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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Coordinated analysis of airborne spectrophotometric measurements from the mid-day auroras

Measurements made in the midday auroras are analyzed and compared to measurements from the nighttime auroras. The auroral emission features in the UV spectrum, the N2(+)ING, the N22PG, and N2VK bands, are discussed. Spectral profiles of different bands are presented, and intensity distributions are obtained. Three mechanisms are suggested which can account for the marked differences between the intensity distributions of the N2(+)ING bands of the high altitude midday auroras and the low altitude nighttime auroras: (1) differences in vibrational, rotational, and transitional temperatures; (2) resonant scattering of solar radiation; and (3) excitation of slow ions.

Sivjee, G. G.↗
NASA NTRS1974

Vibrationally excited nitrogen in stable auroral red arcs and its effect on ionospheric recombination

The time-dependent continuity equations, including diffusion, were solved for the first six energy levels of molecular nitrogen for conditions in the thermosphere corresponding to stable auroral red (SAR) arcs. The results show that molecular nitrogen is excited vibrationally to the degree that the rate constant for the ionospheric loss process, O(+) + N2 yields NO(+) + N, is increased by as much as a factor of 7.6 at F2 region altitudes. It was found that deviations from the energetically equivalent Boltzmann distribution were large, causing the rate constant to be as much as 1.6 times the rate constant calculated for the Boltzmann distribution. These results indicate that SAR arc intensities as small as 58 R can produce noticeable increases in the ionosphere ion-atom interchange reaction rate and hence in the rate of loss of ionospheric electrons. It is suggested that the observed decrease of electron density in the F2 region in SAR arcs can probably be explained by enhanced reaction rates for ion-atom interchange between O(+) and N2 caused by vibrational excitation of molecular nitrogen by electron impact.

Newton, G. P.↗
NASA NTRS1974

Vacuum UV photolysis of N2O

Emission from N2 B (3 Pi g) and O(1 S) produced during vacuum UV irradiation of N2O was studied as a function of the wavelength of the incident radiation. Two different processes were responsible for producing N2(B 3 Pi g) close to its production threshold. One process formed B 3 Pi g molecules directly and one indirectly via an unidentified precursor having a lifetime about 27 microsec. The quantum yield of O(1 S) atoms produced by photodissociation of N2O was determined as a function of incident photon energy. This yield is near 100% at 129 nm.

Mcewan, M. J.↗
NASA NTRS1975

The atmosphere of Io from Pioneer 10 radio occultation measurements

The occultation of the Pioneer 10 spacecraft by Io (JI) provided an opportunity to obtain two S-band radio occultation measurements of its atmosphere. The day-side entry measurements revealed an ionosphere having a peak density of about 60,000 el/cu cm at an altitude of about 100 km. The topside scale height indicates a plasma temperature of about 406 K if it is composed of Na(+) and 495 K if N2(+) is principal ion. A thinner and less dense ionosphere was observed on the exit (night side), having a peak density of 9,000 el/cu cm at an altitude of 50 km. The topside plasma temperature is 160 K for N2(-) and 131 K for Na(+). If the ionosphere is produced by photoionization in a manner analogous to the ionospheres of the terrestrial planets, the density of neutral particles at the surface of Io is less than 10 to 1 trillion per cu cm, corresponding to a surface pressure of less than 10 to 1 nanobars.

Kliore, A. J.↗
NASA NTRS1975

Theory and experiment of low transitions in CO discharge lasers

A self-consistent model which couples the kinetics of the electrons and heavy particles with the optical and fluid dynamic processes has been employed to identify the various parameters and explain the mechanism responsible for producing low-lying transitions in slow-flowing CO lasers. Both theory and experiment indicate that low-lying transitions can be achieved at low temperatures for low pressures (or low-flow rates) together with high partial pressures of He and N2. The role of N2 has been identified as an additive responsible for reducing the electron temperature to a range where the transfer of electrical power to the lower vibrational modes of CO is optimum.

Sidney, B.↗
NASA NTRS1975

Auroral electrons and the optical emissions of nitrogen

Simultaneous rocket measurements of the auroral electron flux and the optical emissions of N2 give a consistent picture of electron impact excitation in an aurora. The electron data show that the incident auroral electrons are nearly monoenergetic with energy about 25 keV. The overall shape of the observed low-energy electron spectrum is in good agreement with other recent observations and also with recent theoretical models, although there is some disagreement with the models in the value of the power law slope above 20 eV. A discussion of the secondary electron spectrum obtained near apogee shows that a single power law cannot accurately describe the secondary electron spectrum in the energy range from 3 to 85 eV. About 40% of the N2(+) 1NG (0,0) band emission at 3914 A is excited by electrons with energy below 85 eV.

Feldman, P. D.↗
NASA NTRS1975

Global exospheric temperatures and densities under active solar conditions

Temperatures measured by the OGO-6 satellite using the 6300 A airglow spectrum are compared with temperatures derived from total densities and N2 densities. It is shown that while the variation of the total densities with latitude and magnetic activity agree well with values used for CIRA (1972), the temperature behavior is very different. While the temperatures derived from the N2 density were in much better agreement there were several important differences which radically affect the pressure gradients. The variation of temperature with magnetic activity indicated a seasonal and local time effect and also a latitude and delay time variation different from previous density derived temperatures. A new magnetic index is proposed that is better correlated with the observed temperatures. The temperature variations at high latitudes were examined for three levels of magnetic activity for both solstices and equinox conditions. A temperature maximum in the pre-midnight sector and a minimum in the noon sector were noted and seasonal and geomagnetic time and latitude effects discussed. Neutral temperature, density, pressure and boundary oxygen variations for the great storm of March 8, 1970 are presented.

Wydra, B. J.↗
NASA NTRS1975

Supersonic CO electric-discharge lasers

Laser modeling activity is described which involved addition of an option allowing N2 as a second diatomic gas. This option is now operational and a few test cases involving N2/CO mixtures were run. Results from these initial test cases are summarized. In the laboratory, a CW double-discharge test facility was constructed and tested. Features include: water-cooled removable electrodes, O-ring construction to facilitate cleaning and design modifications, increased discharge length, and addition of a post-discharge observation section. Preliminary tests with this facility using N2 yielded higher power loadings than obtained in the first-generation facility. Another test-section modification, recently made and as yet untested, will permit injection of secondary gases into the cathode boundary layer. The objective will be to vary and enhance the UV emission spectrum from the auxiliary discharge, thereby influencing the level of photoionization in the main discharge region.

Hason, R. K.↗
NASA NTRS1976

Theory of low transitions in CO discharge lasers

A self consistent theoretical model which couples the electron and heavy particle finite rate kinetics with the optical and fluid dynamic processes has been employed to identify the various parameters and explain the mechanism responsible for producing low lying transitions in slow flowing CO lasers. It is found that lasing on low lying transitions can be achieved at low temperatures for low pressures (or low flow rates) together with high partial pressures of the He and N2. The role of N2 has been identified as an additive responsible for reducing the electron temperature to a range where the transfer of electrical power to the lower vibrational modes of CO is optimum.

Sidney, B. D.↗
NASA NTRS1976

The reactions of O(ID) and OH with CH3OH, oxidation of the HCO radial, and the photochemical oxidation of formaldehyde

An experimental, laboratory study of the various photochemical reactions that can occur in the mesosphere and stratosphere is presented. N2O was photolyzed at 2139 A in the presence of CH3OH and CO. The O(id) produced in the photolysis reacted with CH3OH to produce OH radicals, and thus the reactions of both O(id) and OH were able to be studied. Also considered was the oxidation of the HCO radical. Mixtures of Cl2, O2, H2CO, and sometimes N2 or He were irradiated at 3660 A at several temperatures to photodecompose the Cl2. The photochemical oxidation of formaldehyde was studied as follows: formaldehyde in the presence of N2 and/or O2 (usually dry air) was photolyzed with a medium pressure Hg lamp used in conjunction with various filters which transmit different relative amounts of Hg lines from 2894 A to 3660 A. Results are presented and discussed, along with a description of experimental procedures and apparatus, and chemical reaction kinetics.

Osif, T. L.↗
NASA NTRS1975

Photosynthesis of organic compounds in the atmosphere of Jupiter

An efficient conversion of CH4 to hydrocarbons and HCN takes place when NH3 is photolysed in the presence of CH4, H2, and He using a 184.9 nm light source. The extent of NH3 decomposition after a 1 hr exposure was determined spectrophotometrically; CH4, N2, and C2 and C3 hydrocarbons were detected and analyzed by mass spectrometry. Photolysis of one molar equivalent of NH3 results in the loss of 0.84 molar equivalent of CH4, which apparently reacts with hot hydrogen atoms produced by photolysis. The 8% of the NH3 which is not converted to N2 probably is converted to organic amines and nitrile derivatives. The results indicate that NH3 photolysis is a highly probable mechanism for the conversion of methane to more complex hydrocarbons in the upper atmosphere of Jupiter, and predict the occurrence of HCN, NH2NH2, and higher hydrocarbons in the Jovian atmosphere above the NH3 clouds.

Ferris, J. P.↗
NASA NTRS1976

Atomic and molecular oxygen densities in the lower thermosphere

The Atmospheric Explorer-C satellite used a neutral mass spectrometer containing a quasi-open ion source operating either in normal mode or in one that utilizes the satellite velocity to distinguish between incoming ambient particles and ambient particles which have struck instrument surfaces and become accommodated. An analysis was made of data from the mass spectrometer for those orbits when the open ion source operated either partially or entirely in the fly-through mode. A comparison of N2 density, total O density and O2/N2 density values at 200 km was made. The average N2 and O2 density values agree well with previous rocket soundings and other studies. It is believed that the individual absolute number densities obtained in the normal mode of operation are accurate to within 20% while those deduced from fly-through data may be accurate to only 30%.

Nier, A. O.↗
NASA NTRS1976

A snapshot of the polar ionosphere

This paper presents a picture of the north polar F layer and topside ionosphere obtained primarily from three satellites (Alouette 2, ISIS 1, ISIS 2) that passed over the region within a time interval of about 50 min on a magnetically quiet day. The horizontal distribution of electron densities at the peak of the F layer is found to be similar to synoptic results from the IGY. Energetic-particle and ionospheric-plasma data are also presented, and the F-layer data are discussed in terms of these measurements as well as in terms of electric-field and neutral N2 density measurements made by other satellites on other occasions. The major feature observed is a tongue of F-region ionization extending from the dayside across the polar cap, which is accounted for by antisunward drift due to magnetospheric convection. In the F layer and topside ionosphere, the main effect of auroral precipitation appears to be heating and expansion of the topside. A region of low F-layer density appears on the morning side of the polar cap, which may be due to convection and possibly also to enhanced N2 densities.

Whitteker, J. H.↗
NASA NTRS1976

A new estimate of volatile outgassing on Mars

The presence of 28% argon on Mars, as calculated by Levine and Riegler (1974) and indirectly inferred from Soviet Mars-6 lander data, has important implications for the outgassing history of H2O, CO2, and N2 on Mars. Even if the terrestrial volatile outgassing ratio is only approximately valid for Mars, then large quantities of H2O (of the order of 100,000 g/sq cm), about 10,000 g/sq cm of CO2 (about 1000 times more CO2 than found at present in the Martian atmosphere), and some 450 g/sq cm of N2 may have outgassed over the history of Mars.

Levine, J. S.↗
NASA NTRS1976

Composition and structure of the Martian atmosphere - Preliminary results from Viking 1

Results from the aeroshell-mounted neutral mass spectrometer on Viking 1 indicate that the upper atmosphere of Mars is composed mainly of CO2 with trace quantities of N2, Ar, O, O2, and CO. The mixing ratios by volume relative to CO2 for N2, Ar, and O2 are about 0.06, 0.015, and 0.003, respectively, at an altitude near 135 kilometers. Molecular oxygen is a major component of the ionosphere according to results from the retarding potential analyzer. The atmosphere between 140 and 200 kilometers has an average temperature of about 180 plus or minus 20 deg K. Atmospheric pressure at the landing site for Viking 1 was 7.3 millibars at an air temperature of 241 deg K. The descent data are consistent with the view that CO2 should be the major constituent of the lower Martian atmosphere.

Nier, A. O.↗
NASA NTRS1976

Molecular oxygen measurements at 200 km from AE-D near winter solstice, 1975

Utilizing the fly-through mode, the open source neutral mass spectrometer on Atmosphere Explorer-D (AE-D) has measured O2 densities, as well as N2 densities and in situ neutral temperatures, at midmorning during winter solstice over the latitude range 90 degrees S to 90 degrees N. The expected seasonal variation in N2 was found at 200 km together with a more complex behavior in molecular oxygen than might be expected from a diffusive equilibrium model with constant lower boundary values. Under geomagnetically quiet conditions the equatorial 200 km value of O2 was about 1.7 x 10 to the 8th/cu cm. A local maximum in the 200 km O2 densities was found near 70 degrees N, where an average quiet time value was 2.5 x 10 to the 8th/cu cm, implying a 120 km density of 8.3 x 10 to the 10th/cu cm. The in situ temperature measurements confirm the presence of higher temperatures near 70 degrees N latitude, even during geomagnetically quiet conditions.

Kayser, D. C.↗
NASA NTRS1976

Comparison of neutral temperatures inferred from instruments on the AE-C satellite

Determinations of neutral thermospheric temperature from data taken with instruments aboard the AE-C spacecraft have been compared during the circular orbit phase in late December 1974 and January 1975 when the satellite altitude was near 260 km. These temperatures are found to be in overall agreement to within about 10% during periods of low magnetic activity. The methods are based on: analysis of the satellite spin modulation of N2 density; analysis of the ion temperature; and the calculation of the temperature needed to match measured N2 and Ar densities assuming fixed boundary conditions at 120 km.

Hedin, A. E.↗
NASA NTRS1976

Large-scale neutral composition gravity waves in the thermosphere observed by ESRO 4

Neutral composition waves with a wavelength of about 5000 km and a wave period of about 2.5 h were observed by ESRO 4 in the altitude region of 250 km. The amplitudes are of the order of 25% for Ar, 15% for N2, and roughly 10% for He and O at 25 deg geographic latitude. The Ar and N2 waves are almost in phase, whereas He is in antiphase, and O is in between. The wave amplitudes are seen to decrease toward lower latitudes, suggesting that the composition waves are launched by auroral sources. Simultaneous ground-based ionosonde measurements of the F2 layer critical frequency at middle and low latitudes show a wave period consistent with the satellite observations. From the relation between wavelength and wave period these waves are identified as gravity waves. The theoretical investigation with a multicomponent model shows that diffusion plays a major role in explaining the observed phase and amplitude relations between atmospheric constituents.

Trinks, H.↗