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At least 1,513 records · Page 84
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NASA NTRS1976

Atmospheric rare gases in lunar rock 60015

Aliquots of lunar rock 60015 were subjected to various types of exposure and handling designed to produce terrestrial contamination, in order to test the possibility of a terrestrial origin for the terrestrial-like trapped Xe reported for lunar rock samples. Crushing the rock produced up to order-of-magnitude increases in the abundances of Ar, Kr, and Xe relative to the millimeter-sized chips of 60015 previously analyzed. Contrary to expectations for atmospheric contamination, high temperatures (above 1000 C) were necessary to remove about 75% of the trapped Kr and Xe, and the rare-gas elemental abundance ratios differed from those in terrestrial samples believed to have occluded atmospheric gases. It is concluded, on the basis of similar temperature-release profiles and elemental-fractionation patterns, that the trapped Xe observed in all these 60015 analyses is atmospheric contamination. Such a conclusion cannot unequivocally be drawn for other lunar rocks containing terrestrial-like Xe, but the present results demonstrate that arguments based on high extraction temperatures and elemental abundance ratios cannot be useful to rule out rare-gas atmospheric contamination in such samples.

Niemeyer, S.↗
NASA NTRS1977

A saturation model of the atmosphere of Uranus

A model of the atmospheric structure of Uranus is presented which differs from previous types of models in two important respects: (1) the CH4/H2 ratio is sufficiently large that CH4 is saturated to large depths in the Uranian atmosphere and (2) the internal energy flux is small compared with that due to solar heating. Because of the small internal flux, the thermal flux decreases rapidly with depth and the atmosphere is radiative to large optical depths. A CH4 droplet cloud forms where the atmosphere finally becomes convective due to the internal flux. The model is shown to be in reasonable agreement with published observations of the H2 quadrupole 3-0 and 4-0 bands, the visible (4000-6000 A) CH4 bands, and the infrared emission spectrum.

Danielson, R. E.↗
NASA NTRS1977

Planetary atmospheres with mass spectrometers carried on high-speed probes or satellites

Earth satellite-borne mass spectrometers are considered, taking into account the identification of atomic oxygen in the thermosphere with an 'open' source mass spectrometer flown on a sounding rocket, the conventional closed-source instrument, the mass spectrometers on the Atmosphere Explorer satellites, and mass spectrometer electron multiplier output. A description is presented of mass spectrometers and planetary entry probes. Attention is given to an attempt to obtain an atmospheric composition profile with a terrestrial entry probe, the descending trajectory in the early orbits of the Atmosphere Explorer C satellite, and the molecular nitrogen densities for the descending legs of the orbits. It is pointed out that chemical reactions on the surfaces of the mass spectrometer make the measurement of reactive atmospheric species such as atomic oxygen very difficult.

Nier, A. O.↗
NASA NTRS1977

Sources and sinks of atmospheric N2O and the possible ozone reduction due to industrial fixed nitrogen fertilizers

The terrestrial and marine nitrogen cycles are examined in an attempt to clarify how the atmospheric content of N2O is controlled. We review available data on the various reservoirs of fixed nitrogen, the transfer rates between the reservoirs, and estimate how the reservoir contents and transfer rates can change under man's influence. It is seen that sources, sinks and lifetime of atmospheric N2O are not understood well. Based on our limited knowledge of the stability of atmospheric N2O we conclude that future growth in the usage of industrial fixed nitrogen fertilizers could cause a 1% to 2% global ozone reduction in the next 50 years. However, centuries from now the ozone layer could be reduced by as much as 10% if soils are the major source of atmospheric N2O.

Liu, S. C.↗
NASA NTRS1978

Ozone concentration in the cabin of a Gates Learjet measured simultaneously with atmospheric ozone concentrations

A Gates Learjet Model 23 was instrumented with monitors to measure simultaneously the atmospheric and the cabin concentrations of ozone at altitudes up to 13 kilometers. Six data flights were made in February 1978. Results indicated that only a small amount of the atmospheric ozone is destroyed in the cabin pressurization system. Ozone concentrations measured in the cabin near the conditioned-air outlets were only slightly lower than the atmospheric ozone concentration. For the two cabin configurations tested, the ozone retention in the cabin was 63 and 41 percent of the atmospheric ozone concentration. Maximum cabin ozone concentration measured during these flights was 410 parts per billion by volume.

Briehl, D.↗
NASA NTRS1977

On the radiative damping of atmospheric waves

General expressions for computing time constants for radiative decay of harmonic temperature perturbations in planetary atmospheres are developed. Four spatial scales are shown to be generally important: the scale height of the atmospheric absorber, the absorption mean free path for thermal radiation, the altitude above the planetary surface, and the wavelength of the temperature perturbation. Atmospheric inhomogeneity is particularly important when the radiation mean free path and the vertical wavelength divided by 2 pi both exceed the absorber scale height. The surface is very important for wave decay at altitudes less than a few radiation mean free paths, and its effect depends on a comparison of the surface response time and the lifetime of the atmospheric perturbation. The surface response time depends on the conducting and emitting properties of the surface material and on the strength of turbulence in the planetary boundary layer. The additional influence of chemical reactions and phase changes on radiative damping is discussed, and several assumptions inherent in the development of the general expressions for time constants are evaluated. Terrestrial examples are used for purposes of illustration, but the development is kept sufficiently general so that the results remain applicable to most situations on other planets.

Prinn, R. G.↗
NASA NTRS1977

Occultation of Epsilon Geminorum by Mars. II - The structure and extinction of the Martian upper atmosphere

The occultation of Epsilon Geminorum by Mars on April 8, 1976, was observed at three wavelengths and 4-ms time resolution with the 91-cm telescope aboard NASA's G. P. Kuiper Airborne Observatory. Temperature, pressure, and number-density profiles of the Martian atmosphere were obtained for both the immersion and emersion events. Within the altitude range 50-80 km above the mean surface, the mean temperature is about 145 K, and the profiles exhibit wavelike structures with a peak-to-peak amplitude of 35 K and a vertical scale of about 20 km. The ratio of the refractivity of the atmosphere at 4500 A and 7500 A is consistent with the atmospheric composition measured by Viking 1. From the 'central flash' - a bright feature in the light curve midway between immersion and emersion - an optical depth at 4500 A of 3.3 + or - 1.7 per km atm (about 0.23 per equivalent Martian air mass) is found for the atmosphere about 25 km above the mean surface near the south polar region. This large value and its weak wavelength dependence rule out Rayleigh scattering as the principal cause of the observed extinction.

Elliot, J. L.↗
NASA NTRS1977

Photochemistry and evolution of Mars' atmosphere - A Viking perspective

Viking measurements of the upper atmosphere of Mars have indicated thermospheric temperatures below 200 K, colder than those originally calculated by remote sensing experiments. It is suggested that dynamical coupling of the upper and lower regions of the Martian atmosphere may account for the variability in thermospheric temperature. The absorption of extreme ultraviolet solar radiation may account for observed ionospheric features, and may provide a source of fast N and O atoms escaping the planet's gravitational field. Measurements of the isotopic composition of O and N may be used to place constraints on models of the evolution of the Martian atmosphere. It is suggested that previous abundance of N2 may have exceeded that of CO2 in the present atmosphere, and that large sources of H2O may exist on the planet. The present degassing rate for nitrogen is felt to be less than the time-averaged degassing rate by at least a factor of 20.

Mcelroy, M. B.↗
NASA NTRS1977

Interaction of the surfaces of the moon and Mercury with their exospheric atmospheres

A model of atmosphere-surface interactions on the moon and on Mercury is presented. This model rejects the traditional assumption that the atmospheric particle source is a 'saturated' absorbed surface layer of gas and instead assumes that interaction is with solid atoms bound in a lattice structure so that most collisions with the light atmospheric particles are free-free rather than free-bound. The energy accommodation per collision for He and H is dominated by first-order interaction terms and is generally less than 0.1 per collision. It follows that estimated thermal escape is drastically reduced for the light atoms on both bodies. Thus the model requires much reduced solar wind collection efficiencies for protons and alpha particles. Some peculiarities of the Mercury He and H atmospheres might possibly be explained by the nature of the gas-surface coupling.

Shemansky, D. E.↗
NASA NTRS1978

Effect of aerosols on the estimation of total ozone in an atmospheric column from the measurements of its ultraviolet radiance

The problem of estimating the total ozone amount of an atmospheric column in the presence of stratospheric and tropospheric aerosols is studied by means of simulated spectral measurements for the five-wavelength Nimbus 4 BUV configuration and the six-wavelength Nimbus G TOMS configuration, and by analyzing such measurements with appropriate total ozone estimation procedures. The simulated spectral measurements were generated for forty different atmospheric models arrived at by varying the total ozone content and various aerosol parameters. A total of ten different values of the solar zenith angle and eight different values of the Lambert reflectivity of the underlying surface were used. It was found that the values of total ozone in an atmospheric column estimated by the five-wavelength procedure can be in error by about + or -2% as a result of particulate contamination encountered in the terrestrial atmosphere under average conditions. Errors due to tropospheric particulate contamination can be reduced significantly by taking appropriate advantage of the additional spectral measurement offered by the Nimbus G TOMS instrument.

Dave, J. V.↗
NASA NTRS1977

Formation of the lunar helium corona and atmosphere

Helium is one of the dominant gases of the lunar atmosphere. Its presence is easily identified in data from the mass spectrometer at the Apollo 17 landing site. The major part of these data was obtained in lunar nighttime, where helium concentration reaches the maximum of its diurnal cyclic variation. The large night to day concentration ratio agrees with the basic theory of exospheric lateral transport reported by Hodges and Johnson (1968). A reasonable fraction of atmospheric helium atoms has a velocity in excess of the gravitational escape velocity. The result is a short average lifetime and a tenuous helium atmosphere. A description is presented of an investigation which shows that the atmosphere of the moon has two distinct components including low energy atoms, which are gravitationally bound in trajectories that intersect the lunar surface, and higher energy atoms, which are trapped in satellite orbits. The total helium abundance in the lunar corona is shown to be about 1.3 times 10 to the 30th power atoms.

Hodges, R. R., Jr.↗
NASA NTRS1978

Radiative transfer in spherical shell atmospheres. I - Rayleigh scattering

The plane-parallel approximation and the more realistic spherical shell approximation for the radiance reflected from a planetary atmosphere are compared and are applied to the study of a planet the size of the earth with a homogeneous conservative Rayleigh scattering atmosphere extending to a height of 100 km. Inadequacies of the approximations are considered. Radiance versus height distributions for both single and multiple scattering are presented, as are results for the fractional radiance from altitudes in the atmosphere which contribute to the total unidirectional reflected radiance at the top of the atmosphere. The data can be used for remote sensing applications and planetary spectroscopy.

Adams, C. N.↗
NASA NTRS1979

Solar wind sputtering effects in the Martian atmosphere

A Monte Carlo simulation of the sputtering of the upper atmosphere of Mars by the solar wind was performed. The calculated sputtering yields imply loss rates (molecules/cm square - sec escaping the planet) for carbon dioxide, carbon, and oxygen of R(CO2) = 2.6 X 1000000/cm square - sec, R(C) = 6.6 X 1000000/cm square - sec, and R(O) = 7.7 X 1000000/cm - sec. The total mass loss by sputtering is only about 10% of that due to chemical and photo-chemical processes, but sputtering provides a major exospheric sink for carbon. The erosion process described here preferentially removes the lighter components of the atmosphere. Calculations based on a Monte Carlo simulation suggest that for a model atmosphere, 97% of the N2 and 33% of the CO2 originally present may have been sputtered away over 4.5 X 10 to the 9th power y. In the same length of time the (15)N/(14)N isotopic ratio for the bulk atmosphere would have increased by a factor 1.7.

Watson, C. C.↗
NASA NTRS1978

Saturn's microwave spectrum: Implications for the atmosphere and the rings

Measurements of Saturn's disk temperature are compiled to determine the planet's microwave spectrum from 1 mm to 100 cm wavelength. The data were adjusted to conform with a common flux density scale. A model of Saturn's rings is used to remove the effects of the rings from the atmospheric component at centimeter and decimeter wavelengths. Theoretical spectra for a number of convective atmospheric models were computed and compared with the observed spectrum. Radiative-convective models with approximately solar composition and with an effective temperature of approximately 89 K are in good agreement with the observations. The agreement between the observed and theoretical spectra is a strong indication that gaseous ammonia is present in Saturn's atmosphere. A good fit to the data is obtained with an ammonia mixing ratio of approximately 5 x 10,0001. A comparison of the millimeter wavelength data with the best-fitting atmospheric spectrum indicates that the thermal component of the ring brightness temperature near 1 mm wavelength is approximately 25 k.

Klein, M. J.↗
NASA NTRS1978

Transport properties in the atmosphere of Jupiter

The calculation of transport properties near the surface of a probe entering the atmosphere of Jupiter is discussed for (1) transport properties in the pure Jovian atmosphere, (2) transport properties for collisions between monatomic carbon atoms, including the effect of excited electronic states, (3) transport properties at the boundaries for mixing of the pure Jovian atmosphere and the atmosphere due to the injection of gaseous ablation products, and (4) transport properties for interactions involving some of the molecular ablation products. The transport properties were calculated using the kinetic theory of gases. Transport collision integrals were calculated for only a limited set of empirical and semiempirical interaction potentials. Since the accuracy of the fit of these empirical potentials to the true potential usually determines the accuracy of the calculation of the transport properties, the various interaction potentials used in these calculations are discussed.

Biolsi, L., Jr.↗
NASA NTRS1979

A GCM simulation of the earth-atmosphere radiation balance for winter and summer

The radiation balance of the earth-atmosphere system simulated by using the general circulation model (GCM) of the Laboratory for Atmospheric Sciences (GLAS) is examined in regards to its graphical distribution, zonally-averaged distribution, and global mean. Most of the main features of the radiation balance at the top of the atmosphere are reasonably simulated, with some differences in the detailed structure of the patterns and intensities for both summer and winter in comparison with values as derived from Nimbus and NOAA (National Oceanic and Atmospheric Administration) satellite observations. Both the capability and defects of the model are discussed.

Wu, M. L. C.↗
NASA NTRS1979

Studies in upper and lower atmosphere coupling

The theoretical and data-analytic work on upper and lower atmosphere coupling performed under a NASA Headquarters contract during the period April 1978 to March 1979 are summarized. As such, this report is primarily devoted to an overview of various studies published and to be published under this contract. Individual study reports are collected as exhibits. Work performed under the subject contract are in the following four areas of upper-lower atmosphere coupling: (1) Magnetosphere-ionosphere electrodynamic coupling in the aurora; (2) Troposphere-thermosphere coupling; (3) Ionosphere-neutral-atmosphere coupling; and (4) Planetary wave dynamics in the middle atmosphere.

Chiu, Y. T.↗
NASA NTRS1979

Energy transport through the solar atmosphere

The energy transport through the solar atmosphere and the source of energy which heats the chromosphere and the solar corona are studied. Wave propagation in the solar atmosphere and in the heating of the solar atmosphere is discussed as a source and transport medium. The source of the waves is thought to be the photospheric short period oscillations. Simultaneous observations from the photosphere to the corona at the solar disk center are reported. Emphasis is on the possible association of aperiodic brightenings high in the atmosphere with specific events in the photosphere.

Harvey, K. L.↗