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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

The first negative bands of N2(+) in the dayglow from the Atlas-1 Shuttle mission

While the integrated column intensities in the 0-0 band emission at 3914 A, as measured from the Atlas-1 mission, are found to be in good agreement with model values, Spacelab 1 intensities appear to have been significantly affected by vehicle-induced effects. The ion environment, in particular, appears to have been highly perturbed. The absence of the large pressurized double-Spacelab module, and the revised Space Shuttle Orbiter processing procedures, appeared to have yielded a much improved remote sensing environment.

Torr, Marsha R.↗
NASA NTRS1994

The O(+) 834-A dayglow: Revised cross sections

This study assesses the impact of new O((sup 3)P) photoionization and N2 photoabsorption cross sections, and O(+) oscillator strengths and transition probabilities, on O II 834-A airglow calculations. The 834-A intensities computed using the new emission parameters are in good agreement with rocket measurements obtained in 1978 and 1980. The present study does not support a suggested reduction in the N2 photoabsorption cross section based on an earlier analysis of the rocket data. This study also explores the problem of determining F region electron densities from satellite limb scans of the O(+) 834-A emission. Our results indicate that electron density profiles inferred from limb scans are not necessarily unique; estimates of N(sub m)F(sub 2) and h(sub m)F(sub 2) can vary by at least a factor of 2 and 50 km, respectively.

Link, R.↗
NASA NTRS1996

Analysis of EUV Dayglow Spectra of Triton, Titan and Earth

We have constructed a coupled ion and neutral chemical model of the ionosphere and thermosphere of Titan. Along with density profiles of ions and minor neutrals, we have computed the heating rates and heating efficiencies for the neutrals and chemical heating rates and efficiencies for the ions. We find that the neutral heating efficiency in our standard model varies from about 30% near 800 km to 22% near 2000 km. The most important heating processes are neutral-neutral reactions and photodissociation. The ion chemical heating rates maximize at about 10 eV cm(sup -3) s(sup -1), and the corresponding ion heating efficiencies peak near 1000 km at about 0.6%.

Fox, Jane L.↗
NASA NTRS1999

High-Resolution Spectroscopy of Auroras on Jupiter and Saturn/Earth Dayglow

The purpose of the grant was to allow the researcher to: (1) reduce and analyze Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometers (ORFEUS) II observations of Jupiter (200s) and Saturn (1200s); (2) Reduce and analyze selected ORFEUS-II Earth Far Ultraviolet (FUV) airglow data; (3) Modify existing scripts for simulating Earth FUV airglow emissions to model a subset of the ORFEUS data.

Gladstone, G. Randall↗
NASA NTRS1997

High Resolution UV Emission Cross Section for Analysis of Satellite Observations of Aurora and Dayglow of Planetary Atmosphere

A new generation of high resolution UV imaging spacecraft (Polar, Galileo, HST) are studying the airglow and aurora of the Earth and the Jovian planets. To keep pace with these technological improvements we have developed a laboratory program to provide electron collision cross sections of the major molecular planetary gases (H (sub 2) , H, O, N (sub 2) , CO (sub 2) , SO (sub 2) , O (sub 2) , H (sub 2) O, and CO).

Polar Galileo airglow aurora Earth Jovian planets.↗
NASA NTRS1993

(abstract)Electron Impact Emission Cross Sections for Modeling UV Auroral and Dayglow Observations of the Upper Atmospheres of Planets

In the upper atmospheres of the Jovian and Terrestrial planets a dominant mechanism for energy transfer occurs through electron collisional processes with neutral species leading to UV radiation. In response to the need for accurate collision cross sections to model spectroscopic observations of planetary systems, JPL has measured in the laboratory emission cross sections and medium resolution spectra of H, H(sub 2), N(sub 2), SO(sub 2), and other important planetary gases.Voyager and International Ultraviolet Explorer (IUE) spacecraft have established that band systems of H(sub 2) and N(sub 2) are the dominant UV molecular emissions in the solar system produced by electron impact. Applications of our data to models of Voyager, IUE, Galileo, and Hubble Space Telescope observations of the planets will be described.

molecular emissions↗
NASA NTRS2017

Vertical Profiles of Mars 1.27 Micrometer O2 Dayglow from MRO CRISM Limb Spectra: Seasonal/global Behaviors, Comparisons to LMDGCM Simulations, and a Global Definition for Mars Water Vapor Profiles

Since July of 2009, The Compact Reconnaissance Imaging Spectral Mapper (CRISM) onboard the Mars Re- connaissance Orbiter (MRO) has periodically obtained pole-to-pole observations (i.e., full MRO orbits) of limb scanned visible/near IR spectra (lambda= 0.4 - 4.0 micrometers, delta lambda approx. 10 nm- Murchie et al., 2007). These CRISM limb observations support the first seasonally and spatially extensive set of Mars 1.27 micometers O2 (1 delta(sub g)) day-glow profile retrievals (approx. 1100) over greater than or equal to 8-80 km altitudes. Their comparison to Laboratoire de Meteorologie Dynamique (LMD) global climate model (GCM) simulated O2 (1 delta(sub g)) volume emission rate (VER) profiles, as a function of altitude, latitude, and season (solar longitude, L(sub s), supports several key conclusions regarding Mars atmospheric water vapor (which is derived from O2 (1 delta(sub g)) emission rates), Mars O3, and the collisional de-excitation of O2 (1 delta(sub g)) in the Mars CO2 atmosphere. Current (Navarro et al., 2014) LMDGCM simulations of Mars atmospheric water vapor fall 2-3 times below CRISM derived water vapor abundances at 20-40 km altitudes over low-to-mid latitudes in northern spring (L(sub s) = 30-60 deg), and northern mid-to-high latitudes over northern summer (L(sub s) = 60-140 deg). In contrast, LMDGCM simulated water vapor is 2-5 times greater than CRISM derived values at all latitudes and seasons above 40 km, within the aphelion cloud belt (ACB), and over high-southern to mid-southern latitudes in southern summer (L(sub s) = 190-340 deg) at 15-35 km altitudes. Overall, the solstitial summer-to-winter hemisphere gradients in water vapor are reversed between the LMDGCM modeled versus the CRISM derived water vapor abundances above 10-30 km altitudes. LMDGCM-CRISM differences in water vapor profiles correlate with LMDGCM-CRISM differences in cloud mixing profiles; and likely reflect limitations in simulating cloud microphysics and radiative forcing, both of which restrict meridional transport of water from summer- to-winter hemispheres on Mars (Clancy et al., 1996; Montmessin et al., 2004; Steele et al., 2014; Navarro et al., 2014) and depend on uncertain cloud microphysical properties (Navarro et al., 2014). The derived low-to-mid latitude changes in Mars water vapor vertical distributions should reduce current model- data disagreements in column O3 and H2O2 abundances over low-to-mid latitudes (e.g., within the ACB; Lefevre et al., 2008; Encrenaz et al., 2015; Clancy et al., 2016). Lastly, the global/seasonal average com- parison of CRISM and LMDGCM O2 (1 delta(sub g)) VER below 20 km altitudes indicates a factor of approx. 3 times lower value (0.25 x 10(exp -20) cu cm sec(exp -1)) for the CO2 collisional de-excitation rate coefficient of O2 (1 delta(sub g)) than derived recently by Guslyakova et al. (2016).

Clancy, R. Todd↗
NASA NTRS1992

H I Lyman alpha emission from Saturn (1980-1990)

The characteristics of the H I Ly alpha dayglow and auroral emissions from Saturn are investigated by analyzing observations made aboard the IUE satellite on Saturn over the 1980-1990 decade (covering a complete solar activity cycle). It was found that, in this period, the dayglow emission from Saturn had significant long-term variability, with decreasing disk brightness between 1980 and 1984 and increasing brightness, as well as increased short-term (days to months) variability, between 1987 and 1990. Both the long-term and short-term variability in the Saturn Ly alpha dayglow were strongly correlated with several different solar indices. Neither the dayglow nor the auroral emission exhibited any dependence on magnetic longitude. Attempts to observe auroral activity associated with a major solar flare which produced unprecedented geomagnetic activity in March 1989 were not successful.

Mcgrath, Melissa A.↗
NASA NTRS1973

Polarization of the 584- and 304-Angstrom emissions of helium in the geocorona and interplanetary medium

The polarization of the 584- and 304-A emissions of helium that have been resonantly scattered in the earth's atmosphere and in the interplanetary medium is discussed. It is shown that in the geocorona the simultaneous measurement of altitude profiles of the 584-A He dayglow intensity and polarization will test the hypothesis that the 584-A dayglow is excited by resonance scattering of sunlight from geocoronal helium. If this is indeed the major source of the 584-A dayglow emission, a simultaneous measurement of the polarization and the altitude profile of the intensity in the exosphere will uniquely determine the helium number density distribution as a function of altitude, and in the thermosphere it will alow a study of nondiffusive equilibrium processes. An attractive feature of this method is that the interpretation does not require a knowledge of the solar 584-A line center flux or line profile.

Kumar, S.↗
NASA NTRS1982

Eddy diffusion at Saturn's homopause

Measurements of Saturn's He 584 A dayglow and the CH4 density profile deduced from stellar occultation data near the homopause have been combined to infer an eddy diffusion coefficient of 8 + or - 4 x 10 to the 7th sq cm/s and a temperature of 125 + 40 or - 25 K near the homopause at Voyager 2 encounter. It appears that the eddy diffusion coefficient may have increased between the Voyager encounters. Saturn's H Ly-alpha dayglow is qualitatively compatible with this increase and the interpretation of the He 584 A dayglow and CH4 absorption measurement.

Sandel, B. R.↗
NASA NTRS1989

Search for atmospheric holes with the Viking cameras

Images taken with the two ultraviolet cameras on board the Viking spacecraft were examined for evidence of transient decreases in the near-nadir dayglow. Comparison of near-limb observations of dayglow intensities with those at smaller angles to the nadir with the camera sensitive to O I 130.4 nm emissions supports the existence of transient decreases in the near-nadir dayglow. However, the amount of near-nadir imaging is severely limited and only several significant events are found.

Frank, L. A.↗
NASA NTRS1991

Collisional excitation and radiative properties of N II - The strong intercombination (1D - 3P0) transition at 748 A

Laboratory measurements of EUV emission from electron-excited N2 have been obtained at medium resolution, providing N II EUV emission cross section measurements and allowing the confirmation of recent calculations by Fawcett (1987) indicating the presence of a strong intercombination line in N II at 748.37 A. The most recently available data are used to predict the basic collisional and radiative properties of N II, the plasma diagnostic properties are briefly explored, and radiative cooling coefficients are given. Some basic properties of electron-excited N II and N2 are examined in the EUV in order to diagnose emission spectra of the earth and Titan. The N II emissions in the earth dayglow, particularly at 916 A, are much brighter than current estimates of source rates. The N II 1085 A line in the dayglow contains a significant component from dissociative photoionization excitation. The N II 1085 A, 916 A, and 670 A lines in the Titan dayglow spectrum appear to be compatible with direct electron excitation of N2.

Tripp, T. M.↗
NASA NTRS1993

Atmospheric holes and small comets

Global images of Earth's UV dayglow as gained with an imaging photometer on board Dynamics Explorer 1 exhibit transient decreases, or atmospheric holes, in the dayglow intensities over areas with diameters about 50 km. Features of these atmospheric holes include (1) preferential motion in the east-to-west direction across the sunlit face of Earth, (2) similar diurnal variations in occurrence rates as those for radar meteors, (3) correlation of the occurrence rates with the nonshower rates as determined with forward scatter radar, and (4) larger angular diameters for these atmospheric holes when the spacecraft approaches Earth during its perigee passes. These atmospheric holes are interpreted in terms of obscuration of the dayglow by water clouds from the disruption and subsequent vaporization of small comets at low altitudes above the atmosphere. Supporting evidence for the existence of these small comets is given by their telescopic sighting at greater altitudes before disruption and the detection of water bursts in Earth's upper atmosphere. The small-comet hypothesis and its relationship to geophysical, lunar, and interplanetary phenomena are discussed.

Frank, L. A.↗
NASA NTRS1994

Use of FUV auroral emissions as diagnostic indicators

In an earlier study we modeled selected Far Ultraviolet (FUV) auroral emissions (O I(1356 A), N2 Lyman-Birge-Hopfield (LBH) (1464 A), and LBH (1838 A)) to examine the sensitivity of these emissions and their ratios to likely changes in the neutral atmosphere. In this paper we extend that study to examine the dependence of these same emissions and their ratios on the shape of the energy distribution of the auroral electrons. In particular, we wish to determine whether changes in energy spectra might interfere with our determination of the characteristic energy. Modeled column-integrated emissions show relatively small (less than 30%) dependences on the shape and width of the incident energy spectrum, provided the average energy and total energy flux of the energy distribution are held constant. Long-wavelength FUV emissions, which are relatively unaffected by O2 absorption losses, exhibit virtually no dependence on the shape of the incident energy distribution. Changes in ratios of FUV short- to long-wavelength emissions as a function of characteristic energy are much larger than those due to changes in energy distribution. As a result, the determination of characteristic energy using these emission ratios is relatively unambiguous. We also examine the relative intensities of the aurora and the dayglow for various conditions. The intensities of modeled FUV auroral emissions relative to the dayglow emissions are presented as a function of solar zenith angle and incident energy flux. Under certain conditions (energy flux less than or equal 1 erg/sq cm/s and solar zenith angle less than or equal 50 deg) the dayglow will be limiting factor in the detection of weak auroras.

Germany, G. A.↗
NASA NTRS1998

Molecular Processes in Comets

The research focused on molecular hydrogen and its response to ultraviolet radiation, photoelectron impact excitation and X-ray radiation and on the interpretation of the ultraviolet spectra of the Jupiter dayglow and auroras. A systematic effort was made to obtain reliable rate coefficients for rovibrational energy transfer of H2, particularly in collisions with hydrogen atoms. We carried out elaborate quantum-mechanical calculations of the scattering of H and H2 on what had been characterized as a reliable potential energy surface of the H3 molecular system. These calculations took into account reactive channels and rate coefficients for ortho-para transitions were obtained. Quantal calculations are too complex to be applied to all the possible rovibrational transitions and we turned to a semi-classical method. With it we calculated rate coefficients for transitions, reactive and non-reactive, for all the rovibrational levels. We carried out the calculations for three of the available H3 potential energy surfaces. We discovered an unexpected sensitivity of the rate coefficients for the non-reactive channels to the potential energy surface. This discovery stimulated more thorough investigations of the potential energy surface elsewhere and to the construction of a new surface. We have used it in further semi-classical calculations in work that will shortly be 2 completed and which, together with new quantum-mechanical calculations should comprise a set of reliable rate coefficients that can be used in discussions of H2 on the Jovian planets. We carried out a detailed study of the Jovian ultraviolet dayglow. There has been a long-running argument about the dayglow on Jupiter. There are two sources of excitation: fluorescence and photoelectron impact excitation. It had been argued that a third source "the electron glow" was needed to bring theory and observation into agreement. We believe we have shown conclusively that the third source is unnecessary. We have achieved a close quantitative agreement between the predicted spectrum arising from fluorescence and photoelectrons and the measured spectrum. We also demonstrated a method by which the presence of HD could be established observationary. Similar calculations were carried out of the ultraviolet spectra of the Jovian auroras. We again found close agreement. Indeed, the agreement was so detailed we were able to derive the temperature of the atmosphere. We found, contrary to the standard model of the time, a high temperature between 400 K and 600 K and established the presence of a significant temperature gradient. A large temperature gradient was indeed found by direct sampling with the Jupiter probe.

Dalgarno, A.↗
NASA NTRS1978

Helium glow detector experiment, MA-088

Of the two 584 A channels in the helium glow detector, channel #1 appeared to provide data with erratic count rates and undue susceptibility to dayglow and solar contamination possibly because of filter fatigue or failure. Channel #3 data appear normal and of high quality. For this reason only data from this last channel was analyzed and used for detailed comparison with theory. Reduction and fitting techniques are described, as well as applications of the data in the study of nighttime and daytime Hel 584 A emission. A hot model of the interstellar medium is presented. Topics covered in the appendix include: observations of interstellar helium with a gas absorption cell: implications for the structure of the local interstellar medium; EUV dayglow observations with a helium gas absorption cell; and EUV scattering from local interstellar helium at nonzero temperatures: implications for the derivations of interstellar medium parameters.

Bowyer, C. S.↗