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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

On the dynamics of intraseasonal oscillations and ENSO

This paper investigates some basic properties of low-frequency phenomena in the tropical atmosphere and the coupled ocean-atmosphere system, with an aim of seeking a unified dynamical framework for studies of the mechanisms of intraseasonal oscillations and the El Nino Southern Oscillation (ENSO). The role of specific processes leading to intraseasonal oscillations and to ENSO, both separately and collectively, are considered, using a simple shallow-water system. The results demonstrated the effect of including a time-dependent moist atmosphere in studies of the coupled atmosphere-ocean system. It is suggested that the interaction of several atmospheric processes and oceanic processes through evaporation-SST feedback and wind stress at the atmosphere-ocean interface may be important for the onset and evolution of an ENSO event.

Lau, K.-M.↗
NASA NTRS1988

Magnetic microspherules associated with the K/T and upper Eocene extinction events

Magnetic microspherules were identified in over 20 K/T boundary sites, and in numerous Deep Sea Drilling Project (DSDP) cores from the Caribbean and Pacific, synchronous with the extinction of several radiolarian species near the end of the Eocene. The K/T magnetic spherules are of particular interest as carriers of Ir and other siderophiles generally found in abundance in K/T boundary clay. Furthermore the textures and unusual chemistry of their component magnetic phases indicate an origin at high temperature, possibly related to (an) unusual event(s) marking the end of the Cretaceous and Eocene periods. Their origin, along with the non-magnetic (sanidine) spheules, is generally ascribed directly to megaimpact events hypothesized to have periodically disrupted life on Earth. A survey of microspherical forms associated with known meteorite and impact derived materials reveals fundamental differences from the extinction related spherules. Low temperature magnetic experiments on the K/T and Upper Eocene spheroids indicate that, unlike tektites, extremely small superparamagnetic carriers are not present in abundance. The extensive subaerial exposure of Cretaceous combustible black shale during sea level regression in the latest Cretaceous represents a potential source for the magnetic spheroids found in certain K/T boundary clays. The recent discovery of high Ir abundances distributed above and below the K/T boundary within shallow water sediments in Israel, which also contain the most extensive known zones of combustion metamorphism, the so called Mottled Zone, adds a further dramatic footnote to the proposed association between the magnetic spheroids and combustion of organic shales. Interestingly, the Mottled Zone also contains the rare mineral magnesioferrite, which was identified both within the K/T magnetic spheroids and as discrete crystals in boundary clay from marine and continental sites.

Cisowski, Stanley M.↗
NASA NTRS1988

Selective extinction of marine plankton at the end of the Mesozoic era: The fossil and stable isotope record

Floral, faunal and stable isotope evidence in a continuous sequence of latest Cretaceous and earliest Tertiary shallow water marine deposits in the Mangyshlak Peninsula, USSR suggest severe environmental changes at the Cretaceous/Tertiary (K/T) boundary. Time frame is provided by nanno, micro and macrofossils as well as by magnetic stratigraphy and an iridium spike. Oxygen isotopic analyses of the bulk sediments, composed of nanno and microplankton skeletal remains, show a sharp positive spike at the K/T boundary. This shift is primarily attributed to severe cooling possibly accompanied by increased salinities of the surface mixed layer. Floral and faunal extinctions were selective, affecting approximately 90 percent of the warm water calcareous phyto and zooplankton genera in the Tethyan-Paratethyan regions. These highly diverse taxa with many endemic representatives were at the peak of their evolutionary development. Geologic evidence indicates that the terminal Cretaceous temperature decline was coeval with widespread and intense volcanic activity which reached a peak at the close of the Mesozoic Era. Increased acidity temporarily prohibited calcite nucleation of the surface dwelling warm-water plankton. Superimposed upon decreased alkalinity, severe and rapid climatic changes caused the extinction of calcareous phyto and zooplankton.

Herman, Y.↗
NASA NTRS1988

Cretaceous-Tertiary findings, paradigms and problems

The asteroid hypothesis has stimulated numerous studies of the paleontological record at Cretaceous/Tertiary time as well as of geological indicators of environmental crisis preserved in the rock record. Both extinctions and geological anomalies often occur at times that do not appear to be synchronous or instantaneous. The record includes paleontological indicators of dinosaurs, terrestrial flora, marine planktonic organisms, and shallow water marine macrofauna and geological phenomena include occurrences of iridium and other platinum metals, trace elements, clay mineralogy, shocked minerals, soot, microspherules, and isotopes of osmium, strontium and carbon. These findings are reviewed in the context of the alternate hypotheses of an exogenic cause, involving either a single asteroid impact or multiple commentary impacts, and an endogenic cause, involving intense global volcanism and major sea level regression.

Officer, C. B.↗
NASA NTRS1989

Dynamical characteristics of tropical plumes

The effect of the barotropic interaction of tropical waves on the initial development of tropical plumes is investigated. A tropical plume from January 1979 is studied using FGGE data. The zonal wind, planetary-scale features, and relative vorticity are analyzed. An one-layer, shallow water, grid point model is utilized to examine the stability of inviscid, horizontally-sheared, barotropic basic states with respect to synoptic-scale perturbation. The data reveal a localized strengthening of cross-equatorial flow in some regions.

Askue, C. A.↗
NASA NTRS1989

Finite element analysis in fluids; Proceedings of the Seventh International Conference on Finite Element Methods in Flow Problems, University of Alabama, Huntsville, Apr. 3-7, 1989

Recent advances in computational fluid dynamics are examined in reviews and reports, with an emphasis on finite-element methods. Sections are devoted to adaptive meshes, atmospheric dynamics, combustion, compressible flows, control-volume finite elements, crystal growth, domain decomposition, EM-field problems, FDM/FEM, and fluid-structure interactions. Consideration is given to free-boundary problems with heat transfer, free surface flow, geophysical flow problems, heat and mass transfer, high-speed flow, incompressible flow, inverse design methods, MHD problems, the mathematics of finite elements, and mesh generation. Also discussed are mixed finite elements, multigrid methods, non-Newtonian fluids, numerical dissipation, parallel vector processing, reservoir simulation, seepage, shallow-water problems, spectral methods, supercomputer architectures, three-dimensional problems, and turbulent flows.

Chung, T. J.↗
NASA NTRS1990

Stability of stationary barotropic modons by Lyapunov's direct method

A new Liapunov stability condition is formulated for the shallow-water equations, using a gage-variable formalism. This sufficient condition is derived for the class of perturbations that conserve the total mass. It is weaker than existing stability criteria, i.e., it applies to a wider class of flows. Formal stability to infinitesimally small perturbations of arbitrary shape is obtained for two classes of large-scale geophysical flows: pseudo-eastward flow with constant shear, and localized coherent structures of modon type.

Sakuma, H.↗
NASA NTRS1990

Observations of nonlinear effects in directional spectra of shoaling gravity waves

The spatial evolution of a directionally spread wave field on a near-planar natural beach is examined using data from longshore arrays of pressure sensors and wave staffs at depths 10.3 and 4.1 m. High-resolution frequency-directional spectra from the deeper array are used to initialize a linear refraction model, and the resulting model predictions are compared with frequency-directional measurements at the shallow array. Linear theory inaccurately predicts both the shapes of directional spectra in shallow water and the total variances in some frequency bands. The discrepancies are largest for frequencies associated with maxima in the bicoherence spectrum, suggesting the importance of nonlinear effects.

Freilich, M. H.↗
NASA NTRS1990

Barotropic motions and the exchange of angular momentum between the oceans and solid earth

The angular momentum exchange between the earth atmosphere and the solid earth is examined with emphasis placed on the role of the ocean in the momentum transfer. Analysis of external torques such as surface wind stresses and continental torques suggest that, in general, the related angular momentum changes are mostly associated with barotropic variability in the ocean. Solutions for a midlatitude basin obtained with a shallow-water numerical model illustrate how angular momentum in a barotropic ocean is exchanged with the solid earth.

Ponte, Rui M.↗
NASA NTRS1990

Finite-element schemes for extended integrations of atmospheric models

Of the two finite-element models presently used to investigate the effect of the conservation of integral invariants, by means of finite-element discretization schemes of the shallow-water equations, in order to serve as a paradigm of long-term atmospheric-model integrations, the first employs rectangular elements and conserves total energy, while the second uses triangular elements and a high-accuracy two-stage Numerov-Galerkin method. Attention is given to critical times for numerical nonlinear instability, as well as to the determination of the critical degree of dissipation entailed by the achievement of stable long-term integrations. Relative computational efficiency and accuracy comparisons are presented for the two finite-element schemes.

Steppeler, J.↗
NASA NTRS1990

Inverse methods for assessing ship-of-opportunity networks and estimating circulation and winds from tropical expendable bathythermograph data

Inverse methods for estimating the surface ciculation of the equatorial Pacific by combining a linear reduced-gravity shallow-water model with the Tropical Ocean-Global Atmosphere ship-of-opportunity expendable bathythermograph (TOGA SOP XBT) observing program are examined. It is demonstrated that a simple linear model of the upper circulation of the equatorial Pacific can be successfully used as a weak constraint when smoothing the TOGA SOP XBT data. A circulation is sought as the weighted least squares fit to the dynamics and the data. The solution method is an expansion in representer functions, and the generalized inverse problem is thereby reduced from a functional problem to an algebraic problem for the coefficients of the representer. A specific inverse calculation using synthetic forcing and data is presented.

Bennett, Andrew F.↗
NASA NTRS1991

The Madden-Julian oscillation and the angular momentum balance in a barotropic ocean model

The oceanic response to the Madden and Julian (1971, 1972) oscillation (MJO) wind stresses are studied with special attention given to the nature of the related angular momentum exchanges between the ocean and the solid earth for idealized 40- and 50-day fluctuations of Pacific winds. The character of these exchanges is illustrated with the use of numerical solutions of a shallow water ocean model, which were found for a constant depth basin centered on the equator and extending over 140 deg in longitude. Solutions also suggest that even small (0.5-1.5-cm) coastal sea level fluctuations can cause variations in the length of day comparable to observed values in the 40- to 50-day band.

Ponte, Rui M.↗
NASA NTRS1991

Stability of propagating modons for small-amplitude perturbations

A stability analysis based on Arnol'd-Liapunov arguments in a gauge-variable formalism is applied to a generalized form of propagating modons. The method was previously applied to the special case of Stern's modon in a quiescent background flow. The analysis presented here shows that propagating-modon solutions in the shallow-water equations are stable to small-amplitude perturbations, regardless of the sign of their translational speed, as long as this is much smaller in magnitude than the solid-rotation speed of the earth. Sufficient conditions for stability are that the given flow be quasigeostrophic, i.e., that the Rossby number be small, and that the associated Froude number be one order of magnitude smaller than the Rossby number.

Sakuma, H.↗
NASA NTRS1991

Simplification of the Kalman filter for meteorological data assimilation

The paper proposes a new statistical method of data assimilation that is based on a simplification of the Kalman filter equations. The forecast error covariance evolution is approximated simply by advecting the mass-error covariance field, deriving the remaining covariances geostrophically, and accounting for external model-error forcing only at the end of each forecast cycle. This greatly reduces the cost of computation of the forecast error covariance. In simulations with a linear, one-dimensional shallow-water model and data generated artificially, the performance of the simplified filter is compared with that of the Kalman filter and the optimal interpolation (OI) method. The simplified filter produces analyses that are nearly optimal, and represents a significant improvement over OI.

Dee, Dick P.↗
NASA NTRS1991

KSC off-runway contingency operation - Mode 7

The possibility of a mishap during a space shuttle landing at Kennedy Space Center (KSC) dictates the need for plans to rescue astronauts from areas other than the Shuttle Landing Facility (SLF). All shuttle landings are unpowered, gliding flight maneuvers, and a deviation from the planned flight profile could result in a shuttle landing or crashing somewhere other than the SLF runway. The geography of the Kennedy Space Center makes helicopter airlifting the only universal means of transportation for the rescue crew. This rescue crew is composed of KSC contractor fire-rescuemen who would ride to the crash scene on USAF HH-3 helicopters. These crews are provided with personal protective suits and training in shallow water, swamp, and dry land rescues. They aid the egress of the crew to a safe area for helicopter pickup and subsequent triage and medevac.

Maples, Arthur↗
NASA NTRS1992

Orographically forced oscillations in a dynamical model of the Martian atmosphere

The barotropic, orographically-forced intraseasonal oscillations of the Martian atmosphere are presently analyzed by means of a single-layer shallow-water model. An oscillation with 85-Martian day mean period is noted in a time-series of the model global atmospheric angular momentum, and its robustness is verified. The oscillation has a standing zonal component whose centers of action are located upstream and downstream of salient orographic features. A resemblance arises between the oscillation's northern-hemisphere features and those of the terrestrial 40-day oscillation.

Keppenne, Christian L.↗
NASA NTRS1993

A relationship between potential vorticity and zonal wind on Jupiter

We present evidence from analysis of Voyager data and numerical experiments that in Jupiter's troposphere at midlatitudes the potential vorticity is given simply by the reciprocal of the streamfunction. This relationship agrees with the results of a vortex-tube stretching analysis of the Voyager wind-field data of the Great Red Spot and White Oval BC, whereas other published models do not. The derivative of streamfunction with respect to potential vorticity is negative definite, and in the quasigeostrophic limit the relationship is neutrally stable with respect to Arnold's second stability theorem. Numerical experiments indicate that the relationship is also neutrally stable in the primitive shallow-water system. This resolves a long-standing question as to how Jupiter's cloud-top winds are able to violate the Rayleigh-Kuo stability criterion, and constrains the two-layer model to a single free parameter.

Dowling, Timothy E.↗
NASA NTRS1993

Global barotropic response to a tropical forcing

Zonally varying flow has been used to initialize numerical models and has been shown to play an important role in strong localized responses both in extratropics and the tropics. In this study, a climatological 200 mb January mean is used as a steady basic state of a barotropical model which consists of shallow water equations and a mass source centered at 4 deg S/120 deg E to simulate convective heating over Indonesia region. In the experiment, tropical responses appear not only over the western Pacific, where the forcing is located, but also over the eastern Pacific where the response is related to the zonally varying basic state. The westward propagating equatorial Rossby waves excited by the forcing interact with waves out of and into the tropics and the positive and negative phase of the Rossby waves result in blocking circulation over North America and tropical plumes over equatorial eastern Pacific, respectively.

Zhang, Yuxia↗