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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Global atomic oxygen density derived from OGO-6 1304 A airglow measurements

Results are presented for analysis of data on the atomic oxygen 1304-A triplet in the earth's dayglow between 400 and 1100 km which were obtained with the OGO-6 UV photometer during a 40-day period that included both quiet and disturbed conditions. Variations in the atomic oxygen column density are analyzed by obtaining best-fit models in which the 1304-A emission is produced by solar resonance scattering and photoelectron excitation. It is shown that the column density can be determined uniquely from the measured 1304-A intensity, provided the excitation processes can be described quantitatively. The values of the excitation parameters are determined directly from the data, and the deduced variations in column density over the daytime atmosphere are found to agree well with the Jacchia (1971) models. The latitudinal dependence of the column-density variations during a geomagnetic storm are discussed, the results are compared with recent measurements of the solar 1304-A fluxes as well as with calculations of the photoelectron excitation, and a method is suggested for determining the absolute atomic oxygen densities.

Strickland, D. J.↗
NASA NTRS1976

The O I /5577-A wavelength/ airglow - Observations and excitation mechanisms

Analysis of the O I /5577-A wavelength/ airglow observations conducted on board the Atmosphere Explorer C satellite yields the following results when combined with simultaneous measurements of ion and neutral composition. A volume emission rate profile derived after sunset requires the production of an O(1S) atom in 8% of the O2(+) recombinations. Photoelectric impact on atomic oxygen and the dissociative recombination of O2(+) are important sources of O(1S) in the dayglow; however, the airglow measurements require a large additional production of O(1S) below 200 km in addition to these. The reaction N + O2(+) yielding NO(+) + O(1S) can provide the missing O(1S) source if the rate coefficient is near 2.5 times 10 to the minus 11th cu cm per sec.

Frederick, J. E.↗
NASA NTRS1978

The ionosphere and airglow of Venus - Prospects for Pioneer Venus

The paper presents model calculations for the Cytherean nighttime and daytime ionosphere. It is shown how some of the proposed mechanisms can be tested with the aid of the Pioneer Venus observations scheduled for December 1978. Theoretical calculations of the energetics of the Cytherean ionosphere are performed, and it is concluded that the Project Venus measurements will find elevated ion and electron temperatures, resulting primarily from energy fluxes associated in some manner with the solar wind. According to this model, the energy flux will act directly on the ion gas. Ultraviolet dayglow intensities were calculated, and it is anticipated that hundreds of kR's of CO2-related emission features such as the CO Cameron bands will be observed. Nightside ionosphere calculations were made assuming the precipitation of energetic electrons as an ionization source, and the intensities of some of the resulting emission features are calculated.

Cravens, T. E.↗
NASA NTRS1979

O2/1 Delta/ emission in the day and night airglow of Venus

An intense airglow from O2(1 Delta) at 1.27 microns on both the light and the dark sides of Venus has been detected by using a ground-based high-resolution Fourier-transform spectrometer. Both dayglow and nightglow are roughly 1,000 times brighter than the visible O2 nightglow found by Veneras 9 and 10 in 1975. The column emission rate of O2(1 Delta) from Venus is close to the rate at which fresh O atoms are produced from photolysis of CO2 on the day side. Formation of O2(1 Delta) is thus a major step in the removal of O atoms from the atmosphere, and dynamical processes must carry these atoms to the night side fast enough to yield a maximum density near 90 km, which is almost constant over the planet.

Connes, P.↗
NASA NTRS1981

Extreme ultraviolet observations from Voyager 1 encounter with Saturn

Hydrogen Lyman-alpha, helium and molecular hydrogen band ultraviolet emissions from Saturn and the Titan atmosphere are considered. The Saturn H2 band excitation mechanism, while qualitatively similar to that of Jupiter, is closely related to the solar flux. The occurrence of auroras at 80 deg latitude suggests an earth-like magnetotail activity. No ion emissions have been detected from the Saturn magnetosphere. Although nitrogen emissions excited by particles have been detected in the Titan dayglow and bright limb scans, no such emission has been detected from its dark atmosphere. Enhancement of the nitrogen emission is observed in the region of interaction between Saturn's corotating plasmasphere and the Titan atmosphere.

Broadfoot, A. L.↗
NASA NTRS1982

The ultraviolet spectrum of an aurora 530-1520 A

Ultraviolet spectra between 530 and 1520 A of an active auroral arc were obtained at 6.5-A instrumental resolution. Several new emission features are identified, including several bands of the N2 Birge-Hopfield (1, v-double-prime) progression and numerous N I multiplets, the latter being preponderant at low altitudes. The improved instrumental resolution over previous experiments in the wavelength region below 1200 A allows for a partial resolution of the complex structure between 900 and 1100 A reported in earlier work. The ratio of O I 1356 to N2 Lyman-Birge-Hopfield is smaller than in the dayglow at a similar altitude, and this is interpreted as evidence for a depletion of atomic oxygen in the auroral ionosphere relative to mid-latitude composition.

Feldman, P. D.↗
NASA NTRS1982

Radiative transfer with partial frequency redistribution in inhomogeneous atmospheres - Application to the Jovian aurora

A direct finite difference numerical solution for the equation of radiative transfer by the Feautrier method is developed for use in planetary atmospheres. The procedure described here uses a plane-parallel atmosphere, and can treat partial frequency redistribution, inhomogeneity, external or internal sources, and various boundary conditions. Isotropic scattering is assumed, but in the case of no frequency redistribution, Rayleigh scattering can also be handled. A program utilizing this method is tested in a variety of situations against more powerful and elaborate methods. The case of the Lyman alpha aurora on Jupiter is then considered, where the effects of partial frequency redistribution are shown to be of great importance. New results for the detailed line profiles for Lyman alpha in the Jovian aurora are presented. The method is quite versatile, and should be especially useful in studying a wide range of problems related to auroral or dayglow emissions in planetary atmospheres.

Gladstone, G. R.↗
NASA NTRS1982

Eddy mixing coefficient on Saturn

Data on the composition, thermal structure, and Lyman-alpha dayglow of Saturn, when analyzed in conjunction with photochemical models of the hydrocarbons and the atomic hydrogen production, yield the homopause value of the eddy diffusion coefficient to be approximately 100 million/sq cm per sec. The equatorial value of the eddy diffusion coefficient at the homopause of Saturn is thus found to be approximately 100 times greater than on Jupiter. The mesosphere (and presumably, troposphere) of Saturn appears to be considerably more turbulent than the upper atmosphere of Jupiter.

Atreya, S. K.↗
NASA NTRS1982

Spectroscopic imaging of the thermosphere from the Space Shuttle

The design features, performance characteristics, and intended missions for the Imaging Spectrometric Observatory scheduled to fly on the first Spacelab Shuttle mission in 1983 are described. The instrument comprises an array of five imaging spectrometers covering the spectral range 300-1200 A. The spectrometers operate simultaneously, using CCDs as collector elements. Resolution on the first flight will be limited to 3 A, with coverage to containing the dynamic range from nocturnal signals to the bright earth. A minicomputer in the Spacelab will permit crewmember interaction with the measurements, while data will be telemetered in real-time to a ground station. Initial mission objectives include observations of dayglow, nightglow, and twilightglow over the full wavelength range capability.

Torr, M. R.↗
NASA NTRS1983

An analysis of the reflection spectrum of Jupiter from 1500 A to 1740 A

The Jovian reflection spectrum was modeled to determine the mixing ratios of C2H2, the upper limits to mixing ratios of C2H4, C4H2, and NH3, to detect the amount of dust in the stratosphere, and to measure the intensity of the H2 Lyman band dayglow emission. Data were gathered by the IUE spacecraft in the wavelength regions 1500 A to 1740 A, concentrating in the 10 mbar pressure region. Detailed Jupiter model parameters are provided. The mixing ratios of C2H2, C2H6, and C4H2 were found to be near 10 to the -7th, 6.6 x 10 to the -6th, and 2.9 x 10 to the -10th, respectively. Comparisons made with the Voyager 1 and 2 data indicated that the scale height of C2H2 in the 150-10 mbar region is double that of the bulk atmosphere. The data are significant for photochemical modeling of the upper Jovian atmosphere.

Gladstone, G. R.↗
NASA NTRS1984

Twilight Intensity Variation of the Infrared Hydroxyl Airglow

The vibration rotation bands of the hydroxyl radical are the strongest features in the night airglow and are exceeded in intensity in the dayglow only by the infrared atmospheric bands of oxygen. The variation of intensity during evening twilight is discussed. Using a ground-based Fourier Transform Spectrometer (FTS), hydroxyl intensity measurements as early as 3 deg solar depression were made. Models of the twilight behavior show that this should be sufficient to provide measurement of the main portion of the twilight intensity change. The instrument was equipped with a liquid nitrogen-cooled germanium detector whose high sensitivity combined with the efficiency of the FTS technique permits spectra of the region 1.1 to 1.6 microns at high signal-to-noise to be obtained in two minutes. The use of a polarizer at the entrance aperture of the instrument reduces the intensity of scattered sunlight by a factor of at least ten for zenith observations.

Lowe, R. P.↗
NASA NTRS1986

Comment on the paper 'On the influx of small comets into the earth's upper atmosphere. II - Interpretation'

Frank et al. (1986) argue that, on the basis of dayglow observations, about 20 small comets of mass roughly 100,000 g hit the earth each minute. The proposed comets appear to require dust mantles; for otherwise they would evaporate quickly and contribute to the solar wind. Such an enrichment is not observed. An order-of-magnitude argument based on comet sizes, densities, and meteoritic dust influx is used here to show that the dust mantles can have a maximum thickness of about 200 microns. A reasonable estimate gives a thickness of about 0.2 micron. The mantles are thus too thin to suppress evaporation.

Frank, L. A.↗
NASA NTRS1986

Comment on the paper 'On the influx of small comets into the earth's upper atmosphere. I - Observations'

The observations of transient decreases or holes in the EUV dayglow reported by Frank et al. (1986) and attributed to an influx of small comets into the earth atmosphere are discussed critically. The techniques used in acquiring and analyzing the observational data are examined, and it is argued that the decreases are probably instrument artifacts. A critique of the geophysical basis of the comet hypothesis is also included. In a reply by Frank et al., the instrument-artifact argument is rejected, in part on the basis of the statistical properties of the holes observed. Additional observational data are presented in graphs and dynamics Explorer 1 images are analyzed in detail.

Chubb, T. A.↗
NASA NTRS1986

The vibrational distribution of O2(+) in the dayside ionosphere

The vibrational distributions of O2(+) in the X2Pi(g), A2Pi(u), a4Pi(u), and b4Sigma(-)g states in the dayside terrestrial ionosphere are calculated for both low and high solar activity models. The distributions are found to be significantly different from the O2(+) vibrational distributions found by Fox (1985) for the Venusian ionosphere. The sources and sinks of vibrational excitation and the implications for the chemistry, dayglow, and hot oxygen coronas are discussed. Finally, intensities of the first negative and second negative band systems of O2(+) are presented.

Fox, J. L.↗
NASA NTRS1987

Comment on the paper 'On the influx of small comets into the earth's upper atmosphere'

The possibility that comets containing up to 100 tons of ice encounter the earth's atmosphere at a rate of one every 20 min is discussed. Cometary 'hail storms' were proposed to explain observed regular transient decreases in the atmospheric UV dayglow intensity. The decreases take the form of dark 'holes' up to 50 km across. The probability that clouds of objects assumed to be as dark as the nucleus of Comet Halley between the earth and moon would be detectable by ground-based electrooptical deep space telescopes is considered. Conflicting projections of the number of objects which would be detected per hour are examined. High correlations are noted between cometary passages (Comets Encke, Tuttle, Tempel) and intervals of meteor showers (Taurids, Leonids, Geminis, etc.). The holes, however, are not correlated or coincident with the showers. It is suggested that dedicated searches for the unclassified dark objects be carried out in November, when cometary fluxes are high.

Soter, Steven↗
NASA NTRS1987

Comment on the papers 'On the influx of small comets into the earth's upper atmosphere. I - Observations and II - Interpretation'

The Generic Screening Object hypothesis of Frank et al. (1986) is refuted, and it is indicated that the DE-1 dark pixel events do not serve as evidence for a large cometary influx. It is shown that the average scan line count profiles of the dark pixel events show no significant reductions in the two neighboring pixel positions, although at least a 9 percent reduction would be expected if the dark pixels were the result of shielding of the photometric field of view. In a reply, Frank et al. uphold their previous hypothesis, pointing out that the suggestion that the atmospheric holes are not a geophysical phenomenon is incorrect due to: (1) the use of an overly simplified model for the instrument responses to small, opaque objects as seen against a statistically fluctuating screen of dayglow intensities; and (2) an insufficient treatment of the observations.

Cragin, B. L.↗
NASA NTRS1988

Remote sensing of atmospheric oxygen from a sounding rocket

This paper describes a rocket experiment to investigate mechanisms governing the interactions between two of the fundamental components of the solar-terrestrial system: the solar ionizing radiation and the earth's upper atmosphere. The aim is to characterize the extreme ultraviolet (EUV) emissions resulting from these interactions in terms of physical parameters so that EUV remote sensing can be gainfully employed as a quantitative diagnostic of the terrestrial atmosphere and plasma environment. The payload consists of a high-resolution (about 0.5 A) spectrometer to measure the EUV emissions (980-1360 A) of the earth's dayglow, a moderate resolution (about 15 A) EUV spectrometer (250-1450 A) to measure the solar irradiation responsible for the photoelectron production, and a hydrogen Lyman Alpha photometer to monitor the solar irradiance and geocoronal emissions.

Chakrabarti, S.↗
NASA NTRS1988

Measurements of H2O in the terrestrial mesosphere and implications for extra-terrestrial sources

Recent measurements of mesospheric water vapor and their implications for the existence of extraterrestrial sources of water are discussed. This study was prompted by the work of L. Frank and others who, based on their interpretation of transient dark spots visible in ultraviolet images of the Earth's dayglow emission, have proposed that a large flux of small comets enters the Earth's upper atmosphere each day. To date, however, analysis does not conclusively refute or support the idea of an external source.

Olivero, John J.↗