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NASA NTRS1984

Is there radar evidence for liquid water on Mars?

The hypothesis that an extraordinary radar smoothness of a lunar target suggests that ground moisture is rest on the assumption that on the penetration-depth scale, the dielectric constant be an isotropic quantity. In other words, the planet's surface should have no vertical structure. Results of modeling exercises (based on the early lunar two-layer models) conducted to simulate the behavior of radar reflectivity, at S-band, over Solis Lacus, without manipulating the dielectric constant of the base layer (i.e., without adding moisture) are summarized. More sophisticated, explicit, rather than iterative multi-layer models involving dust, duricrust, mollisol, and permafrost are under study. It is anticipated that a paradoxical situation will be reached when each improvement in the model introduces additional ambiguities into the data interpretation.

Roth, L. E.↗

NASA NTRS1983

Progress and problems in the theory of type III solar radio emission

The experimental and theoretical status of type III solar radio emission is considered in detail. Very recent developments which are relevant to the underlying plasma physics are emphasized. In particular, the identity of the submegahertz emissions as fundamental, or second harmonic, the degree of correlation between emissivities, electron streams, and plasma (Langmuir) waves, paradoxes concerned with the time-ordering of these phenomena, and the role of background density irregularities and ion-acoustic turbulence in the solar wind, are discussed. From the theoretical point of view, the current picture of the underlying Langmuir turbulence, including such effects as the interaction between Langmuir waves and stream electrons, induced scatter off ions, and strong turbulence effects such as modulational instability and soliton collapse, is discussed.

Goldman, M. V.↗

NASA NTRS1985

Preliminary GCM Results with a New Radiation Parameterization

A new parameterization of solar and terrestrial radiation was developed and tested. The solar radiation parameterization is based on that of Lacis and Hansen (1974), but with zenith-angle-dependent surface albedoes, and revised treatments of cloudiness. The terrestrial radiation parameterization is based on the work of Chou (1984) for water vapor, Chou and Peng (1983) for carbon dioxide, and Rogers (1968) for ozone, with a new parameterization of the effects of clouds. Results obtained were compared with the new parameterizations to those obtained with the earlier parameterization described by Schlessinger (1976). Several dramatic improvements came to light. For the most part these are related to the fact that the new terrestrial radiation paramerization includes the effects of the water vapor continuum, while the earlier parameterization does not. In the moist tropical planetary boundary layer (PBL) continuum emission leads to much stronger cooling of the PBL over the oceans. Over land, however, the cooling of the PBL is significantly reduced. The latter, somewhat paradoxical result is due to the strong diurnal cycle of the continental PBL. At night the shallow continental PBL is overlain by a moist layer created by mixing during the previous afternoon. The moist upper layer acts as a radiative blanket, reducing the time-averaged radiative cooling of the continental PBL.

Randall, D.↗

NASA NTRS1985

Mineralogy and chemistry of the Earth

The Earth is the prototype if not typical terrestrial planet. Ideas about the origin, evolution, structure and chemistry of the planets can be tested most thoroughly on the Earth. Similarly, the study of the other planets has generated new ideas which may be applicable to the Earth. For example the concepts of magma oceans, large polar wander, global stress fields, buoyant lithosphere, deep cumulate reservoirs, multiple tectonic styles and crust generation may also apply to the Earth, present or past. It is no longer valid to think of the mantle as an essentially homogeneous undifferentiated shell of olivine with pockes of basalt providing melts to midocean ridges and oceanic islands. It appears to be a well differentiated, outgassed body with both radial and lateral chemical variations. The lower mantle is close to chondritic in its major element chemistry. The transition region is garnet and clinopyroxene rich and may be a major basalt reservoir. This would explain the thin crust paradox. Chemical stratification of the Earth probably occurred during accretion.

Anderson, D. L.↗

NASA NTRS1983

Reduction of display artifacts by random sampling

The application of random-sampling techniques to remove visible artifacts (such as flicker, moire patterns, and paradoxical motion) introduced in TV-type displays by discrete sequential scanning is discussed and demonstrated. Sequential-scanning artifacts are described; the window of visibility defined in spatiotemporal frequency space by Watson and Ahumada (1982 and 1983) and Watson et al. (1983) is explained; the basic principles of random sampling are reviewed and illustrated by the case of the human retina; and it is proposed that the sampling artifacts can be replaced by random noise, which can then be shifted to frequency-space regions outside the window of visibility. Vertical sequential, single-random-sequence, and continuously renewed random-sequence plotting displays generating 128 points at update rates up to 130 Hz are applied to images of stationary and moving lines, and best results are obtained with the single random sequence for the stationary lines and with the renewed random sequence for the moving lines.

Ahumada, A. J., Jr.↗

NASA NTRS1985

Some chemical and isotopic observations in chondrules

Chemical, nitrogen and noble gas isotopic observations in individual chondrules of the Bjurbole (L4) and Dhajala (H3,4) chondrites are reported. The delta N-15 is +9.4 for the Bjurbole 'matrix,' ranges from +6.4 to -20.0 in chondrules, and appears to be related to the chemical composition. Nitrogen isotope systematics seem to require the presence of more than one component of distinct signatures. Although we cannot rule out complex processes of chondrule and matrix formation involving element and isotope fractionations, the oxygen isotope systematics also seem to require distinct reservoirs. The results in terms of the lack of equilibrations among chondrule minerals are discussed, as well as with the host meteorite matter, and also the paradox of the constant Fe/Mg ratio of olivines in Bjurbole and of the majority of ordinary chondrites.

Fredriksson, K.↗

NASA NTRS1986

A palaeomagnetic perspective of Precambrian tectonic styles

The considerable success derived from palaeomagnetic studies of Phanerozoic rocks with respect to the tectonic styles of continental drift and plate tectonics, etc., have not been repeated by the many palaeomagnetic studies of Precambrian rocks. There are 30 years of research with results covering the major continents for Precambrian times that overlap considerably yet there is no concensus. There is good evidence that the usual assumptions employed by palaeomagnetism are valid for the Precambrian. The exisence of magnetic reversals during the Precambrian, for instance, is difficult to explain except in terms of a geomagnetic field that was predominantly dipolar in nature. It is a small concession to extend this notion of the Precambrian geomagnetic field to include its alignment with the Earth's spin axis and the other virtues of an axial geocentric dipole that characterize the recent geomagnetic field. In terms of greenstone terranes it is obvious that tectonic models postulated to explain these observations are paramount in understanding Precambrian geology. What relevance the current geographical relationships of continents have with their Precambrian relationships remains a paradox, but it would seem that the ensialic model for the development of greenstone terranes is favored by the Precambrian palaeomagnetic data.

Schmidt, P. W.↗

NASA NTRS1986

Preliminary assessment of soil moisture over vegetation

Modeling of surface energy fluxes was combined with in-situ measurement of surface parameters, specifically the surface sensible heat flux and the substrate soil moisture. A vegetation component was incorporated in the atmospheric/substrate model and subsequently showed that fluxes over vegetation can be very much different than those over bare soil for a given surface-air temperature difference. The temperature signatures measured by a satellite or airborne radiometer should be interpreted in conjunction with surface measurements of modeled parameters. Paradoxically, analyses of the large-scale distribution of soil moisture availability shows that there is a very high correlation between antecedent precipitation and inferred surface moisture availability, even when no specific vegetation parameterization is used in the boundary layer model. Preparatory work was begun in streamlining the present boundary layer model, developing better algorithms for relating surface temperatures to substrate moisture, preparing for participation in the French HAPEX experiment, and analyzing aircraft microwave and radiometric surface temperature data for the 1983 French Beauce experiments.

Carlson, T. N.↗

NASA NTRS1986

Geological mapping potential of computer-enhanced images from the Shuttle Imaging Radar - Lisbon Valley Anticline, Utah

Computer-enhancement techniques applied to the SIR-A data from the Lisbon Valley area in the northern portion of the Paradox basin increased the value of the imagery in the development of geologically useful maps. The enhancement techniques include filtering to remove image speckle from the SIR-A data and combining these data with Landsat multispectral scanner data. A method well-suited for the combination of the data sets utilized a three-dimensional domain defined by intensity-hue-saturation (IHS) coordinates. Such a system allows the Landsat data to modulate image intensity, while the SIR-A data control image hue and saturation. Whereas the addition of Landsat data to the SIR-A image by means of a pixel-by-pixel ratio accentuated textural variations within the image, the addition of color to the combined images enabled isolation of areas in which gray-tone contrast was minimal. This isolation resulted in a more precise definition of stratigraphic units.

Curlis, J. D.↗

NASA NTRS1985

Collisional plateaus

Aspects of the geology of collisional plateaus formed by the thickening of continental crust are briefly reviewed. The history of studies of collisional plateaus is summarized, and igneous activity in collisional plateaus is discussed. Isostatic considerations pertaining to these plateaus are addressed, developing models of isostatic support of topography which illustrate the importance of compressional tectonics in the creation of high altitude plateaus. Possible analogous environments on Venus are considered. Finally, the paradox of extension associated with compression in the plateaus is discussed.

Morgan, P.↗

NASA NTRS1987

Infrared emission and excitation in LMC HII regions

The infrared excess (IRE) of the Large Magellanic Cloud (LMC) HII nebulae is found to correlate positively with the temperature of the ambient radiation field or with the He(+)/H(+) abundance ratio. This result is discussed in terms of a selective absorption of the photons in the range 504 to 912 A relative to the He ionizing photons. This interpretation may explain the paradox of finding highly excited nebulae with only relatively moderate equivalent width of their Balmer lines.

Ungerer, V.↗

NASA NTRS1986

Another look at North Sea pole tide dynamics

The mechanism proposed by Wunsch (1974) to explain pole tide observations in the North Sea is evaluated. Wunsch's equations governing pole tide in the North Sea are presented, and solutions for correcting the depth, stream function, and deviation of the tidal height from the equilibrium values are described. The similarity between the Stokes paradox and the tidal equations of the North Sea, and the need for inclusion of inertial terms in the tidal equations are discussed.

Dickman, S. R.↗

NASA NTRS1986

Homogeneous cosmological models and new inflation

The promise of the inflationary-universe scenario is to free the present state of the universe from extreme dependence upon initial data. Paradoxically, inflation is usually analyzed in the context of the homogeneous and isotropic Robertson-Walker cosmological models. It is shown that all but a small subset of the homogeneous models undergo inflation. Any initial anisotropy is so strongly damped that if sufficient inflation occurs to solve the flatness and horizon problems, the universe today would still be very isotropic.

Turner, Michael S.↗

NASA NTRS1987

Observations of and a new model for fetch-limited wave growth

The Surface Contour Radar (SCR) is a 36-GHz computer-controlled airborne radar which generates a false-color coded elevation map of the sea surface below the aircraft in real time. In the present paper, SCR observations are discussed which demonstrate the existence of a full developed sea state. These observations are used to judge the validity of growth rates for fetch-limited wave spectrum development and lead to new refinements in the modeling of wave generation by wind. It is noted that the observations have resolved an apparent paradox in the JONSWAP and Donelan et al. (1985) fetch-limited algorithms.

Walsh, E. J.↗

NASA NTRS1987

Application of vigilance research - Rare, medium, or well done?

In the years since Mackworth (1950) initiated research into problems of human vigilance, automated systems have become more complex and costly, with greater repercussions upon failure; this has led to a paradoxical enhancement of human monitoring's importance. Applications of vigilance research to well-designed systems that take human monitoring into account are rare, although the outlook for future systems is improving. Attention is presently given to problems encountered in considerations of signal rate, length of vigil, time decrements, and two examples of implementation from commercial aviation.

Wiener, Earl L.↗

NASA NTRS1988

Particle properties and the large-scale structure of planetary rings - Rebound characteristics and viscosity

The present treatment of the apparently paradoxical reversal of momentum transport, or 'negative viscosity', in such swarms of particles on Keplerian orbits as planetary rings, illuminates the importance of particles' physical properties. Even the slightest deviation from the idealized (uniform, highly elastic, perfectly slippery, spherical) particles will affect viscosity, yielding predictions that are inconsistent with the observed ring structure. It is presently suggested that the size of the larger bodies in the rings determines random velocities, viscosity, and a substantial portion of ring structural characteristics.

Greenberg, Richard↗

NASA NTRS1988

Driving forces: Slab subduction and mantle convection

Mantle convection is the mechanism ultimately responsible for most geological activity at Earth's surface. To zeroth order, the lithosphere is the cold outer thermal boundary layer of the convecting mantle. Subduction of cold dense lithosphere provides tha major source of negative buoyancy driving mantle convection and, hence, surface tectonics. There are, however, importnat differences between plate tectonics and the more familiar convecting systems observed in the laboratory. Most important, the temperature dependence of the effective viscosity of mantle rocks makes the thermal boundary layer mechanically strong, leading to nearly rigid plates. This strength stabilizes the cold boundary layer against small amplitude perturbations and allows it to store substantial gravitational potential energy. Paradoxically, through going faults at subduction zones make the lithosphere there locally weak, allowing rapid convergence, unlike what is observed in laboratory experiments using fluids with temperature dependent viscosities. This bimodal strength distribution of the lithosphere distinguishes plate tectonics from simple convection experiments. In addition, Earth has a buoyant, relatively weak layer (the crust) occupying the upper part of the thermal boundary layer. Phase changes lead to extra sources of heat and bouyancy. These phenomena lead to observed richness of behavior of the plate tectonic style of mantle convection.

Hager, Bradford H.↗

NASA NTRS1988

Continuing the biological exploration of Mars

Mars has been an object of interest for the better part of this century. To a biologist, Mars assumes special importance because many aspects of the theory of chemical evolution for the origin of life can be tested there. The central idea of this theory is that life on a suitable planet arises through a process in which the so-called biogenic elements combine to form increasingly more complex molecules under the influence of naturally-occurring energy sources ultimately resulting in the formation of replicating organic molecules. The biogenic elements are present on Mars today. Furthermore, the available evidence also strongly suggests that Mars may have had an early history similar to that of the Earth, including a period in which large amounts of liquid water once flowed on its surface and a denser atmosphere and higher global temperatures prevailed. This is important since many lines of evidence indicate that living organisms were already present on the Earth within the first billion years after its formation at a time when the environment on Mars may have closely resembled that of Earth. Our current knowledge of the state of chemical evolution on Mars can best be described as paradoxical. Most of what we have learned has come from experiments performed on the Viking landers. The combination of planned investigations covered a broad range of techniques to detect signs of chemical evolution. The most surprising data from all of these was the absence of any detectable quantities of organic compounds at the two landing sites. On the other hand, the Viking experiments did indicate that the Martian surface samples contained unidentified strong oxidant(s) that could account for their absence.

Klein, Harold P.↗