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NASA NTRS1987

Interferometric radar measurement of ocean surface currents

A new method of measuring surface currents using an interferometric synthetic aperture radar is presented. An airborne implementation has been tested over San Francisco Bay near the time of maximum tidal flow, resulting in a map of the east-west component of the current. Only the line-of-sight component of velocity is measured by this technique. Where the SNR ratio was strongest, statistical fluctuations of less than 4 cm/s were observed for ocean patches of 60 x 60 m.

Goldstein, R. M.↗

NASA NTRS1987

Atmosphere dynamics in the equatorial meteor zone

The study of the atmospheric circulation of the Earth from its surface to the altitudes of 100 to 110 km is essential for establishing atmospheric motion regularities with a view toward perfecting weather forecasting. The main results of the Soviet equatorial meteor expedition (SEME) are presented. A continuous cycle of measurements was carried out. Considerable interdiurnal variation of the zonal component was observed. Importantly, in the meridional component, the prevalence of a two day component was established in the equatorial meteor zone for the first time. The pronounced westward motion of the atmosphere over the equator is noted. The SEME data analysis has shown that the meteor zone is characterized by flashes of intensity of the internal gravity waves and turbulence at highest instability moments of atmosphere due to tidal motion.

Kascheev, B. L.↗

NASA NTRS1987

Lower thermosphere wind regime according to radiometeor measurements in Kazan

Research in dynamic processes in the lower thermosphere has been carried out in Kazan using the meteor radar facilities of the Kazan State University under the MAP-GLOBMET international program. Presented is experimental data on seasonal dependences of the wind for anomalous winter circulation periods, spring and autumn reconstructions and stable summer circulation from observations conducted in 1978 to 1984. Prevailing wind parameters are shown: zonal and meridional component amplitudes and A sub 0 and azimuth of the prevailing wind vector. The values are also presented for semidiurnal zonal and meridional tidal components, their correlation coefficient and zonal component amplitude maximum time.

Sidorov, V. V.↗

NASA NTRS1987

Seasonal cycling of sulfur and iron in porewaters of a Delaware salt marsh

An extensive pore water data set has been gathered in the Great Marsh, Delaware over various seasons, salinities, and tides. The data all point to a complimentary redox cycle for sulfur and iron which operates seasonally and tidally. Surface oxidizing conditions prevail in summer, with more reducing conditions at depth during the winter. During the spring tides which flood the marsh, pyrite oxidation occurs releasing excess dissolved iron (II) and sulfate to the porewaters, and precipitating authigenic solid iron phases. The redox conditions in the porewaters of the upper zone during the summer is poised between mildly oxidizing and mildly reducing conditions as shown by pE calculations. This redox environment and intermediate iron-sulfur redox species may be important for the stimulation of plant growth (photosynthesis) and sustenance of a viable microbial community (heterotrophy and chemoautropy).

Luther, George W., III↗

NASA NTRS1987

Dynamical mass transfer in cataclysmic binaries

When a binary comes into contact and mass transfer begins, orbital angular momentum is stored in the accretion disk until the disk couples tidally to the binary system. Taam and McDermott (1987) have suggested that this leads to unstable dynamical mass transfer in many cataclysmic variables in which mass transfer would otherwise be stable, and that it explains the gap between 2 and 3 h in the orbital period distribution of these systems. Here the consequences of this hypothesis for the evolution of cataclysmic binaries are explored. It is found that systems coming into contact longward of the period gap undergo one or more episodes of dynamical mass transfer.

Melia, Fulvio↗

NASA NTRS1986

Galaxies as dynamical probes of cluster structure

The effects of galaxy-cluster tidal forces on the dynamical evolution of member galaxies are investigated by means of numerical simulations. The kinds of normal events in clusters that can have significant immediate or long-term effects on galaxies are reviewed; the principal cluster properties are discussed; and the simulation results are briefly characterized, summarizing the report of Miller (1986). The degree of damage to a galaxy is found to depend strongly on the distance at which it orbits the cluster center and on the 'hardness' of the cluster potential. It is suggested that observations of the internal structure of cluster galaxies can be used to explore the cluster gravitational potential near the center and help locate and identify the nonluminous mass.

Miller, R. H.↗

NASA NTRS1988

Speculative histories of the Uranian satellite system

The hypothetical histories presently considered for the Uranian satellite system are very sensitive to the assumed satellite masses, within the errors of their determinations, as well as to the Uranian tidal effective dissipation function. A determination is made of the resonances that could have been encountered in these histories, and of the orbital eccentricity constraints that would have led to certain capture. It is found that if the mass of Miranda were of the upper extreme value, it would have been locked in a long-term 2/1 orbital resonance with Ariel to form a Laplacelike, three-body resonance that encompassed Umbriel.

Peale, S. J.↗

NASA NTRS1988

The growth of magnetic fields prior to galaxy formation

Hydromagnetic dynamo theory is applied to the problem of magnetic field amplification in the epoch after recombination but prior to galaxy formation. Large-scale density fluctuations acquire angular momentum from tidal torques exerted by neighboring fluctuations, and small-scale subfluctuations possess helicity due to the Coriolis forces associated with the rotation of the large-scale host fluctuations. Cosmic expansion and the interaction of matter with the ambient radiation field are taken into account. Despite many uncertainties, it is concluded that significant dynamo amplification may have occurred.

Zweibel, Ellen G.↗

NASA NTRS1988

A new gravitational model for the earth from satellite tracking data - GEM-T1

A computation of a terrestrial gravitational field model called the Goddard Earth Model GEM-T1 is discussed and compared to previous models, including the GEM-L2. The software tools were redesigned for the model, allowing for the optimization of the technique of relative data weighting and model estimation used in GEM solutions. The GEM-T1 model provides a simultaneous solution for a gravity model in spherical harmonics complete to degree and order 36, a subset of 66 ocean tidal coefficients for the long-wavelength components of 12 major tides, and 5-day averaged earth rotation and polar motion parameters for the 1980 period on. GEM-T1 was derived from satellite tracking data acquired on 17 different satellites whose inclinations ranged from 15 degrees to polar. A simulation of the TOPEX/POSEIDON orbit using the covariances of the GEM-T1 model was made. Estimated radial error for the simulation was reduced to less than 30 cm rms.

Marsh, J. G.↗

NASA NTRS1988

The evolution of the system of globular clusters

The physical processes affecting the evolution of the system of globular clusters are reviewed. Aspects of internal structure evolution discussed include evaporation, core collapse, expansion, tidal shocks, and interaction with other massive components of the Galaxy such as black holes, molecular clouds, and other clusters. The evolution of orbital parameters is examined, including dynamical friction, scattering by massive subcomponents, and interactions with nearby systems. In addition, an overview of the system evolution is presented.

Ostriker, Jeremiah P.↗

NASA NTRS1987

New developments in studies of compact X-ray binaries

Several recent developments, both observational and theoretical, on the study of X-ray binaries and the compact objects they contain are discussed. The recent discovery of the first binary periods for the globular cluster X-ray sources has stimulated a new model for their origin. As a variant of the 'standard' tidal capture origin model, this predicts an enhanced number of neutron stars in globular clusters. Long term timing studies of X-ray binaries may be consistent with many of these systems, primarily X-ray burst sources, being in fact hierarchical triple systems. Finally, the radio studies of Cyg X-3 and other X-ray binaries suggest that nonthermal processes are as important, energetically, as accretion processes in these systems.

Grindlay, Jonathan E.↗

NASA NTRS1988

Internal structure and shape of Mimas

The observed triaxial ellipsoid shape of Mimas, in conjunction with a mean density of 1137 kg/cu cm, is presently used as the basis of hydrostatic equilibrium and nonhydrostatic models of internal structure whose outer layers are sufficiently strong to support part of the tidal load. Such plausible internal structures are consistent with the shape and density constraints as (1) a two-layer model in hydrostatic equilibrium, (2) a hydrostatic model with four layers of equal depth, and (3) a nonhydrostatic constant-density model with an elastic lithosphere; these models admit either homogeneous or heterogeneous accretion, as well as either a cold thermal history or melting and differentiation.

Ross, M. N.↗

NASA NTRS1988

Europa - The prospects for an ocean

Tidal dissipation in the satellites of a giant planet may provide sufficient heating to maintain a liquid water ocean below a thin ice layer. In the solar system, Europa, one of the Galilean satellites of Jupiter, may have such an ocean. Both theoretical calculations and certain observations support its existence, although proof is lacking. The putative ocean would probably have temperatures, pressures, and chemistry conducive to biologic activity. However, the environment would be severely energy limited. Possible energy sources include transient transmission of sunlight through fractures in the ice and hydrothermal activity on the ocean floor. While temporary conditions could exist that are within the range of adaptation of certain terrestrial organisms, origin of life under such conditions seems unlikely. In other solar systems, however, larger satellites with more significant heat flow could provide environments that are stable over an order of aeons and in which life could perhaps evolve.

Reynolds, R. T.↗

NASA NTRS1988

The derivation of sub-canopy surface terrain models of coastal forests using synthetic aperture radar

Radar data acquired by the Shuttle Imaging Radar-B mission covering a portion of the Mouths of the Ganges forests were used to create a terrain model for use in determining tidal flow and eventual nutrient transport from the forest to the marine habitat. Results show that good digital topographic terrain models of wet coastal forests can be generated using multiple sets of L-band SAR and ancillary tide elevation data. The dominance of the interaction phenomenon in the radar backscatter of flooded forests can be used to create sub-canopy inundation maps which when merged with tide surface data can be used to generate reasonable topographic models. Ideally models could be improved by using multiple sets of data at a constant incidence angle over the total tide range. The optimal angle for the SAR depends upon the characteristics of the forest. The range of 46 to 57 deg seems applicable to the 12.5 m tall closed canopy in this example. Such models can be an extremely valuable tool for studying and mapping the mangal ecosystem.

Imhoff, M. L.↗

NASA NTRS1988

Utilizing remote sensing of thematic mapper data to improve our understanding of estuarine processes and their influence on the productivity of estuarine-dependent fisheries

The continuing disintegration of the coastal marshes of Louisiana is one of the major environmental problems of the nation. The problem of marsh loss in Louisiana is relevant to fishery management because Louisiana leads the nation in landings of fishery products, and most of the landed species are dependent upon estuaries and their associated tidal marshes. In evaluating the potential effect of marshland loss on fisheries, the first two critical factors to consider are: whether land-water interface in actual disintegrating marshes is currently increasing or decreasing, and the magnitude of the change. In the present study, LANDSAT Thematic Mapper (TM) data covering specific marshes in coastal Louisiana were used to test conclusions from the Browder et al (1984) model with regard to the stage in disintegration at which maximum interface occurs; to further explore the relationship between maximum interface and the pattern of distribution of land and water suggested by the model; and to determine the direction and degree of change in land-water interface in relation to land loss in actual marshes.

Browder, Joan A.↗

NASA NTRS1987

The origin of ultra-compact binaries

The origin of ultra-compact binaries composed of a neutron star and a low-mass (about 0.06 solar mass) white dwarf is considered. Taking account of the systemic losses of mass and angular momentum, it was found that a serious difficulty exists in the scenarios which involve tidal captures of a normal star (a main sequence star or a red giant) by a neutron star. This difficulty can be avoided if a red giant star is captured by a massive white dwarf (M is approx. greater than 1.2 solar masses), which becomes a neutron star through the accretion induced collapse.

Hachisu, Izumi↗

NASA NTRS1989

Japanese contributions to MAP

Japan contributed much to MAP in many branches. The MU (middle and upper atmosphere) radar, in operation during the MAP period, produced various novel possibilities in observations of middle atmosphere dynamics; possibilities which were fairly well realized. Gravity wave saturation and its spectrum in the mesosphere were observed successfully. Campaign observations by radars between Kyoto and Adelaide were especially significant in tidal and planetary wave observations. In Antarctica, middle atmosphere observation of the dramatic behavior of aerosols in winter is well elucidated together with the ozone hole. Theoretical and numerical studies have been progressing actively since a time much earlier than MAP. Now it is pointed out that gravity waves play an important role in producing the weak wind region in the stratosphere as well as the mesosphere.

Kato, S.↗

NASA NTRS1989

A perspective of Middle-Atmosphere Dynamics (MAD) studies at the New International Equatorial Observatory (NIEO)

The equatorial region has attracted many MAD studies mainly based on data of limited locations and resolutions. Established at NIEO are: (1) Climatology of the equatorial middle atmosphere (all of the mean zonal flow, the meridional and/or east-west circulations and the planetary/gravity waves are described based on massive, reliable data statistics); (2) Troposphere-stratosphere coupling at the equator (the candidate location of NIEO is just at the stratospheric fountain area where the tracers and waves are pumped up into the middle atmosphere); and (3) Mesosphere-thermosphere coupling at the equator; thermospheric superrotation, which may be caused either by ion drag or by tidal breaking, is examined in detail by observations covering a wide altitude range from the mesosphere through the thermosphere.

Yamanaka, M. D.↗