SEARCH · Search NASA

Results for “dynamic processes”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 865 records · Page 48

All sources NASA NTRS DOE OSTI

NASA NTRS1983

Interpretation of MST radar returns from clear air

The nature of the scattering and reflection mechanisms that give rise to the MST radar echoes from the clear air is essential in the correct interpretation of the data about winds, waves, turbulence and stability in the atmosphere. There are two main aspects: the nature of the targets the radar sees and their generation mechanisms; and the signatures of the radar signals returned from the different targets. Volume scatterings from isotropic or anisotropic turbulence, and partial reflections from horizontally stratified, sharp refractive index gradients are believed the main contributors to radar echoes. Combined effects from all the mechanisms probably produce the observed data. The signature of the echo signals for these different scatterers under realistic experimental conditions should be studied. It is hoped from these studies, the nature of the targets can be better understood, and related to atmospheric dynamic processes.

Liu, C. H.↗

NASA NTRS1984

Analysis of the Earth's variable rotation

The objective was to analyze the Earth's rotation, and to compare the observations with the atmospheric and seismic excitation functions. The variation in the Earth's rotation can be separated into the length-of-day (LOD) variation and the polar motion. Possible driving mechanisms include: atmospheric/oceanic circulations, seismic activities, solar-lunar tides, mantle convection, core-mantle coupling, and solar activities. The major problem of concern was the identification of these dynamical processes as primary driving mechanisms for the various features in the variation of the Earth's rotation.

Chao, B. F.↗

NASA NTRS1984

Observational and theoretical studies of the evolving structure of baroclinic waves

Dynamical processes involved in comma cloud formation, and passive tracer evolution in a baroclinic wave are discussed. An analytical solution was obtained demonstrating the complex nongeostrophic flow pattern involved in the redistribution of low level constituents in a finite amplitude baroclinic wave, and in the formation of the typical humidity and cloud distributions in such a wave. Observational and theoretical studies of blocking weather patterns in middle latitude flows were studied. The differences in the energy and enstrophy cascades in blocking and nonblocking situations were shown. It was established that pronounced upscale flow of both of these quantities, from intermediate to planetary scales, occurs during blocking episodes. The upscale flux of enstrophy, in particular, suggests that the persistence of blocking periods may be due to reduced dissipation of the large scale circulation and therefore entail some above normal predictability.

Saltzman, B.↗

NASA NTRS1984

Embedded shear layer computations for increased drag reduction

One of the most promising methods of minimizing drag is the reduction of skin friction by injection of low momentum fluid into the near-wall region of turbulent boundary layer flows. This method could be made more effective by limiting the spread rate of the resulting mixing region. In order to achieve a better understanding of how this goal might be achieved, numerical investigations of the relevant fluid dynamic processes governing these regions have been conducted. A compact finite-difference algorithm has been applied to the complete form of the governing conservation equations for a two-dimensional laminar mixing layer. The ability of this computational approach to model successfully the formation and interaction of the large scale vortical structures which dominate such flow fields is verified in the present study. Parameters which affect the spread rate of the mixing region are also identified. In addition, the relative importance of viscous and momentum transport effects in the vortex interactions is determined.

Gatski, T. B.↗

NASA NTRS1984

Semiannual oscillation of stratospheric ozone

By applying spherical harmonic analysis to the ozone data obtained from the Nimbus-7 solar backscattered UV-radiation measurements for the period from November 1978 to October 1980, the following features of the semi-annual oscillation (SAO) in stratospheric ozone are revealed: (1) the equatorial ozone SAO has a broad maximum of the order of 0.5 (mixing ratio in micro-g/g) between the 10 mb and 3 mb levels, and the maximum shifts downward from 1 mb in June (and December) to 40 mb in November (and May); (2) amplitudes of polar ozone SAO's are larger than that of the equatorial SAO, with a major maximum at 2 mb which is 2 micro-g/g at 75 deg N and 0.8 micro-g/g at 75 deg S, respectively; (3) the inverse phase between the polar and tropical SAO which occurs around the 3 mb (about 40 km) level can be interpreted in terms of the temperature-dependent ozone chemistry and the poleward meridional transport of ozone by dynamical processes in the atmosphere.

Maeda, K.↗

NASA NTRS1984

Mature thunderstorm cloud-top structure and dynamics - A three-dimensional numerical simulation study

The present investigation is concerned with results from an initial set of comparative experiments in a project which utilize a three-dimensional convective storm model. The modeling results presented are related to four comparative experiments, designated Cases A through D. One of two scientific questions considered involves the dynamical processes, either near the cloud top or well within the cloud interior, which contribute to organize cloud thermal patterns such as those revealed by IR satellite imagery for some storms having strong internal cloud-scale rotation. The second question is concerned with differences, in cloud-top height and temperature field characteristics, between thunderstorms with and without significant internal cloud-scale rotation. The four experiments A-D are compared with regard to both interior and cloud-top configurations in the context of the second question. A particular strong-shear experiment, Case B, is analyzed to address question one.

Schlesinger, R. E.↗

NASA NTRS1984

Fracture, failure, and fragmentation

A general approach is required for describing matter of behavior when the failure is likely to involve growth and coalescence of a large number of fractures. Failures of this kind appear frequently in rapid dynamic processes, particularly in the formation of spall fragments. An approach to formulating constitutive relations that accounts for the opening, shear and growth of an ensemble of cracks is discussed. The approach accounts for plastic flow accompanying fragmentation. The resulting constitutive relations were incorporated into a Lagrangian computer program. A theoretical approach to coalescence is described. The simplest formulation uses a linear Liouville equation, with crack growth limited by the mean free path of cracks, assumed constant. This approach allows for an anisotropic distribution of cracks. An alternative approach in which the decrease of the mean free path with increasing crack size is accounted for, but the crack distribution is assumed isotropic is described. A reduction of the governing Liouville equation to an ordinary differential equation of third order is possible, and the result can be used to determine how mean free path decreases with increasing crack size.

Dienes, J. K.↗

NASA NTRS1984

Air-sea heat exchange, an element of the water cycle

The distribution and variation of water vapor, clouds and precipitation are examined. Principal driving forces for these distributions are energy exchange and evaporation at the air-sea interface, which are also important elements of air-sea interaction studies. The overall aim of air-sea interaction studies is to quantitatively determine mass, momentum and energy fluxes, with the goal of understanding the mechanisms controlling them. The results of general circulation simulations indicate that the atmosphere in mid-latitudes responds to changes in the oceanic surface conditions in the tropics. This correlation reflects the strong interaction between tropical and mid-latitude conditions caused by the transport of heat and momentum from the tropics. Studies of air-sea exchanges involve a large number of physica, chemical and dynamical processes including heat flux, radiation, sea-surface temperature, precipitation, winds and ocean currents. The fluxes of latent heat are studied and the potential use of satellite data in determining them evaluated. Alternative ways of inferring heat fluxes will be considered.

Chahine, M. T.↗

NASA NTRS1984

Theoretical Modeling for Numerical Weather Prediction

The goal is to utilize predictability theory and numerical experimentation to identify and understand some of the dynamical processes which must be modeled more realistically if large-scale numerical weather predictions are to be improved. The emphasis is on the use of relatively simple models to exlore the properties of physically comprehensive general circulation models (GCM's). A global linear quasi-geostrophic model and the Goddard Laboratory for Atmospheric Sciences (GLAS) GCM were used to investigate several mechanisms which are responsible for the decay of large-scale forecast skill in mid-latitude numerical weather predictions. Five-day forecasts for an ensemble of cases were made using First GARP Global Experiment data. It was found that forecast skill depends crucially on the specification of the stationary forcing. A lack of stationary forcing leads to spurious westwad propagation of the ultralong waves. Forecasts made with stationary forcings derived from climatological data are superior to those using forcings inferred from observations immediately preceding the forecast period. Interhemispheric forecast differences were analyzed, and the model errors were compared to errors of a simple persistence-damped-to-climatology scheme and to errors of the GLAS GCM.

Somerville, R. C. J.↗

NASA NTRS1982

The Middle Atmosphere Program: Winter In Northern Europe (MAP/WINE)

The goals of map/wind (winter in Northern Europe) are to better understand: (1) the interaction of planetary waves of tropospheric origin; (2) the temporal and spatial development of sudden stratospheric warmings; (3) the temporal and spatial development of mesospheric cooling events in conjunction with stratospheric warmings; (4) the vertical and horizontal transport of minor constituents; (5) the effects on the chemistry of neutral and charged species of the large temperature changes occurring during stratospheric warmings and mesospheric cooling; (6) sources of turbulent energy; (7) the temporal and spatial development of turbulent layers; and (8) the contributions of dynamical processes to the heating and cooling of the mesospheric and turbopause region.

Vonzahn, U.↗

NASA NTRS1985

Studies of Planetary Rings

Dynamic processes in ring structures (spiral density waves; shepherding processes; and erosional transport and global redistribution of ring materials) and planetary ring observations (Jupiter's ring; the nature of the F ring; and the irregular structure of Saturn's B ring) were examined.

Cuzzi, J. N.↗

NASA NTRS1985

Development of algorithms for using satellite meteorological data sets to study global transport of stratospheric aerosols and ozone

The utilization of stratospheric aerosol and ozone measurements obtained from the NASA developed SAM II and SAGE satellite instruments were investigated for their global scale transports. The stratospheric aerosols showed that during the stratospheric warming of the winter 1978 to 1979, the distribution of the zonal mean aerosol extinction ratio in the northern high latitude exhibited distinct changes. Dynamic processes might have played an important role in maintenance role in maintenance of this zonal mean distribution. As to the stratospheric ozone, large poleward ozone transports are shown to occur in the altitude region from 24 km to 38 km near 55N during this warming. This altitude region is shown to be a transition region of the phase relationship between ozone and temperature waves from an in-phase one above 38 km. It is shown that the ozone solar heating in the upper stratosphere might lead to enhancement of the damping rate of the planetary waves due to infrared radiation alone in agreement with theoretical analyses and an earlier observational study.

Want, P. H.↗

NASA NTRS1985

Ephemeral regions versus pseudo ephemeral regions

New studies of the quiet Sun reveal that ephemeral active regions constitute minority rather than a majority of all the short lived, small scale bipolar features on the Sun. In contrast to the recognized patterns of growth and decay of ephemeral regions, various examples of the creation of other temporary bipoles nicknamed pseudo ephemeral regions are illustrated. The pseudo ephemeral regions are the consequence of combinations of small scale dynamic processes of the quiet Sun including: (1) fragmentation of network magnetic fields, (2) the separation of opposite polarity halves of ephemeral regions as they grow and evolve, and (3) the coalescence of weak network or intranetwork magnetic fields. New observations offer the possibility of resolving the discrepancies that have arisen in the association of ephemeral regions with X-ray bright points. Many X-ray bright points may be related to those pseudo ephemeral regions which have begun to exhibit magnetic flux loss.

Martin, S. F.↗

NASA NTRS1984

Analysis of stress-strain relationships in silicon ribbon

An analysis of stress-strain relationships in silicon ribbon is presented. A model to present entire process, dynamical Transit Analysis is developed. It is found that knowledge of past-strain history is significant in modeling activities.

Dillon, O. W., Jr.↗

NASA NTRS1985

Late-stage planetesimals: How big?

Numerical simulation of the early stages of planet growth show that a few bodies nearly 1000 km in diameter may have formed within approx. 100,000 yr after solid material grew into km scale planetesimals by gravitational instability. Even after such large bodies formed, the bulk of the mass of the future terrestrial planet zone resided in small bodies. Subsequent evolution is difficult to model because it requires simultaneous consideration of continuum (multitudinous small bodies) and discrete (a few large bodies) evolution. Some relevant issues include definition of accretional feeding zones, evaluation of the range of gravitational influence, viscous transport and diffusion, orbital commensurabilities, role of gas, etc. The first large bodies may have been (1) the embryos of the final planets, which grew by accreting tiny planetesimals, or (2) merely the first of many 1000+ km bodies, which grew independently and later collided to form the planets. Models of late stage accretion that assume all bodies to be initially nearly Moon sized provide insight into relevant collisional and dynamical processes. The chief point in this research is that the correct size distribution during the later stages of planet growth remains unknown.

Greenberg, R.↗

NASA NTRS1984

Supermassive monopole stars

In this paper, the evolution of a superheavy monopole-dominated universe is reexamined; in particular, the evolution of rotation-stabilized monopole-burning 'stars', balancing effects of radiation and annihilation are examined. In contrast to earlier results, it is found that this can lead to complete burning of all poles present in such an object within finite time. If monopoles can be brought within acceptable limits by dynamical processes, an inflationary epoch of the early universe need not be associated with grand unification.

Fry, J. N.↗

NASA NTRS1984

The global distribution and variability of stratospheric constituents measured by LIMS

The purpose of the Nimbus 7 LIMS experiment was to sound the composition and structure of the upper atmosphere and provide data for study of photochemistry, radiation, and dynamics processes. Vertical profiles were measured of temperature and ozone (O3) over the 10-km to 65-km range and water vapor, nitrogen dioxide, and nitric acid over the 10-km to 50-km range. Latitude coverage extended from 64 deg S to 84 deg N. Several general features of the atmosphere have emerged from data analyzes thus far. Nitrogen dioxide exhibits rapid latitudinal variations in winter and shows hemispheric asymmetry with generally higher vertical column amount in the summer hemisphere. HNO3 data show that this gas is highly variable with altitude, latitude, and season. Smallest mixing ratios occur in the tropics, and the largest values occur in the high latitude winter hemisphere. The results show that O3, NO2, and HNO3 are strongly affected during a stratospheric warming.

Russell, J. M., III↗

NASA NTRS1983

Dual Doppler lidar measurements of winds in the JAWS experiment

Differences are noted in the operations of Doppler lidar and radar for the case of a thunderstorm outflow observed during the Joint Airport Weather Studies project field experiments. Calculated wind fields agreed with surface wind observations made routinely by the Portable Automated Mesonet stations. The lidar data are found to complement Doppler radar observations; while the latter is superior for the measurement of wind fields within convective storms, the former is more useful in examinations of dynamical processes in regions outside storm.

Rothermel, J.↗