Engineering topics

Meier, R. R.

Publications and source records attributed to Meier, R. R..

At least 19 records

NASA NTRS2001

Living With a Star, the Geospace Mission Definition Team and Aeronomy

To gain an understanding of the Sun-Earth system, including how and why the sun varies, how the earth responds, and the impacts on humanity, research is needed that has a integrated and systematic approach. The Living With a Star (LWS) program represents an important element in this regard both to continued progress in space science in general and in Aeronomy in particular. A fundamental question in Aeronomy is how the variable sun affects the ionosphere, thermosphere, and mesosphere. The LWS program focuses on those areas of scientific understanding that promote progress in areas that have human impact and can be investigated with space borne instruments. The Geospace Mission Definition Team is charged with investigating the science priorities identified by the LWS Science Architecture Team and developing an approach to making the necessary measurements in concert with other missions and programs. An important aspect of this approach is that all LWS measurement programs are operating simultaneously for several years. We will review some of the areas that the LWS SAT have emphasized in Aeronomy, including understanding the effects of solar variability on ionospheric density and irregularities, the effects of solar variability on the mass density of the atmosphere at LEO altitudes, and the effects of solar variability on near-surface temperatures and on ozone distribution.

Kintner, Paul M., Jr.↗

NASA NTRS1995

Interpretation of Dynamics Explorer far UV images of the quiet time thermosphere

A selected set of far ultra violet images of Earth have been analyzed quanitatively to establish their validity for studying thermospheric weather. The set of images chosen for the study was restricted to mostly geomagnetically quiet conditions in order to obtain a baseline understanding of the relationship between the observations and thermospheric phenomenology. The images included low to modrerate solar activity levels. A new model was developed to generate global dayglow images using first principles methods. The mass Spectrometer/incoherent scatter (MSIS-86) model was used to predict the thermospheric concentrations. The analyses of thermospheric images observed in the 123 to 160-nm nominal passband show that the spectral composition for observations on the projected earth disk is dominated by O I 130.4-nm radiation (85-90%), with concentrations from O I 135.6-nm and N2 Lyman-Birge-Hopefield (LBH) bands of about 5-8% each. The synthetic images reproduce the global features of the observed images rather well. Differences between the model and the data are attributed to real atmospheric effects, such as atomic oxygen depletions which are not well reproduced by the MSIS model when geomagnetic activity is elevated. The absoute values recorded were 38-54% higher than predicted. We attribute this discrepancy to low values of the solar extreme ultraviolet irradiances used in the model. Images obtained in the 136 to 165-nm nominal passband are a factor of 2.7 greater than the model. The excess signal observed is most likely due to a long wavelength tail in the instrument sensitivity which allowed Rayleigh scattered sunlight between 180and 250nm to be detected. The understanding of the Dynamics Explorer (DE 1) images gained by this study provides the basis for future work on the global response of the theremosphere to geomagnetic forcing.

Meier, R. R.↗

NASA NTRS1993

The 200- to 300-nm radiation field in the stratosphere - Comparison of models with observation

The SABE 1 experiment (Herman and Mentall, 1982) measured the direct and scattered solar radiation at wavelengths between 190 and 320 nm from a balloon floating at 40 km altitude. We use state of the art radiative transfer models together with cross sections and solar flux data commonly used in modeling of the stratosphere to calculate the direct and scattered radiation at 40 km. The comparison between theory and experiment made by Herman and Mentall (1982) is extended. Significant discrepancies in the ratio of the scattered to direct flux not discussed in their work were found in the Schumann-Runge band and above 280 nm. Possible reasons for the differences are discussed.

Kylling, A.↗

NASA NTRS1993

A model for generating UV images at satellite altitudes

Vertical perspective, mercator, and tilted perspective projection images are presented which contain calculated dayglow, nightglow, and aurora. These images are discussed in terms of their structure's sources, which encompass composition variations, solar zenith angle changes, and changes in the path length experienced on going from disk-viewing to limb-viewing. Both a global thermospheric model (MSIS-86) and a global ionospheric model (the International Reference Ionosphere) are used to respectively specify neutral composition and the profiles of OI and OII.

Cox, R. J.↗

NASA NTRS1992

The hydrogen coma of Comet P/Halley observed in Lyman-alpha using sounding rockets

Hydrogen Lyman-alpha (121.6 nm) images of Comet P/Halley were obtained using sounding rockets launched from White Sands Missile Range on 24.5 February and 13.5 March 1986. The second rocket was launched 13 hours before the fly-by of the Giotto spacecraft. An electrographic camera on both flights provided Lyman-alpha images covering a 20 field of view with 3 arcmin resolution. The data from both flights have been compared with a time-dependent model of hydrogen kinetics. To match the measured isophote contours, hydrogen sources with velocity components of 8 km/s and 20 km/s (from OH and H2O respectively) as well as a low velocity component (about 2 km/s) are required. This low velocity component is thought to result from thermalization of fast hydrogen atoms within the collision zone, providing an important diagnostic of temperature and density near the nucleus. Hydrogen production rates of 3.8 x 10 exp 30/s and 1.7 x 10 exp 30/s have been obtained for the two observations.

Mccoy, R. P.↗

NASA NTRS1992

Atomic oxygen in the Martian thermosphere

The Mariner 9 Ultraviolet Spectrometer (UVS) made extensive observations of air-glow emissions from the thermosphere of Mars throughout the nominal mission (November 1971 - February 1972), during late summer in the southern hemisphere. Limb and disc measurements of the 130 nm triplet emission from thermospheric atomic oxygen were modelled by Strickland et al. Recently, the thermospheric general circulation models (TGCMs) developed for the Earth and Venus have been applied to Mars; we refer to it as the MTGCM. Our analysis shows that the oxygen mixing ratio is the fundamental unknown controlling the 130 nm brightness. Our radiative transport calculation shows that the emergent intensity at 130 nm is not very sensitive to variations in thermospheric temperature. The pattern of diurnal variation derived from our analysis is roughly the same as Strickland et al. although with somewhat lower values for the O mixing ratio. The main reasons for this difference are the more important role played by the photoelectron source in our model, and the somewhat larger 130 nm solar flux; thus, we require less oxygen to match the observed brightnesses. Strickland et al. also found that the OI 130 nm emission on Mars is correlated with solar activity. We find that the correlation is virtually non-existent during the early orbits when the planet was covered with a thick global dust storm, but later orbits, during the clearing of the storm, show a persistent correlation.

Stewart, A. I. F.↗

NASA NTRS1992

Atomic oxygen in the Martian thermosphere

Modern models of thermospheric composition and temperature and of excitation and radiative transfer processes are used to simulate the O I 130-nm emission from Mars measured by the Mariner 9 ultraviolet spectrometer. This paper uses the Mars thermospheric general circulation model calculations (MTGCM) of Bougher et al. (1988) and the Monte Carlo partial frequency redistribution multiple scattering code of Meier and Lee (1982). It is found that the decline in atomic oxygen through the daylight hours predicted by the MTGCM cannot be reconciled with the excess afternoon brightness seen in the data. Oxygen concentrations inferred from the data show a positive gradient through the day, in agreement with the original analysis by Strickland et al. (1973). In addition, the data suggest that the oxygen abundance increases toward high southerly latitudes, in contrast with the MTGCM prediction of high values in the Northern Hemisphere. It appears that solar forcing alone cannot account for the observed characteristics of the Martian thermosphere and that wave and tidal effects may profoundly affect the structure, winds, and composition.

Stewart, A. I. F.↗

NASA NTRS1991

Production of N(+)-asterisk from N2 + hnu - Effective EUV emission yields from laboratory and dayglow data

Photodissociative ionization of N2 into the unbound N2(+) H 2Sigma-g(+) state is identified as the parentage of a number of N(+) and N-excited states that contribute to the u.v. dayglow. Yields have been obtained for the production of extreme ultraviolet emission lines of N(+) and N from a laboratory experiment using a broadband synchrotron radiation source with fluorescence spectroscopy. The yields are termed 'effective', in that they are constant percentages of the H state cross section. These are compared wih effective yields needed to reproduce N II 1085 and 916 A lines from four dayglow observations using a model of solar energy deposition and photoelectron production and loss in the earth's thermosphere. The 1085 A effective yield measured in the laboratory (18 percent) agrees with that from the dayglow data (average of 17 percent) to well within experimental uncertainties. Thus, it is concluded that photodissociative ionization of N2 is the primary source of the N II 1085 A dayglow. However, there is an order of magnitude discrepancy among the various dayglow observations of the 1085/916 intensity ratio, only one of which is consistent with the laboratory observation of 4.4. Neither contamination by other dayglow features nor atmospheric extinction can account for the disparities. Laboratory measurements of N2 and O2 absorption cross sections at these wavelengths are also reported.

Meier, R. R.↗

NASA NTRS1991

Nitrogen airglow sources - Comparison of Triton, Titan, and earth

The individual contributions of direct solar excitation, photoelectron excitation, and magnetospheric electron excitation of Triton and Titan airglow observed by the Voyager Ultraviolet Spectrometer (UVS) are quantified. The principal spectral features of Triton's airglow are shown to be consistent with precipitation of magnetospheric electrons with power dissipation about 500 million W. Solar excitation rates of the dominant N2 and N(+) emission features are factors of 2-7 weaker than magnetospheric electron excitation. On Titan, the calculated disk center and bright limb N(+) 1085 A intensities due to solar excitation agree with observed values, while the 970 A feature is mostly N21 c5 band emission. The calculated LBH intensity by photoelectrons suggests that magnetospheric electrons play a minor role in Titan's UV airglow. On earth, solar/photoelectron excitation explains the observed N(+) 1085 A and LBH intensites and accounts for only 40 percent of the N(+) 916 A intensity.

Strobel, Darrell F.↗

NASA NTRS1990

The EUV dayglow at high spectral resolution

Rocket observations and spectra of the dayglow spectrum of the terrestrial atmosphere between 840 and 1860 A are studied. Three bands of the N2 c-prime 4 system are seen clearly resolved in the dayglow. Analysis of high-resolution N2 Lyman-Birge-Hopfield data shows no anomalous vibrational distribution as has been reported from other observations. Altitude profiles of the observed O and N2 emissions demonstrate that the MSIS-83 model O and N2 densities are appropriate for the conditions of the rocket flights.

Morrison, M. D.↗

NASA NTRS1989

An analysis of the effects of N2 absorption on the O(+) 834-A emission from rocket observations

Altitude profiles of the O(+) 834-A emission, obtained from rocket observations at moderate and high solar conditions, are compared with model calculations. The model showed that when viewing the atmosphere horizontally at altitudes below the F2 layer, the 834-A intensity was virtually independent of the O(+) density. The 834-A intensity was found to be highly sensitive to the N2 absorption cross section. Comparisons with model calculations suggest that absorption by N2 is a factor of 10 lower than the currently accepted values.

Cleary, D. D.↗

NASA NTRS1988

The OI 989 and 1173 A multiplets in the dayglow

Sounding rocket measurements of the O-I 989-A dayglow obtained in 1978, 1980, and 1985 are discussed. The 989-A intensity and multiplet ratios are consistent with total branching losses (to atomic states other than the ground state) of 1.5-4 x 10 to the -4th. It is found that the 1173/989 intensity ratio is dependent only on the 1173/989 branching ratio and the atomic oxygen concentration when viewing upward from rocket altitudes.

Morrison, M. D.↗

NASA NTRS1987

Hydrogen Balmer alpha intensity distributions and line profiles from multiple scattering theory using realistic geocoronal models

The H Balmer alpha nightglow is investigated by using Monte Carlo models of asymmetric geocoronal atomic hydrogen distributions as input to a radiative transfer model of solar Lyman-beta radiation in the thermosphere and atmosphere. It is shown that it is essential to include multiple scattering of Lyman-beta radiation in the interpretation of Balmer alpha airglow data. Observations of diurnal variation in the Balmer alpha airglow showing slightly greater intensities in the morning relative to evening are consistent with theory. No evidence is found for anything other than a single sinusoidal diurnal variation of exobase density. Dramatic changes in effective temperature derived from the observed Balmer alpha line profiles are expected on the basis of changing illumination conditions in the thermosphere and exosphere as different regions of the sky are scanned.

Anderson, D. E., Jr.↗

NASA NTRS1987

Magnetic field-aligned electric field acceleration and the characteristics of the optical aurora

The long-recognized association of brighter aurora with more deeply penetrating, and hence more energetic, electrons is examined. Using the Knight (1973) relation between the magnetic-field-aligned current density and potential drop (derived from the theory of single-particle motion in the presence of a magnetic-field-aligned electric field), an approximate expression relating the energy flux of the precipitating electrons over discrete aurora and the mean particle energy is derived. This expression is used in conjunction with an auroral optical excitation and emission model to specify the dependence of the red/blue ratio of auroral optical emissions on the brightness of the aurora. It is shown that the quantitative predictions of the discrete auroral theory are in accord with observations of the aurora.

Christensen, A. B.↗

NASA NTRS1985

The ultraviolet dayglow at solar maximum. III - Photoelectron-excited emissions of N2 and O

Rocket observations of the far ultraviolet dayglow spectrum near solar cycle maximum are analyzed using laboratory cross sections, atmospheric composition models, and photoelectron production models. Photoelectron-excited emissions of N2 and O are used to derive a self-consistent description of the atmosphere at solar maximum. Spectral synthesis of the N2 Lyman-Birge-Hopfield bands shows a departure of a 1Pi(q) state vibrational populations from the direct excitation theory. Observations of the N2 second positive (0, 0) 3371-A band and O I 1356-A emission indicate an exospheric temperature of 1600 K, 200 K higher than predicted by empirical models. The empirical models are also found to overestimate the O and O2 densities required to fit the data by a factor of 2 and 1.4, respectively. These results are compared to the results of an analysis of similar observations made in 1978 near solar minimum.

Meier, R. R.↗

NASA NTRS1984

An extreme ultraviolet spectrometer experiment for the Shuttle Get Away Special Program

An extreme ultraviolet (EUV) spectrometer experiment operated successfully during the STS-7 mission in an experiment to measure the global and diurnal variation of the EUV airglow. The spectrometer is an F 3.5 Wadsworth mount with mechanical collimator, a 75 x 75 mm grating, and a bare microchannel plate detector providing a spectral resolution of 7 X FWHM. Read-out of the signal is through discrete channels or resistive anode techniques. The experiment includes a microcomputer, 20 Mbit tape recorder, and a 28V, 40 Ahr silver-zinc battery. It is the first GAS payload to use an opening door. The spectrometer's 0.1 x 4.2 deg field of view is pointed vertically out of the shuttle bay. During the STS-7 flight data were acquired continuously for a period of 5 hours and 37 minutes, providing spectra of the 570 A to 850 A wavelength region of the airglow. Five diurnal cycles of the 584 A emission of neutral helium and the 834 A emission of ionized atomic oxygen were recorded. The experiment also recorded ion events and pressure pulses associated with thruster firings. The experiment is to fly again on Mission 41-F.

Conway, R. R.↗

NASA NTRS1982

Spectroscopy of the O I 989- and 7990-A multiplets in the dayglow and aurora

Several examples are presented to illustrate the behavior of the 989- to 7990-A complex. For the most part, these are chosen to correspond to particular observations of the airglow and aurora. In particular, the 989-A dayglow is computed for comparison with the data of Gentieu et al. (1979). In addition, line ratios are provided for comparison with the high-resolution data reported by Christensen et al. (1982). Several examples of auroral phenomena, including expected emissions from the dayside cleft region, are adduced, and the implications of high-resolution observations of line ratios and selective absorption by N2 are addressed. Finally, the utility of 989- to 7990-A multiplets as diagnostics of the atmospheric O I abundance is studied.

Meier, R. R.↗

NASA NTRS1982

An analysis of the OI 1304 A dayglow using a Monte Carlo resonant scattering model with partial frequency redistribution

The transport of resonance radiation under optically thick conditions is shown to be accurately described by a Monte Carlo model of the atomic oxygen 1304 A airglow triplet in which partial frequency redistribution, temperature gradients, pure absorption and multilevel scattering are accounted for. All features of the data can be explained by photoelectron impact excitation and the resonant scattering of sunlight, where the latter source dominates below 100 and above 500 km and is stronger at intermediate altitudes than previously thought. It is concluded that the OI 1304 A emission can be used in studies of excitation processes and atomic oxygen densities in planetary atmospheres.

Meier, R. R.↗