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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Analysis of remote measurements of tropospheric carbon monoxide concentrations made during the 1979 Summer Monsoon Experiment (MONEX)

Mixing ratios of tropospheric CO as measured by an aircraft-mounted radiometer over Saudi Arabia, the Arabian Sea, and northern India during May and June 1979 are reported. During early May, exceptionally high CO levels were detected over Saudi Arabia, and strong horizontal gradients in CO mixing ratios were seen to develop over a period of several days. Over the Arabian Sea, mixing ratios of the order of 150 parts per billion by volume were observed before the monsoon onset, and a pronounced decrease in CO was detected toward the equator. Subsequent measurements after the monsoon had become established revealed a consistent decrease in CO mixing ratio across this region. Analysis of aircraft dropsonde data and constant pressure daily streamline charts lend strong support to the hypothesis that this reduction is associated with the influx of CO-poor Southern Hemisphere air in the monsoon southwesterlies.

Doherty, G. M.↗
NASA NTRS1987

The structure and evolution of seasonal wind anomalies over the near-equatorial eastern Indian and western Pacific Oceans

The longitude-height-time structure and evolution of near-equatorial wind variability over the eastern Indian and western Pacific Oceans are studied using data obtained from a network of eight radiosonde stations extending from southern India to the central Pacific Ocean. The seasonal zonal wind anomalies observed at the cross section beween Trivandrum and Majuro stations are analyzed using an empirical orthogonal function. The Walker Circulation fluctuations are described in terms of standing oscillations in the longitude-height plane, and it is determined that Southern Oscillation propagation anomaly best represents the wind fluctuations. A complex empirical orthogonal function (CEOF) analysis and an El Nino compositing methodology are applied to the seasonal zonal wind anomalies. It is determined that the composite El Nino anomalies correspond to the spatial structure and temporal evolution of anomalies implied by the CEOF analysis.

Gutzler, David S.↗
NASA NTRS1988

Wilson cycle studies

Effort was concentrated in problems of continental evolution and a presentation was made to a workshop on the Deep Continental Growth of South India. An interpretation of the lithospheric structure of Africa as related to continental collision (together with its volcanism and topography) was prepared and a paper on this topic is about to be submitted. No expenditures were charged to the grant during this 6 month period.

Burke, Kevin↗
NASA NTRS1988

Shocked quartz and more: Impact signatures in K-T boundary clays and claystones

Quartz grains displaying multiple sets of planar features are described from numerous Cretaceous-Tertiary (K-T) boundary clays and claystones at both marine and nonmarine depositional sites around the world. All these sites also show anomalously high amounts of iridium and enrichments of other siderophile elements in cosmic ratios within these boundary units. This combination of mineralogical and geochemical features are used in support of an impact hypothesis for the end-Cretaceous event. Recently, it was suggested that some combination of explosive and nonexplosive volcanism associated with the formation of the Deccan traps in India could be responsible for the mineralogy and geochemistry seen in the K-T boundary units. Besides the obvious contradition of simultaneous explosive and nonexplosive volcanism from one locality during an instant of geologic time, there remains the difficulty of spreading both iridium (and trace elements in cosmic proportions) and quartz grains around the world by volcanic (atmospheric) transport. In addition, the ability of volcanism to produce the type of shock metamorphism seen in minerals at the K-T boundary was not demonstrated. Multiple sets of shock lamellae in quartz are considered characteristic of shock metamorphism in rocks at the sites of known impact craters and are the type of deformation seen in quartz from K-T boundary clays and claystones. Single sets of poorly defined lamellae described from rare quartz grains in certain volcanic deposits are characteristic of tectonic deformation and do not correspond to the shock lamellae in quartz from K-T sediments and impact structures. So-called shock mosaicism in quartz and feldspar grains described from volcanic deposits can result from many processes other than shock metamorphism, and therefore is not considered to be an effect characteristic solely of shock. The mineralogy of shock-metamorphosed grains at the K-T boundary also argues against a volcanic origin.

Bohor, Bruce F.↗
NASA NTRS1988

Astrophysical implications of periodicity

Two remarkable discoveries of the last decade have profound implications for astrophysics and for geophysics. These are the discovery by Alvarez et al., that certain mass extinctions are caused by the impact on the earth of a large asteroid or comet, and the discovery by Raup and Sepkoski that such extinctions are periodic, with a cycle time of 26 to 30 million years. The validity of both of these discoveries is assumed and the implications are examined. Most of the phenomena described depend not on periodicity, but just on the weaker assumption that the impacts on the earth take place primarily in showers. Proposed explanations for the periodicity include galactic oscillations, the Planet X model, and the possibility of Nemesis, a solar companion star. These hypotheses are critically examined. Results of the search for the solar companion are reported. The Deccan flood basalts of India have been proposed as the impact site for the Cretaceous impact, but this hypotheisis is in contradiction with the conclusion of Courtillot et al., that the magma flow began during a period of normal magnetic field. A possible resolution of this contradiction is proposed.

Muller, Richard A.↗
NASA NTRS1988

Nature and origin of fluids in granulite facies metamorphism

The various models for the nature and origin of fluids in granulite facies metamorphism were summarized. Field and petrologic evidence exists for both fluid-absent and fluid-present deep crustal metamorphism. The South Indian granulite province is often cited as a fluid-rich example. The fluids must have been low in H2O and thus high in CO2. Deep crustal and subcrustal sources of CO2 are as yet unproven possibilities. There is much recent discussion of the possible ways in which deep crustal melts and fluids could have interacted in granulite metamorphism. Possible explanations for the characteristically low activity of H2O associated with granulite terranes were discussed. Granulites of the Adirondacks, New York, show evidence for vapor-absent conditions, and thus appear different from those of South India, for which CO2 streaming was proposed. Several features, such as the presence of high-density CO2 fluid inclusions, that may be misleading as evidence for CO2-saturated conditions during metamorphism, were discussed.

Newton, R. C.↗
NASA NTRS1988

Kabbaldurga-type charnockitization: A local phenomenon in the granulite to amphibolite grade transition zone

In the deeply eroded Precambrian crust of South India and Sri Lanka, a series of spectacular exposures shows progressive development of coarse-grained charnockite through dehydration of amphibolite grade gneisses in different arrested stages. At Kabbaldurga, charnockitization of Archaean grey biotite-hornblende gneisses occurred about 2.5 Ga ago and evidently was induced by the influx of external carbonic fluids along a system of ductile shears and the foliation planes. The results of oxygen isotope thermometry and of geothermobarometry in adjacent areas indicate a P-T regime of 700 to 750 C and 5 to 7 kb. The decrease of water activity in the fluid infiltrated zones caused an almost complete breakdown of hornblende and biotite and the new growth of hypersthene. Detailed petrographic and geochemical studies revealed marked changes in mineralogy and chemistry from granodioritic to granitic which document the metasomatic nature of the process.

Raith, M.↗
NASA NTRS1988

The role of boron and fluids in high temperature, shallow level metamorphism of the Chugach Metamorphic Complex, Alaska

The possible role of boron (B) involvement in granite equilibria and generation of melts during crustal metamorphism has been a focus of speculation in recent literature. Most of the evidence for such involvement derives from experimental data which implies that the addition of B will lower the temperature of the granite solidus. Also the presence of tourmaline has a minor effect on the temperature of the solidus. Further indirect evidence that B may be involved in partial melting processes is the observation that granulites are commonly depleted in B, whereas the B content of low grade metapelites can be high (up to 2000 ppm). Researchers' measurements of the whole-rock B contents of granulites from the Madras region, India are low, ranging from 0.4 to 2.6 ppm. Ahmad and Wilson suggest that B was mobilized in the fluid phase during granulite facies metamorphism of the Broken Hill Complex, Australia. Thus, it appears that during the amphibolite to granulite transition, B is systematically lost from metasediments. The B that is released will probably partition into the vapor phase and/or melt phase. Preliminary measurements imply that the boron content of rocks in the Chugach Metamorphic Complex is not sufficient to influence the processes of partial melting at low pressures.

Sisson, V. B.↗
NASA NTRS1988

Granulites: Melts and fluids in the deep crust

Known examples of granulite facies metamorphism span at least 3.5 by. of Earth history. Mineralogic geobarometry indicates that such metamorphism has occurred in the deep crust, typically at 20 to 30 km (6 to 9 kbar). Geothermometry indicates that peak T = 700 to 900 C and therefore that T was elevated by at least 200 C over an anorgenic geotherm of 15 to 20 C/km. Commonly invoked sources of heat include rising magmas, radioactive decay insulated by continent/continent collision, mantle volatiles, or crustal thinning. Present day crustal thicknesses are normal beneath exposed granulite terranes and the common absence of evidence for post-metamorphic underplating suggests synmetamorphic thicknesses of 60 to 80 km. Thus granulites form in tectonically active regions of thickened crust and elevated geotherm. Xenolith suites suggest that granulite facies mineralogy persists in the deepest crust after tectonism in spite of declining temperature to greenschist/amphibolite facies conditions. The relative proportions of granulite terranes that are formed by Adirondack-type metamorphism dominantly magmatic/fluid-absent), India-type metamorphism (CO2 saturated), or some combination of 1 and 2 remains an important tectonic question.

Valley, John W.↗
NASA NTRS1988

Underplating, anatexis and assimilation of metacarbonate: A possible source for large CO2 fluxes in the deep crust

Recent models for granulite petrogenesis have involved infiltrative streaming of CO2 derived from deep-seated sources, removal of H2O in locally generated silicate melts, or various combinations of these two processes. All these models require a heat source of some type to generate the high crustal temperatures associated with anatexis and granulite-grade metamorphism, and this most likely takes the form of mantle-derived basaltic magma that is either underplated or intruded into the lower continental crust. Huppert and Sparks have recently shown that such underplating is likely to cause rapid, very large-scale melting of the overlying crust (roof rock) over time scales of only a few hundred years. This model is readily applicable to the granulite terrane of Southern India where metacarbonates occur within the deeper parts of the section including the amphibolite-granulite transition zone. Furthermore, it obviates the need to remove low melt fractions from deep crustal rocks as a principal dehydration mechanism; compaction theory has shown this to be a very sluggish process that is unlikely to be important over typical geological time scales. It also avoids any mechanism involving the subduction of large volumes of sedimentary carbonate into the mantle to provide a CO2 source.

Wickham, S. M.↗
NASA NTRS1988

Radiosonde intercomparison

The largest amount of material ever collected from a radiosonde comparison was examined. Radiosondes from Australia, Finland, India, and the United States were involved. Data were received from 100 soundings, each of which was a simultaneous in situ test of four different instrument types. The simultaneous temperature comparison of participating operational radiosondes in daylight was about 1 C at the 100 hPa level and about 4 C at the 10 hPa level, while the corresponding comparison for geopotential was about 40 meters at 100 hPa and 100 meters at 10 hPa. Estimates of the reproducibility of standard level temperatures are given. The reproducibility obtained from the in situ comparisons is, in general, slightly better than corresponding results from monitoring measurements in a real-time mode at analysis centers. Conclusions from the intercomparison are many; the following call for particular attention: (1) fully automated radiosonde systems were able to reproduce geopotential measurements better than non-automated systems, mainly due to a decrease in observer mistakes; (2) observed temperature differences between radiosonde measurements were as large during the night as during the day; and (3) significant inconsistencies still exist between the night time and day time measurements, as well as significant bias errors in the pressure measurements of some radiosonde types.

Schmidlin, F. J.↗
NASA NTRS1989

Effect of volcanic debris on stratospheric ion conductivity

The reduction is reported of stratospheric ion conductivities in the altitude range of 20 to 27 km attributable to the aerosols injected into the stratosphere by the eruption of volcano Nevado Del Ruiz on November 13, 1985. Three balloon experiments were conducted from Hyderabad, India (17.5 N, 78.6 E) carrying a Langmuir probe payload for measuring stratospheric ion conductivities. The first flight took place about 9 months before the volcanic eruption, the second 3 weeks after the eruption and the third about a year later. Lidar observations from Japan, Hawaii and Europe reported detection of aerosol layers in the 18 to 25 km altitude range attributable to the Nevado Del Ruiz volcanic eruption. A comparison of the conductivity profiles shows that the reduction of ion conductivities is: 57.3 percent at 20 km and 31 percent at 25 km. A year after the eruption, conductivities at all heights tended to recover.

Somayajulu, Y. V.↗
NASA NTRS1988

Improved ground hydrology calculations for global climate models (GCMs) - Soil water movement and evapotranspiration

A physically based ground hydrology model is presented that includes the processes of transpiration, evaporation from intercepted precipitation and dew, evaporation from bare soil, infiltration, soil water flow, and runoff. Data from the Goddard Institute for Space Studies GCM were used as inputs for off-line tests of the model in four 8 x 10 deg regions, including Brazil, Sahel, Sahara, and India. Soil and vegetation input parameters were caculated as area-weighted means over the 8 x 10 deg gridbox; the resulting hydrological quantities were compared to ground hydrology model calculations performed on the 1 x 1 deg cells which comprise the 8 x 10 deg gridbox. Results show that the compositing procedure worked well except in the Sahel, where low soil water levels and a heterogeneous land surface produce high variability in hydrological quantities; for that region, a resolution better than 8 x 10 deg is needed.

Abramopoulos, F.↗
NASA NTRS1989

Evolution of the eastern Indian Ocean since the Late Cretaceous - Constraints from Geosat altimetry

A model of the tectonic evolution of the eastern Indian Ocean from the Late Cretaceous to the present is constructed. Reinterpretations of seafloor magnetic anomalies are used to place constraints on spreading rates and the timing of major reorganizations. Vertical deflection profiles from 22 repeat cycles of Geosat altimeter data are used to determine the tectonic fabric associated with fracture zones. The Geosat data place constraints on paleospreading directions. Consideration is given to the implications of the model for the relative motions between India, Australia, and Antarctica.

Royer, Jean-Yves↗
NASA NTRS1989

Magnitude of late Quaternary left-lateral displacements along the north edge of Tibet

Images taken by the earth observation satellite SPOT of the Quaternary morphology at 18 sites on the 2000-kilometer-long Altyn Tagh fault at the north edge of Tibet demonstrate that it is outstandingly active. Long-term, left-lateral strike-slip offsets of stream channels, alluvial terrace edges, and glacial moraines along the fault cluster between 100 and 400 meters. The high elevation of the sites, mostly above 4000 meters in the periglacial zone, suggests that most offsets resulted from slip on the fault since the beginning of the Holocene. These data imply that slip rates are 2 to 3 centimeters per year along much of the fault length and support the hypothesis that the continuing penetration of India into Asia forces Tibet rapidly toward the east.

Peltzer, Gilles↗
NASA NTRS1990

Right-lateral shear and rotation as the explanation for strike-slip faulting in eastern Tibet

Bounds are placed here on the rate of rotation proposed by Cobbold and Davy (1988) for the major strike-slip faults in the eastern Tibetan Plateau. It is also concluded here that the image of lateral transport on such faults, known also as continental escape, extrusion, or expulsion, is an illusion, and that instead the left-lateral slip on east-striking plates in eastern Tibet is a manifestation of north-striking right-lateral simple shear. If this conclusion is correct, the east-striking left-lateral faults and the crustal blocks between them are rotating clockwise at 1-2 deg/Myr, the east-west dimension of eastern Tibet is shortening at 10-20 mm/yr, and little material is moving eastward out of India's path into Eursasia by left-lateral simple shear.

England, Philip↗
NASA NTRS1990

Origin of low frequency (intraseasonal) oscillations in the tropical atmosphere. III - Monsoon dynamics

The issue of the interaction of the monsoon large-scale circulation and intraseasonal oscillations is addressed, showing that, as a result of the interaction of the large scale monsoon flow with the near-equatorial intraseasonal oscillation, unstable baroclinic disturbances are generated over the monsoon region. From a linear stability analysis of quasi-geostrophic motion in a two-level model, it is shown that the westward propagating disturbances generated over the monsoon region are the manifestation of heat-induced unstable Rossby waves. The instability is favored in the region with large vertical wind shear and reduced effective static stability. The monsoon large scale circulation over India and southeast Asia and the plentiful supply of moisture in the region appear to be favorable for the development of these unstable waves.

Lau, K.-M.↗