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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 55 records · Page 3
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NASA NTRS1983

A compressible model for the simulation of moist mountain waves

A two-dimensional, nonlinear, nonhydrostatic model is described which allows the calculation of moist airflow in mountainous terrain. The model is compressible, uses a terrain-following coordinate system, and employs lateral and upper boundary conditions which minimize wave reflections. The model's accuracy and sensitivity are examined. These tests suggest that in numerical simulations of vertically propagating, highly nonlinear mountain waves, a wave absorbing layer does not accurately mimic the effects of wave breakdown and dissipation at high levels in the atmosphere. In order to obtain a correct simulation, the region in which the waves are physically absorbed must generally be included in the computational domain (a nonreflective upper boundary condition should be used as well). The utility of the model is demonstrated in two examples (linear waves in a uniform atmosphere and the Jan. 11, 1972 Boulder windstorm) which illustrate how the presence of moisture can influence propagating waves. In both cases, the addition of moisture to the upstream flow greatly reduces the wave response.

Durran, D. R.↗
NASA NTRS1984

Relaxation and free modes of a self-gravitating planet

The relaxation and purely radial free modes of a planet subject to a nonhydrostatic prestress caused by gravity and evidenced by the presence of high mountain ranges and deep abyssal plains are studied. It is shown that there is an infinite set of rheological models of the same type for the planet which have the same relaxation time. Additional information on the behavior of the material is needed to better specify the model. The prestress is shown to shift the period of each purely radial free mode of the planet.

Caputo, M.↗
NASA NTRS1985

Why do we need detailed gravity over continents: Some Australian examples

Geophysical quantities available over a continent are gravity and components of the magnetic field. Direct inferences on crustal structure are difficult to make and strongly dependent on mechanical assumptions the isostatic state. The data for Australia represents one of the best continental scale gravity surveys. The gravity anomalies are generally bland over the continent which confirms that stress relaxation and erosion and rebound were instrumental in reducing nonhydrostatic stresses. In central Australia very large gravity anomalies occur and the region is out of isostatic equilibrium despite the fact that tectonic activity ceased 300 ma ago. The isostatic response functions points to a substantial horizontal compression in the crust. Similar conclusions are drawn for the large anomalies in western Australia. The tectonic implications of these anomalies are examined. In eastern Australia the gravity anomalies are explained in terms of a model of erosion of the highlands and concomitant regional isostatic rebound.

Lambeck, K.↗
NASA NTRS1985

The perturbed neutral circulation in the vicinity of a symmetric stable auroral arc

In the present investigation, a sophisticated high-resolution time-dependent numerical model is used to study the neutral response to changes in the E region electrodynamical forcing and particle heating associated with the appearance of a stable auroral arc. The initial condition is a nighttime ionosphere in the presence of a background precipitation of electrons associated with diffuse auroras. A simulation study is conducted of the perturbation in the neutral circulation. The simulations were performed on the basis of a model which describes nonlinear, nonhydrostatic viscous flow on a rotating atmosphere.

Walterscheid, R. L.↗
NASA NTRS1985

The penetration of mountain waves into the middle atmosphere

A linear nonhydrostatic model of gravity waves forced by a bell-shaped ridge is used to investigate the penetration of mountain waves into the stratosphere and mesosphere during winter and fall. Gravity waves with horizontal scales less than 30 km are found to be trapped near the tropopause and the stratopause in regions of strong winds. The effect of trapping these modes produces a disturbance whose structure broadens with height. In the mesosphere the disturbance appears 20-40 km downstream from the forcing depending on the strength of the intervening winds. Wavebreaking associated with the mountain wave is predicted in the lower stratosphere as a result of wave superposition; no individual harmonic reaches breaking amplitude. In the mesosphere, wave breakdown is more prevalent, and the disturbance spectrum is relatively more monochromatic as a result of the filtering of the shorter scale modes by the lower atmosphere.

Schoeberl, M. R.↗
NASA NTRS1986

Hydrostatic compression of Fe(1-x)O wuestite

Hydrostatic compression measurements on Fe(0.95)O wuestite up to 12 GPa yield a room temperature value for the isothermal bulk modulus of K(ot) = 157 (+ or - 10) GPa at zero pressure. This result is in accord with previous hydrostatic and nonhydrostatic measurements of K(ot) for wuestites of composition: 0.89 = Fe/O 0.95. Dynamic measurements of the bulk modulus by ultrasonic, shock-wave and neutron-scattering experiments tend to yield a larger value: K(ot) approximately 180 GPa. The discrepancy between static and dynamic values cannot be explained by the variation of K(ot) with composition, as has been proposed. This conclusion is based on high-precision compression data and on theoretical models of the effects of defects on elastic constants. Barring serious errors in the published measurements, the available data suggest that wuestite exhibits a volume relaxation under pressure.

Jeanloz, R.↗
NASA NTRS1987

The terminal area simulation system. Volume 1: Theoretical formulation

A three-dimensional numerical cloud model was developed for the general purpose of studying convective phenomena. The model utilizes a time splitting integration procedure in the numerical solution of the compressible nonhydrostatic primitive equations. Turbulence closure is achieved by a conventional first-order diagnostic approximation. Open lateral boundaries are incorporated which minimize wave reflection and which do not induce domain-wide mass trends. Microphysical processes are governed by prognostic equations for potential temperature water vapor, cloud droplets, ice crystals, rain, snow, and hail. Microphysical interactions are computed by numerous Orville-type parameterizations. A diagnostic surface boundary layer is parameterized assuming Monin-Obukhov similarity theory. The governing equation set is approximated on a staggered three-dimensional grid with quadratic-conservative central space differencing. Time differencing is approximated by the second-order Adams-Bashforth method. The vertical grid spacing may be either linear or stretched. The model domain may translate along with a convective cell, even at variable speeds.

Proctor, F. H.↗
NASA NTRS1987

Analysis and simulations of a troposphere-stratosphere gravity wave model. I

An analytical model is presented that accommodates nonhydrostatic shearing stratified flow over an obstacle, and that can be modified to include a superposed stratosphere with constant wind and higher stability. A simulation code is used in parallel with the analytic calculations to demonstrate a methodology for determining the wavelength and magnitude of gravity wave energy reflected, and that transmitted, by the tropopause.

Wurtele, M. G.↗
NASA NTRS1988

The theory of the earth's orientation, with some new results for nutation

The rotation of the earth is variable at a number of time scales, from a few days to thousands of years and longer. Variations occur in the rotation rate, in the geographical position of the rotation axis (referred to as polar motion), and in the position of the axis relative to inertial space (referred to as nutation and precession). The interpretations of the various observations have implications for the dynamical behavior and structure of the earth's deep interior, and for various aspects of meteorology and oceanography. These are reviewed below. A model of the diurnal resonance in nutation for a nonhydrostatically pre-stressed earth is also presented.

Wahr, John M.↗
NASA NTRS1988

Numerical simulation of the 2 August 1985 DFW microburst with the three-dimensional Terminal Area Simulation System

A model simulation is performed for a small, intense thunderstorm which occurred at the Dallas-Fort Worth airport on August 2, 1985, leading to the crash of a commercial jetliner. The simulation is conducted with the three-dimensional Terminal Area Simulation System, a nonhydrostatic cloud model. The simulation is in good agreement with observations of the storm. It is found that for similar events, very little warning time may be possible as warning is based only on the surface level winds.

Proctor, Fred H.↗
NASA NTRS1988

A mesoscale gravity wave event observed during CCOPE. II - Interactions between mesoscale convective systems and the antecedent waves

The interactions between preexisting gravity waves and convective systems were investigated using data obtained by the Cooperative Convection Precipitation Experiment observational network in Montana on July 11-12, 1981. The results indicate that strong convection substantially affects gravity waves locally by augmenting the wave amplitude, reducing its wavelength, distorting the wave shape, altering the wave phase velocity, and greatly weakening the in-phase covariance between the perturbation wind and pressure fields. These convective effects upon gravity waves are explained in terms of hydrostatic and nonhydrostatic pressure forces and gust front processes associated with thunderstorms.

Koch, Steven E.↗
NASA NTRS1989

An ice-water saturation adjustment

A reasonably accurate and noniterative saturation adjustment scheme is proposed to calculate: (1) the amount of condensation and/or deposition necessary to remove any supersaturated vapor, or (2) the amount of evaporation and/or sublimation necessary to remove any subsaturation in the presence of cloud droplets and/or cloud ice. This proposed scheme can be implemented for a nonhydrostatic cloud model. The derivation of the scheme, an evaluation of its performance, and tests for sensitivity to variations in a few key parameters are presented.

Tao, Wei-Kuo↗
NASA NTRS1989

More about the moment of inertia of Mars

Differences between Mars and other terrestrial planets are discussed. Unlike other terrestrial planets, Mars has two nonhydrostatic components of moments of inertia that are nearly equal. The most probable value of I/MR-squared is slightly less than 0.3650.

Kaula, William M.↗
NASA NTRS1990

Theoretical and experimental studies of baroclinic processes

The geophysical fluid flow simulation code, GEOSIM, is being used to study the phenomenon of vacillation in the baroclinic annulus. Having verified that the code predicts vacillation for the same points as the experiments, the work is aiming toward explaining the mechanics of vacillation and pointing out some of the sensitivities of the results to the numerical method. Researchers are finding that there is a structural change associated with amplitude vacillation, where the structural changes are in the vertical. The results disagree with the premise of Lindzen et al, that the vacillation is due to constructive and destructive interference of neutral modes with different phase speeds. The researchers are continuing to study the Spacelab 3 Geophysical Fluid Flow Cell (GFFC) results with horizontal temperature gradients and heating from below. GEOSIM has been used to compute a wide range of cases, and these are being compared with the observations. The computations and observations compare well, and the model is being used to extend the results beyond cases studied in the experiments and to study the mechanics and predictability of the flows. The study of fully nonlinear baroclinic instability using the GFFC apparatus is proceeding with the numerical code. While the first instability that occurs is of planetary scale, secondary instabilities consisting of small-scale, penetrative convection occurs where cold fluid flows over a warm surface. The simultaneous modeling of the planetary scale and the convective scale is possible because of the nonhydrostatic formulation of the model. Some of these results have been animated on the Stardent computer, which shows the explosive nature of the small-scale convection.

Miller, Tim↗
NASA NTRS1990

An algorithm to estimate the heating budget from vertical hydrometeor profiles

A simple algorithm to estimate the latent heating of cloud systems from their vertical hydrometeor profiles is proposed. The derivation as well as the validation of the algorithm is based on output generated by a nonhydrostatic cloud model with parameterized microphysical processes. Mature and decaying stages of a GATE squall-type convective system have been tested. The algorithm-derived heating budget is in reasonable agreement with the budget predicted by the cloud model. The input to the proposed algoritm can be obtained from either a rain retrieval technique based on information from multichannel passive microwave signals or a kinematic cloud model based on information from Doppler radar wind fields and radar reflectivity patterns. Such an application would have significant implications for spaceborne remote sensing and the large-scale weather prediction data assimilation problem.

Tao, Wei-Kuo↗
NASA NTRS1991

Numerical simulation of a subtropical squall line over the Taiwan Strait

The present 2D nonhydrostatic, time-dependent numerical cloud model, which is applied to the structure and development of a subtropical squall line observed during the Taiwan Area Mesoscale Experiment, includes (1) a parameterized ice-phase microphysical scheme, (2) longwave and shortwave radiative-transfer processes, and (3) heat and moisture fluxes from the ocean surface. A comparative study is made of the vertical transport of horizontal momentum and of the latent heat release by the simulated subtropical squall system, as well as the heat release of squall systems occurring in other geographic locations.

Tao, Wei-Kuo↗
NASA NTRS1992

Alexandrite as a high-temperature pressure calibrant, and implications for the ruby-fluorescence scale

The wavelength shifts of the R1 and R2 fluorescence lines of alexandrite (BeAl2O4:Cr(+3)) have been experimentally calibrated against the ruby-fluorescence scale as a function of both hydrostatic and nonhydrostatic pressures between 0 and 50 GPa, and simultaneously as a function of temperatures between 290 and 550 K. It is found that the pressure-temperature cross derivative of the fluorescence wavelength shifts are negligible for both ruby and alexandrite.

Jahren, A. H.↗
NASA NTRS1992

Finite amplitude gravity waves in the Venus atmosphere generated by surface topography

A two-dimensional, fully nonlinear, nonhydrostatic, gravity wave model is used to study the evolution of gravity waves generated near the surface of Venus. The model extends from near the surface to well above the cloud layers. Waves are forced by applying a vertical wind at the bottom boundary. The boundary vertical wind is determined by the product of the horizontal wind and the gradient of the surface height. When wave amplitudes are small, the near-surface horizontal wind is the zonally averaged basic-state zonal wind, and the length scales of the forcing that results are characteristic of the surface height variation. When the forcing becomes larger and wave amplitudes affect the near-surface horizontal wind field, the forcing spectrum becomes more complicated, and a spectrum of waves is generated that is not a direct reflection of the spectrum of the surface height variation. Model spatial resolution required depends on the amplitude of forcing; for very nonlinear cases considered, vertical resolution was 250 m, and horizontal resolution was slightly greater than 1 km. For smaller forcing amplitudes, spatial resolution was much coarser, being 1 km in the vertical and about 10 km in the horizontal. Background static stability and mean wind are typical of those observed in the Venus atmosphere.

Young, R. E.↗