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At least 163 records · Page 9

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NASA NTRS1975

Initialization procedures for primitive equation models

A linear analysis and comparison of the damping properties of six dynamic initialization schemes is presented, indicating that the Okamura-Rivas scheme has the most efficient damping properties over the whole frequency range, and suggesting that it should be faster than the other methods and given more stable results. The results obtained with a nonlinear shallow water equations model agree well with the linear analysis. The Okamura-Rivas scheme attains complete balance in the equivalent of 5 to 6 hours of leapfrog forecasting, and requires in this model an order of magnitude less computation than the balance equation solution.

Grant, W. K. F.↗

NASA NTRS1976

Evaluation of LANDSAT-2 (ERTS) images applied to geologic structures and mineral resources of South America

The author has identified the following significant results. The Salar of Coposa is located in northern Chile along the frontier with Bolivia. The surface was divided into six general classes of materials. Analysis of LANDSAT image 1243-14001 by use of interactive multispectral computer (Image 100) enabled accurate repetition of these general classes based on reflectance. The Salar of Uyuni is the largest of the South American evaporite deposits. Using image 1243-13595, and parallel piped computer classification of reflectance units, the Salar was divided into nine classes ranging from deep to shallow water, water over salt, salt saturated with water, and several classes of dry salt.

Carter, W. D.↗

NASA NTRS1976

A two-dimensional model for the transport of pollutants in an urban basin

The distribution of an inert chemical species, carbon monoxide (CO), emitted mainly from automobile exhaust is investigated. The transport model, in analogy with the shallow water theory in fluid dynamics, considers variation of all physical quantities in the horizontal direction below the temperature inversion layer. Pollutants are found to be carried primarily by the wind; turbulent diffusion in a normal day plays only a minor role. The concentration of CO predicted by the present model for the entire Los Angeles basin is compared with observed data at nine stations. Accuracy of four different numerical schemes, the effect of turbulent diffusivity, and the source strengths are examined.

Liu, C. Y.↗

NASA NTRS1977

Updating prediction models by dynamical relaxation - An examination of the technique

A dynamical relaxation technique for updating prediction models is analyzed with the help of the linear and nonlinear barotropic primitive equations. It is assumed that a complete four-dimensional time history of some prescribed subset of the meteorological variables is known. The rate of adaptation of the flow variables toward the true state is determined for a linearized f-model, and for mid-latitude and equatorial beta-plane models. The results of the analysis are corroborated by numerical experiments with the nonlinear shallow-water equations.

Davies, H. C.↗

NASA NTRS1978

Lidar: A laser technique for remote sensing

Experimental airborne lidar systems proved to be useful for shallow water bathymetric measurements, and detection and identification of oil slicks and algae. Dye fluorescence applications using organic dyes was studied. The possibility of remotely inducing dye flourescence by means of pulsed lasers opens up several hydrospheric applications for measuring water currents, water temperature, and salinity. Aerosol measurements by lidar are also discussed.

Wilkerson, T. D.↗

NASA NTRS1977

A two-dimensional model for the transport of pollutants in an urban basin

The distribution of carbon monoxide emitted mainly from an automobile exhaust is investigated. Carbon monoxide is assumed to be chemically inert. The transport model, in analogy with the shallow-water theory in fluid dynamics, considers variation of all physical quantities in the horizontal direction below the temperature inversion layer. Pollutants are found to be carried primarily by the wind; turbulent diffusion in a normal day plays only a minor role. The concentration of CO predicted by the present model for the entire Los Angeles basin is compared with observed data at nine stations. Accuracy of four different numerical schemes, the effect of turbulent diffusivity, and the source strengths are examined.

Liu, C. Y.↗

NASA NTRS1978

Experiments on strong interactions between solitary waves

Experiments on the interaction between solitary shallow-water waves propagating in the same direction have been performed in a rectangular channel. Two methods were devised to compensate for the dissipation of the waves in order to compare results with Hirota's (1971) solution for the collision of solitons described by the Korteweg-de Vries equation. Both qualitative and quantitative agreement with theory is obtained using the proposed corrections for wave damping.

Weidman, P. D.↗

NASA NTRS1979

Description and field test of an in situ coliform monitoring system

A prototype in situ system for monitoring the levels of fecal coliforms in shallow water bodies was developed and evaluated. This system was based on the known relationship between the concentration of the coliform bacteria and the amount of hydrogen they produce during growth in a complex organic media. The prototype system consists of a sampler platform, which sits on the bottom; a surface buoy, which transmits sampler-generated data; and a shore station, which receives, displays the data, and controls the sampler. The concept of remote monitoring of fecal coliform concentrations by utilizing a system based on the electrochemical method was verified during the evaluation of the prototype.

Grana, D. C.↗

NASA NTRS1979

On the influence of orography on large-scale atmospheric flow

The steady response to orography as described by shallow-water equations on the sphere is examined in an attempt to provide insight into the dynamical effects of large-scale orographic features on atmospheric motion. The model equations and the zonal flows and orography used in the study are described. The results for simple mountains and for the earth orography are given. The two-dimensional nature of the horizontal propagation on the sphere is emphasized. The results give interesting indications of the regions of influence of mountains and suggest that quantitative theories of the stationary waves must involve a full representation of the spherical domain.

Grose, W. L.↗

NASA NTRS1979

Forced baroclinic ocean motions. III - The linear equatorial basin case

The linear response to simple wind stress of an equatorial ocean described by baroclinic shallow water equations is studied. Three types of basin are considered in treating the linear spin-up of the equatorial ocean: a symmetric basin with zonal walls distant from the equator (compared to the equatorial radius of deformation); a symmetric basin with zonal walls near the equator; and an asymmetric basin with one wall near the equator and one distant. The approach to the steady (Sverdrup) solutions is analyzed, with special attention given to the fast planetary response. Numerical treatments of spin-up for various winds in each type of basin are also presented.

Cane, M. A.↗

NASA NTRS1980

Mountain winds (revisited)

The prediction of extremely high wind speeds, at ground level on the downstream side of a mountain range, is possible by solving the initial value problem for a two-layered nonlinear shallow water model of the atmosphere. Three different numerical methods are described to find the solutions which may involve shocks: (1) the vonNeumann-Richtmyer artificial viscosity method, (2) a filtering scheme, and (3) a hybrid method.

Isaacson, E.↗

NASA NTRS1980

SEASAT-SAR data analysis in the US: An update

A graph is shown which compares SEASAT synthetic aperture radar (SAR) wave length measurements and Krasman's shallow water dispersion relationship for a swell system of deep water length 210 m and period 11.7 sec. The data were taken during the Duck experiment. The status of the production of optically correlated SAR data is given along with a tabulation of both digitally and optically processed SAR image data available to the user community as of Aug. 1979. Results from several SAR workshops are mentioned.

Dunne, J. A.↗

NASA NTRS1980

On time discretizations for spectral methods

New methods are introduced for the time integration of the Fourier and Chebyshev methods of solution for dynamic differential equations. These methods are unconditionally stable, even though no matrix inversions are required. Time steps are chosen by accuracy requirements alone. For the Fourier method both leapfrog and Runge-Kutta methods are considered. For the Chebyshev method only Runge-Kutta schemes are tested. Numerical calculations are presented to verify the analytic results. Applications to the shallow water equations are presented.

Gottlieb, D.↗

NASA NTRS1981

Refraction of coastal ocean waves

Refraction of gravity waves in the coastal area off Cape Hatteras, NC as documented by synthetic aperture radar (SAR) imagery from Seasat orbit 974 (collected on September 3, 1978) is discussed. An analysis of optical Fourier transforms (OFTs) from more than 70 geographical positions yields estimates of wavelength and wave direction for each position. In addition, independent estimates of the same two quantities are calculated using two simple theoretical wave-refraction models. The OFT results are then compared with the theoretical results. A statistical analysis shows a significant degree of linear correlation between the data sets. This is considered to indicate that the Seasat SAR produces imagery whose clarity is sufficient to show the refraction of gravity waves in shallow water.

Shuchman, R. A.↗

NASA NTRS1981

On the computational noise of finite-difference schemes used in ocean models

Different distributions of variables over the horizontal array of grid points in an ocean circulation model are investigated, using the shallow water equations as a guide in the choice of finite-difference schemes for use in ocean modeling. It is shown that the scheme with diffusive dissipation, in which the horizontal velocity is carried at the center and the height field is carried at each corner of a rectangular grid, successively suppresses numerical noise in a coarse (greater than 100 km) grid ocean model. For resolutions smaller than 50 km, it is shown that the scheme in which zonal velocity is carried at points to the east and west of the point of a rectangular grid where the height is carried, with meridional velocity carried to the north and south of the height point, can be free of noise for the gravest mode.

Batteen, M. L.↗

NASA NTRS1981

A simple atmospheric model on the sphere with 100% parallelism

A simple shallow water equations model used to test numerical weather prediction schemes is presented. The spherical geometry is transformed into a formally doubly periodic configuration which can be implemented on a massively parallel computer at 100% parallelism. A nonstaggered grid with all variables defined at the grid points (circles) is used. The parallel structure was simulated by performing step 1 in a FORTRAN array, on an Amdahl serial machine, changing the signs of the winds on the dark side.

Kalnay, E.↗

NASA NTRS1981

The response of a linear baroclinic equatorial ocean to periodic forcing

An investigation is conducted regarding the periodic response of the linear inviscid shallow water equations in a meridionally unbounded basin to zonal forcings at a single low frequency omega. A general solution in the long wave approximation and on an equatorial beta-plane is obtained by summing the Kelvin mode and the finite sum of Rossby modes whose turning points lie equatorward of the turning latitude at frequency omega. The results of the investigation suggest that even if the low frequency forcing has a simple structure, considerable spatial inhomogeneity in the deep ocean response would have to be expected. On the basis of linear inviscid theory, some conclusions are drawn about the causes of the differences between equatorial thermocline response in the Atlantic and Pacific.

Cane, M. A.↗

NASA NTRS1982

Initial conditions and Korteweg-de Vries solitons

The effects of rectangular initial data on the evolution of solitons governed by the Korteweg-de Vries equation is studied. Both isolated and separated disturbances are considered, providing some general insight into how the nature of the initial condition influences the appearance of solitons in the asymptotic state. The analytic approach is based on the inverse scattering transform which relates the initial condition to Schroedinger's equation. The results are used to model the initial shallow-water disturbances, and the results can be summarized by stating that the number of evolved solitons depends on the strength of each rectangular disturbance, the relative amplitudes of the rectangular disturbances, and the relative proximity of the disturbances.

Weidman, P. D.↗