentration of about 3% in the upper atmosphere, an exospheric temperature of about 350K, and a very low solar EUV heating efficiency for Mars. Laboratory studies do not support mechanisms for rapid recombination of CO and O in the upper atmosphere. Transport appears to control the O concentration. However, there is still a problem of accounting for CO-O2 recombination in the lower atmosphere. A satisfactory self-consistent explanation of all of the Mariner and Venera upper atmosphere data for Mars and Venus still has not been produced. Difficulties with the presently recommended low EUV solar fluxes and high Martian airglow brightness are discussed.

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T. M. Donahue and B. Guenther

Abstract

The time and latitude variation in the radiance and altitude of the dense scattering layers observed over the summer poles is reported using OGO 6 airglow photometer data. The average altitude was 84.3 km with a tendency for higher values on the night side than on the day side of the polar cap. The average radiance increased by a factor of 5 between day 163 and day 180 (1969), but decreased thereafter.

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S. C. Liu and T. M. Donahue

Abstract

The thermal escape rate of hydrogen inferred from exospheric density measurements is too low by a factor of at least 2 to accord with the mixing ratio of H2O, H2 and CH4 observed in the stratosphere and mesosphere. The effect on the mixing ratio of adding hydrogen fluxes to support the polar wind by lateral flow and to supply a loss to charge transfer with fast protons is investigated. It is shown that these additional mechanisms can make up the deficit. The exobase hydrogen density must adjust locally to supply hydrogen to the three separate escape mechanisms at the rate demanded by the mixing ratio in the lower atmosphere and the exospheric temperature.

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S. C. Liu and T. M. Donahue

Abstract

A model for H2O, CH4, H2 and odd hydrogen is developed that properly relates the measured mixing ratios in the stratosphere to escape of H in the form of Jeans flux, charge exchange and polar wind. The resulting model predicts a temperature-dependent jeans flux in agreement with recent measurements.

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S. C. Liu and T. M. Donahue

Abstract

The distribution of hydrogen compounds between 50 km and the exobase is calculated subject to the condition that the upward flux of hydrogen atoms be sufficient to supply the thermal escape flux. The effect of varying many parameters, such as exospheric temperature, chemical rate constants, solar UV flux, and atmospheric transport coefficients is explored. It is found that H2 plays an important role in the chemistry and transport even above 100 km. It is found that the escape flux is determined mainly by the total mixing ratio and relatively insensitive to other factors at exospheric temperatures above 1000K, but is limited by the exosbase flow at lower temperatures. A thermal escape flux of 7×107 cm−2 sec−1 above 1000K is difficult to reconcile with a combine mixing ratio of H2O, H2 and CH4 greater than about 2 ppm at 50 km.

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T. M. Donahue, B. Guenther, and J. E. Blamont

Abstract

Observations with a horizon scanning airglow photometer on OGO-6 have revealed the presence of a dense scattering layer near 80 km over the geographic pole during the local summer. The layer is detected on all satellite passes above 80° latitude beginning 15 days before the solstice. The optical depth of the layer increases by more than a factor of 50 between 70° and 85°. It is suggested that noctilucent clouds are weak sporadic manifestations of these persistent polar layers.

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