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NASA NTRS1983

Mapping electrostatic potentials from the ionosphere to the magnetosphere

Techniques for mapping observed ionospheric-potential distributions into the magnetosphere are discussed and illustrated using published Millstone Hill and Chatanika incoherent-scatter-radar data. It is shown that the mapping of a given field line to the equator is subject to strong diurnal and seasonal variations (attributed to the combination of internal and tail-current magnetic-field sources at auroral latitudes and the diurnal variation of solar declination in dipole coordinates) and longitude-dependent differences in ionospheric geometry. A mapping based on the tilt-dependent model of Olson and Pfitzer (1977) and using an empirical ionospheric-potential distribution derived from Chatanika plasma-drift measurements produces a relativity uniform magnetospheric electric field in the tail region. The field at 12 earth radii (Re) is found to be between 1 and 2 kV/Re; at the dawn-dusk meridian beyond the plasmasphere it is as high as 5 kV/Re. The plasmasphere is shown to have a dusk bulge in its equipotential structure and to be almost symmetric about the dawn-dusk meridian.

Sojka, J. J.↗

NASA NTRS1984

Studies of the Virgo Cluster. I - Photometry of 109 galaxies near the cluster center to serve as standards

Attention is given to the technical aspects of photometric measurements of 109 galaxies near the center of the Virgo Cluster, noting various types of radii and surface brightness for about 50 E and dE galaxies in the sample that range in absolute magnitude from -20 to -12. These data are combined with data from the literature for giant E and dwarf E galaxies in the Local Group to study the systematic properties of E galaxies over a range of one million luminosities. The radial intensity profiles derived are fitted to the manifold of King (1978) models to derive model-dependent central surface brightness, core radii, and cutoff radii.

Sandage, A.↗

NASA NTRS1984

Equatorial ozone profiles from the Solar Maximum Mission - A comparison with theory

The UV spectrometer polarimeter on the Solar Maximum Mission has been utilized to measure mesospheric O3 altitude profiles by the technique of solar occultation. Sunset data are presented for 1980, during the fall equinoctal period within + or - 20 deg of the geographic equator. Mean O3 concentrations are (40, 16, 5.5, and 1.5) x 10 to the 9th/cu cm at 50, 55, 60, and 65 km, respectively. Some profiles exhibit altitude structure which is wavelike. The mean O3 profile is fit best with the results of a time-dependent model if the assumed water-vapor mixing ratio employed varies from 6 ppm at 65 km.

Aikin, A. C.↗

NASA NTRS1984

The HEAO 1 A-4 catalog of high-energy X-ray sources

Results are reported from an all-sky survey carried out at high X-ray energies (13-180 keV) from August 1977 until January 1979 using data obtained with the UCSD/MIT Hard X-Ray and Low-Energy Gamma-Ray Instrument on the HEAO 1 satellite. Visual displays are presented which indicate qualitatively the location, intensities, and time variability of the detected high-energy X-ray sources. A model-dependent procedure for the quantitative analysis of the sky survey data is described. The results of this procedure are presented in tabular form and include fitted count rates in four broad energy bands for about 70 sources. All sources which were detected at a level of statistical significance of not less than about 6 sigma were clearly evident in the visual displays of sky survey data. The survey is therefore complete, except in regions of source confusion, down to an intensity level of about 1/75 of the Crab Nebula in the 13-80 keV band. Forty-four sources were detected in the 40-80 keV energy band, and 14 were detected in the 80-180 keV band. Although most of the detected sources are galactic, seven are extragalactic.

Levine, A. M.↗

NASA NTRS1984

Models of the hard X-ray spectrum of AM Herculis and implications for the accretion rate

Phenomenological fits to the hard X-ray spectrum of AM Hercules have failed to explain the high equivalent width (0.8 + or - 0.1 keV) of Fe K-alpha emission. The scattering and fluorescent line production in a cold or partially ionized accretion column of hard X-rays emitted at the base are investigated using the Monte Carlo method. It is shown that the Fe emission equivalent width observed in the spectrum of AM Her can be explained without resorting to an overabundance of Fe in the accreting material. For sufficient optical depth across the accretion column, equivalent widths of K-alpha emission even larger than the observed values can be obtained. The accretion rate and gravitational power can be deduced from the optical depth across the column, if the column size is known, and, together with the observed hard X-ray and polarized light luminosities, imply a lower limit for the luminosity in the UV to soft X-ray range, for which the observations give model-dependent values.

Swank, J. H.↗

NASA NTRS1984

The Moon's orbit history and inferences on its origin

A frequency dependent model of tidal friction was used to determine the evolution of the Earth-Moon system. The analysis considers the lunar orbit eccentricity and inclination, the solar tide on the Earth, Earth oblateness, and higher order terms in the tidal potential. A solution of the equations governing the precession of the Earth's rotational angular momentum and the lunar ascending node is found. The history is consistent with a capture origin for the Moon. It rules out the origin of the Moon by fission. Results are shown for a range of assumed values for the lunar tidal dissipation. Tidal dissipation within the Moon, during what would be the immediate postcapture period, is shown to be capable of significantly heating the Moon. The immediate postcapture orbit has a periapsis within the Earth's Roche limit. Capture into resonance with the Earth's gravitational field as this orbit tidally evolves is suggested to be a mechanism to prevent so close, an approach. It is shown that the probability of such capture is negligibly small and alternative hypotheses for the survival of the Roche limit passage is offered.

Conway, B. A.↗

NASA NTRS1984

Identification of dynamic coefficients of annular turbulent seals

An identification procedure to determine dynamic coefficients of annular turbulent seals in turbopumps is presented. Measurements were carried out at a built test rig with two symmetrical arranged seals. A rigid rotating shaft is surrounded by an elastically supported housing, which is excited by impact forces. The relative radial motion between the rotating parts and the housing, respectively between the seal surfaces, is measured by displacement pick-ups and from the time signals complex frequency response functions can be calculated. Finally an analytical model, depending on the seal parameters, is fitted to the measured data, to find the dynamic coefficients.

Nordmann, R.↗

NASA NTRS1984

Comparison of Optimum Interpolation and Cressman Analyses

The objective of this investigation is to develop a state-of-the-art optimum interpolation (O/I) objective analysis procedure for use in numerical weather prediction studies. A three-dimensional multivariate O/I analysis scheme has been developed. Some characteristics of the GLAS O/I compared with those of the NMC and ECMWF systems are summarized. Some recent enhancements of the GLAS scheme include a univariate analysis of water vapor mixing ratio, a geographically dependent model prediction error correlation function and a multivariate oceanic surface analysis.

Baker, W. E.↗

NASA NTRS1985

Spacecraft-environment interaction: The environmental plasma aspect

The effects involved in the interaction between an obstacle and a space plasma can be divided into: (1) effects on the obstacle itselt (i.e., its charging); and (2) effects on the environmental plasma due to the motion of the obstacle (i.e., the creation of shocks ahead of the obstacle and complicated wakes behind the obstacle). In the wake (or antisolar direction), plasma oscillations are excited and instabilities, wave-particle interactions, turbulence, etc., are believed to take place. The effects on the obstacle and on the environmental space plasma are coupled. Hence, simultaneous solutions to the Vlasov (or Boltzmann) and Poisson equations are sought. To obtain realistic solutions of practical use, three-dimensional and time-dependent models of the interaction are needed. Achieving the latter is indeed not simple.

Samir, U.↗

NASA NTRS1985

Surface Units on Venus Derived from Pioneer-venus Altimetry, Roughness, and Reflectivity Measurements

The nature of the Venusian surface was revealed by Pioneer-Venus (PV) observations to be diverse at scales from tens to hundreds of kilometers. Spatial correlations of elevation, surface roughness, and radar reflectivity were investigated as a means of assessing the degree of homogeneity of surface radar properties within topographic provinces and develop a map of possible geologic boundaries. Correlations were performed in a supervised fashion whereby unit boundaries were selected on the basis of statistical and empirical studies of the individual data sets. Interpretations of these units in terms of geologic characteristics are based on the determination of physical units which are model dependent.

Peterfreund, A. R.↗

NASA NTRS1985

Shape of Io

An approach for measuring the triaxial shape of Io from Voyager images is described. Triaxial shape of a satellite is detrmined by comparing the theoretical shape and location of the body's limb and terminator curves with the actual curves observed in the two dimensional images. Limb or terminator points are found by matching a model for the limb profile with the actual appearance of the limb in the digital data. The theoretical model for the limb model depends on the viewing and illumination geometry, the satellite reflection characteristics and the camera 'point spread function'. The method is applied to imaging data taken of Io in the last 25 hours befor Voyager 1's closet approach to the satellite.

Synnott, S. P.↗

NASA NTRS1985

Comparison of Optimum Interpolation and Cressman Analyses

The development of a state of the art optimum interpolation (O/I) objective analysis procedure for use in numerical weather prediction studies was investigated. A three dimensional multivariate O/I analysis scheme was developed. Some characteristics of the GLAS O/I compared with those of the NMC and ECMWF systems are summarized. Some recent enhancements of the GLAS scheme include a univariate analysis of water vapor mixing ratio, a geographically dependent model prediction error correlation function and a multivariate oceanic surface analysis.

Baker, W. E.↗

NASA NTRS1985

The westward thermospheric jet-stream of the evening auroral oval

Ground-based and satellite measurements of the thermospheric wind in jet-streams during the evening auroral oval are analyzed, in order to study the geophysical mechanisms of thermospheric wind generation. Numerical simulations using a global, three-dimensional, time-dependent model of thermospheric dynamics were compared with the satellite data, and the results are discussed in detail. The wind distribution during the storm is shown in a series of color plates.

Rees, D.↗

NASA NTRS1985

Review of research on wave mean flow interactions using FGGE data

Comparison is made between the conventional Eulerian diagnostics of wave mean flow interactions in the atmosphere and the diagnostics introduced by Andrews and McIntyre (1976). In the latter, the meridional circulation is represented by a residual circulation, and the eddy torque in the zonal momentum equation by the Eliassen-Palm (1960) flux divergence (or equivalently, by the poleward eddy flux of geostrophic potential vorticity). It is found that, while the new diagnostics are useful in studying stratospheric warmings and transports of conservative quantities, the conventional diagnostics are more useful in studying global energetics and wave mean flow interactions in the troposphere and lower stratosphere. Case studies diagnosed with FGGE IIIb data are presented to illustrate this point. Kung and Tanaka's (1983) comparisons of the atmospheric energy cycle for SOP-1 and SOP-2, estimated with the use of the ECMWF and GFDL FGGE IIIb data bases, are used to assess the uncertainty in calculations of energetics based on the use of FGGE IIIb data. These results demonstrate the high degree of model dependence in the FGGE IIb data sets.

Pfeffer, R. L.↗

NASA NTRS1985

Some new results concerning the dynamic behavior of annular turbulent seals

The dynamic characteristics of annular turbulent seals applied in high pressure turbopumps can be described by stiffness, damping, and inertia coefficients. An improved procedure is presented for determining these parameters by using measurements made with newly developed test equipment. The dynamic system seal, consisting of the fluid between the cylindrical surfaces of the rotating shaft and the housing, is excited by test forces (input), and the relative motion between the surfaces (output) is measured. Transformation of the input and output time signals into the frequency domain leads to frequency response functions. An analytical model, depending on the seal parameters, is fitted to the measured data in order to identify the dynamic coefficients. Some new results are reported that show the dependencies of these coefficients with respect to the axial and radial Reynolds numbers and the geometrical data of the seal.

Massmann, H.↗

NASA NTRS1986

The cosmic ray spectrum above 10(17) eV

The final analysis of the data obtained by the Sydney University Giant Airshower Recorder (SUGAR) is presented. The data has been reanalysed to take into account the effects of afterpulsing in the photomultiplier tubes. Event data was used to produce a spectrum of equivalent vertical muon number and from this a model dependent primary energy spectrum was obtained. These spectra show good evidence for the Ankle: a flattening at 10(19) eV. There is no sign of the cut-off which would be expected from the effects of the universal black body radiation.

Winn, M. M.↗

NASA NTRS1985

Time dependent chemistry in dense molecular clouds. I - Grain surface reactions, gas/grain interactions and infrared spectroscopy

For the fist time, a time-dependent model is described which includes the role of grains in the production of molecules in dense clouds including ion-molecule gas phase chemistry. The approach provides information regarding the coupling between the two phases. Although the coupling between the two chemistries is extremely strong, the two domains maintain their own identities. While H2O, CH4, and NH3 are made efficiently, with a high production rate on grains and released back to the gas phase, the gas phase is essentially responsible for the formation of CO, a very stable molecule which may or may not react on grains with atomic oxygen and may or may not form CO2.

Dhendecourt, L. B.↗

NASA NTRS1986

Time-dependent coronal shock acceleration of energetic solar flare particles

A global time-dependent model is presented for the coronal and interplanetary shock acceleration and propagation of energetic solar flare particles. The calculations are carried out to help prove that coronal shock acceleration of solar flare particles is responsible for energetic solar flare event data gathered in interplanetary space. The model is based on the theory of diffusive shock acceleration, and requires particle speeds to be much greater than bulk velocities. Also, sufficient scattering must occur upstream and downstream of the shock for the particle scattering mean free path to be smaller than the characteristic scale lengths, which causes the same particles to encounter the shock repeatedly. A spherically symmetric shock wave is assumed, which leads to the same emission configuration for impulsively and monoenergetically emitted particles. Consideration is given to acceleration by compression at the shock front, adiabatic deceleration in the divergent downstream flow, the temporal evolution of the shock and the three-dimensional geometry of the corona. The model is used to generate normalized proton omnidirectional distributions at 1 AU and at the shock front. The spectral exhibit trends similar to those in observational data, especially proton acceleration times and the proton distribution profiles at 1 AU.

Lee, M. A.↗