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Donahue, T. M.

Publications and source records attributed to Donahue, T. M..

At least 73 records · Page 4
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NASA NTRS1976

Ultraviolet absorption experiment MA-059

The ultraviolet absorption experiment performed during the Apollo Soyuz mission involved sending a beam of atomic oxygen and atomic nitrogen resonance radiation, strong unabsorbable oxygen and nitrogen radiation, and visual radiation, all filling the same 3 deg-wide field of view from the Apollo to the Soyuz. The radiation struck a retroreflector array on the Soyuz and was returned to a spectrometer onboard the Apollo. The density of atomic oxygen and atomic nitrogen between the two spacecraft was measured by observing the amount of resonance radiation absorbed when the line joining Apollo and Soyuz was perpendicular to their velocity with respect to the ambient atmosphere. Information concerning oxygen densities was also obtained by observation of resonantly fluorescent light. The absorption experiments for atomic oxygen and atomic nitrogen were successfully performed at a range of 500 meters, and abundant resonance fluorescence data were obtained.

Donahue, T. M.↗
NASA NTRS1976

Effect of odd hydrogen on ozone depletion by chlorine reactions

The present paper discusses how the shape of the ozone layer changes under the influence of injected ClX for several choices of two key HOx reaction rates. The two HOx reactions are: OH + HO2 yields H2O + O2 and O + HO2 yields OH + O2. Results of calculations are presented which show that the two reaction rates determine the stratospheric concentrations of OH and HO2, and that these concentrations regulate the amount by which the stratospheric ozone column can be reduced due to injections of odd chlorine. It is concluded that the amount of ozone reduction by a given mixing ratio of ClX will remain very uncertain until the significance of several possible feedback effects involving HOx in a chlorine-polluted atmosphere are determined and measurements of the reaction rates and HOx concentrations are made at the relevant temperatures.

Donahue, T. M.↗
NASA NTRS1976

The O(3P) and N(4S) density measurement at 225 km by ultraviolet absorption and fluorescence in the Apollo-Soyuz test project

The densities of O(3P) and N(4S) at 225 km were determined during the Apollo Soyuz Test Project by a resonance absorption/fluorescence technique in which OI and NI line radiation produced and collimated on board the Apollo was reflected from the Soyuz back to the Apollo for spectral analysis. The two spacecraft maneuvered so that a range of observation angles of plus or minus 15 deg with respect to the normal to the orbital velocity vector was scanned. The measurements were made at night on two consecutive orbits at spacecraft separations of 150 and 500 m. The resulting relative counting rates as function of observation angle were compared to calculated values to determine the oxygen value. This value agrees with mass spectrometric measurements made under similar conditions. The nitrogen value is in good agreement with other measurements and suggests a smaller diurnal variation than is predicted by present models.

Kaufman, F.↗
NASA NTRS1976

Model ionospheres of Jupiter

The principal concepts presently involved in modeling the Jovian ionosphere are reviewed. A model ionosphere is developed on the basis of our present knowledge of atmospheric composition, relevant chemical and ion-molecule reactions, with their associated rate constants. The shortcomings of this model are discussed when it is compared with the electron density profile obtained from the Pioneer 10 radio occultation data. It is demonstrated that the apparent great extent of the observed topside ionosphere may imply a hot thermosphere, as if Jupiter sustained a corona. Some of the layers observed in the electron density profile may be due to sporadic-E like clustering of protons and other ions.

Atreya, S. K.↗
NASA NTRS1975

The temperature gradient between 100 and 120 km

Oxygen density profiles inferred from Ogo 6 green nightglow emission vary too sharply between 100 and 120 km to be consistent with temperature gradients in standard model atmospheres, and the eddy diffusion coefficient K determined from these observations reaches its maximum below 115 km. For three atomic oxygen profiles obtained at geographic latitudes of -27.69, +48.89, and +59.10 the temperature profiles required to create a downward flux that varies with altitude as the integrated photolytic production rate above that altitude are calculated, assuming K to be invariant with altitude and latitude. The oxygen distribution can be reconciled with a constant eddy coefficient above 100 km if the temperature gradient reaches a value between 10 and 20 deg K/km for low values of the eddy coefficient (about 500,000 sq cm/sec) or between 30 and 50 deg K/km for a higher eddy coefficient (about 1.6 million sq cm/sec). The maximum gradient for the Jacchia (1971) model is about 10 deg K/km. These temperature profiles predict Ar/N ratios consistent with those measured by sounding rockets. The low K profiles are large enough to remove a large part of the solar energy deposited below 120 km by thermal conduction.

Donahue, T. M.↗
NASA NTRS1975

A model of the Venus ionosphere

Results of model calculations of the Venus ionosphere from 120 to 300 km are presented. The chemical scheme and reaction rates used are the same as given by Kumar and Hunten (1974) except that the electron temperature dependence of the dissociative recombination rates is taken into account. Calculations are made for low and high atomic oxygen models in which the O/CO2 ratios are 0.4% and 4% respectively at 140 km, and the results agree well in shape and magnitude with the Mariner 5 and 10 occultation results in the chemically controlled region. Reasonable agreement is obtained at higher altitudes if diffusive equilibrium and high vertical flow velocities (10 km/s) are assumed as upper boundaries for the Mariner 5 and 10 conditions respectively, although solar wind-ionosphere interactions are considered to be the controlling mechanism for the Mariner 10 results.

Nagy, A. F.↗
NASA NTRS1975

The aeronomy of the upper atmosphere of Venus

It is shown that rather tight constraints can be placed on the mixing ratio of atomic oxygen in the upper atmosphere of Venus, as well as that of CO and molecular oxygen, unless extraordinary processes which lead to a very large efflux of hydrogen from the planet are postulated. The analysis conducted is similar to the investigation carried out for the earth by Liu and Donahue (1974). If Jeans escape provides the main escape mode for hydrogen from Venus, the concentration ratio of atomic oxygen to carbon dioxide at 130 km is much less than 1% and some mechanism other than resonance scattering plus photoelectron excitation must account for the oxygen airglow.

Liu, S. C.↗
NASA NTRS1975

OGO-6 observations of 5577 A

A brief review is given of the data obtained by the horizon-scanning 5577-A airglow photometer flown aboard OGO 6. Data are presented which show the contributions to the 5577-A emission from the F-1 region and the Chapman airglow layer. Emission rates are calculated for both regions on the basis of the dissociative-recombination and Chapman reactions, and the atomic oxygen density and downward flux are inferred from the emission rates and several assumptions concerning the temperature dependence of the rate constants. Latitude variations in the emission rates are discussed along with variations in the altitude of the 5577-A airglow. It is shown that there is a large semiannual variation in the average effective transport properties of the lower thermosphere, that the atomic oxygen profiles near 110 km suggest a maximum in eddy diffusion at about that altitude, and that systematic variations in the altitude of the atomic oxygen maximum probably do not exceed 2 km.

Donahue, T. M.↗
NASA NTRS1974

An upper limit to the product of NO and O densities from 105 to 120 km

From the Ogo 6 horizon-scanning-photometer data a useful upper limit can be set to the radiance of nightglow in the O-NO afterglow continuum above 105 km. The upper limit is a factor of about 5 less than the product of observed NO densities and Jacchia (1971) O model densities.

Donahue, T. M.↗
NASA NTRS1974

Outer planets Grand Tour ultraviolet spectroscopy experiment

The principal objective is presented of the UV observations, with emphasis placed on hydrogen and helium. Calculations are given for airglow and occultation. Mission requirements and trajectories are also reported for future observations.

Donahue, T. M.↗
NASA NTRS1974

Spatial and temporal behavior of atomic oxygen determined by Ogo 6 airglow observations

Maps are produced of the atomic oxygen density near 97 km showing a strong variation in latitude, longitude, universal time, and time of year. These densities are deduced from atomic oxygen green nightglow observations carried out from Ogo 6. Meridional wind patterns needed to support the asymmetries observed in local oxygen production and loss rates are deduced.

Donahue, T. M.↗
NASA NTRS1974

Jupiter's ionosphere - Prospects for Pioneer 10

Model Jovian ionospheres are constructed for comparison with Pioneer 10 results. Electron density maxima are predicted at a level approximately 220 kilometers above an assumed reference height where the hydrogen density is 10 to the 16-th power molecules per cubic centimeter. It may be possible to use observations of the electron density to locate the turbopause. Attention is drawn to a possible strong source of ionized sodium from Io which might lead to large electron densities at low altitudes.

Atreya, S. K.↗
NASA NTRS1973

A search for far-ultraviolet emissions from the lunar atmosphere

An ultraviolet spectrometer aboard the Apollo 17 orbiting spacecraft attempted to measure ultraviolet emissions from the lunar atmosphere. The only emissions observed were from a transient atmosphere introduced by the lunar landing engine. The absence of atomic hydrogen implies that solar wind protons are converted to hydrogen molecules at the lunar surface.

Fastie, W. G.↗
NASA NTRS1973

Distribution of atomic oxygen in the upper atmosphere deduced from Ogo 6 airglow observations.

The atomic oxygen distribution as a function of altitude between 80 and 120 km and as a function of latitude has been deduced from Ogo 6 557.7-nm airglow photometer data obtained between August 1969 and April 1970. The results indicate that the density ranges from 15 to 50 billion per cu cm at 120 km; that there is a semiannual variation by a factor of 3 in the global average density near 100 km in phase with the satellite drag semiannual effect; and that large latitudinal variations occur with maximums between 40 and 60 deg in the winter hemisphere and sometimes deep minimums in the tropics. The implication of these results for meridional and vertical transport patterns is discussed.

Donahue, T. M.↗
NASA NTRS1973

The altitude of the scattering layer near the mesopause over the summer poles.

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.

Donahue, T. M.↗
NASA NTRS1973

Ultraviolet spectrometer experiment

The ultraviolet spectrometer (UVS) onboard the Apollo 17 orbiting spacecraft was used to measure emissions from the lunar atmosphere. The UVS and calibration are discussed along with the lunar atmosphere observations and lunar albedo measurements.

Fastie, W. G.↗
NASA NTRS1972

The altitude of the scattering layer near the mesopause over the summer poles

The variation in radiance and altitude with time and latitude is reported for the dense scattering layers observed over the summer poles by the OGO 6 airglow photometer. 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.

Donahue, T. M.↗