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At least 397 records · Page 22

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NASA NTRS1986

Vertical structure of the wind field during the Special Observing Period I of the Global Weather Experiment

The vertical structure of the global atmosphere is analyzed for selected periods of the Special Observing Period I (SOP-I) for the Global Weather Experiment (GWE). The analysis consists of projection of the stream-function and velocity potential at 200 and 850 mb on spherical harmonics and of the wind and height fields on the normal modes of a linearized form of the primitive equations for a basic state at rest. The kinematic vertical structure is discussed in terms of correlation coefficients of the 200 mb and 850 mb winds and analysis of the internal and external normal modes of the primitive equations. The reliability of the results is checked by applying the same analysis methods to data sets obtained from three different institutions: Geophysical Fluid Dynamics Laboratory (GFDL), European Center for Medium Range Weather Forecasting (ECMWF), and Goddard Laboratory for the Atmospheres (GLA). It is found that, on a global basis, vertically reversing circulations are as important as the equivalent barotropic structures. For the verticaly reversing components, the gravity and mixed Rossby-gravity modes have contributions of the same order of magnitude as those of the Rossby modes in tropical latitudes.

Paegle, J. N.↗

NASA NTRS1987

Rate limits in silicon sheet growth - The connections between vertical and horizontal methods

Meniscus-defined techniques for the growth of thin silicon sheets fall into two categories: vertical and horizontal growth. The interactions of the temperature field and the crystal shape are analyzed for both methods using two-dimensional finite-element models which include heat transfer and capillarity. Heat transfer in vertical growth systems is dominated by conduction in the melt and the crystal, with almost flat melt/crystal interfaces that are perpendicular to the direction of growth. The high axial temperature gradients characteristic of vertical growth lead to high thermal stresses. The maximum growth rate is also limited by capillarity which can restrict the conduction of heat from the melt into the crystal. In horizontal growth the melt/crystal interface stretches across the surface of the melt pool many times the crystal thickness, and low growth rates are achievable with careful temperature control. With a moderate axial temperature gradient in the sheet a substantial portion of the latent heat conducts along the sheet and the surface of the melt pool becomes supercooled, leading to dendritic growth. The thermal supercooling is surpressed by lowering the axial gradient in the crystal; this configuration is the most desirable for the growth of high quality crystals. An expression derived from scaling analysis relating the growth rate and the crucible temperature is shown to be reliable for horizontal growth.

Thomas, Paul D.↗

NASA NTRS1987

Vertical O(sub 3) distribution as a diagnostic for eddy diffusion profile

A model study of the distribution of ozone on Mars is presented. It is showed that knowledge of the vertical ozone distribution, such as could be obtained from ultraviolet measurements from an orbiter, could be used to infer vertical transport rates at various levels in the atmosphere. The dependence of the vertical distribution of O(sub 3) on the height variation of eddy diffusion coefficient is illustrated. Ozone abundance is a valuable diagnostic for other climatological parameters. In addition, the sensitivity of O(sub 3) distribution to eddy diffusion may aid in determining the role of surface oxidation and recombination processes and lead to a better understanding of the volatiles released or adsorbed cyclically in the Martian regolith.

Tyler, A. L.↗

NASA NTRS1988

Convective flows in enclosures with vertical temperature or concentration gradients

The transport process in the fluid phase during the growth of a crystal has a profound influence on the structure and quality of the solid phase. In vertical growth techniques the fluid phase is often subjected to vertical temperature and concentration gradients. The main objective is to obtain more experimental data on convective flows in enclosures with vertical temperature or concentration gradients. Among actual crystal systems the parameters vary widely. The parametric ranges studied for mass transfer are mainly dictated by the electrochemical system employed to impose concentration gradients. Temperature or concentration difference are maintained between two horizontal end walls. The other walls are kept insulated. Experimental measurements and observations were made of the heat transfer or mass transfer, flow patterns, and the mean and fluctuating temperature distribution. The method used to visualize the flow pattern in the thermal cases is an electrochemical pH-indicator method. Laser shadowgraphs are employed to visualize flow patterns in the solutal cases.

Wang, L. W.↗

NASA NTRS1989

Measurements of vertical motions by the Saskatoon MF radar (1983-1985): Relationships with horizontal winds and gravity waves

The continuing series of horizontal wind measurements by the spaced-antenna real time winds (RTW) method was supplemented by a phase coherent system for two years. Vertical motions are inferred from the complex autocorrelation functions, and an RTW system provides 5 min samples from 60 to 110 km. Comparisons with full interferometric 3-D velocity measurements confirm the validity of this approach. Following comparisons and corrections with the horizontal winds, mean summer and winter (24 h) days of vertical motions are shown. Tidal fluctuations are evident. In summer the motions are downward, consistent with data from Poker Flat, and the suggestion of Coy et al. (1986) that these represent Eulerian motions. The expected upward Lagrangian motion then results from adding up upward Stokes' drift. The winter motions are more complex, and are discussed in the context of gravity wave fluxes and possible meridional cells. The divergence of the vertical flux of zonal momentum is also calculated and found to be similar to the coriolis torque due to the meridional winds.

Manson, A. H.↗

NASA NTRS1989

Convective flows in enclosures with vertical temperature or concentration gradients

Wang, L. W.↗

NASA NTRS1989

Consistent vertical and horizontal resolution

Simple physical relations (namely, the Rossby ratio between vertical and horizontal scales in quasi-geostrophic flow and the dispersion relation for internal gravity waves) are used to estimate the vertical resolution consistent with a given horizontal resolution. Using these relations it is found that virtually all large scale models and observing systems have inadequate vertical resolution. In models, the excess horizontal resolution can lead to increased model 'noise' rather than improved accuracy. In observing systems, the finer horizontal scales can be severely misrepresented.

Lindzen, Richard S.↗

NASA NTRS1990

Coupling of horizontal, vertical, and temporal resolving power of a satellite temperature sounder

This paper examines the interconnection between the vertical, horizontal, and temporal resolving power of satellite temperature-sounding system. Using a temperature cross section produced by interpolating a set of RAOBs taken at three locations in Texas; Shreveport, Louisiana; Jackson, Mississippi; and Montgomery, Alabama, and an artificially constructed temperature cross section, it was found that the horizontal and temporal resolving power are subject to strong controls imposed by the vertical resolving power of the sounder. Thus, to improve the horizontal or temporal resolving power it is necessary to improve the vertical resolving power' of the satellite instrument itself, or to extend the a priori external information to include correct horizontal and temporal structure.

Thompson, Owen E.↗

NASA NTRS1990

Preliminary design of a supersonic Short-Takeoff and Vertical-Landing (STOVL) fighter aircraft

A preliminary study of a supersonic short takeoff and vertical landing (STOVL) fighter is presented. Three configurations (a lift plus lift/cruise concept, a hybrid fan vectored thrust concept, and a mixed flow vectored thrust concept) were initially investigated with one configuration selected for further design analysis. The selected configuration, the lift plus lift/cruise concept, was successfully integrated to accommodate the powered lift short takeoff and vertical landing requirements as well as the demanding supersonic cruise and point performance requirements. A supersonic fighter aircraft with a short takeoff and vertical landing capability using the lift plus lift/cruise engine concept seems a viable option for the next generation fighter.

Source record↗

NASA NTRS1990

Vertical velocities and momentum fluxes derived from wind measurements in the dusk auroral oval

Results are presented on a chemical release experiment carried out on March 20, 1985 in connection with NASA's Cooperative Observations of Polar Electrodynamics I campaign. Simultaneous neutral wind measurements in E region were carried out at three separate locations over a triangular region with sides of about 150 km in the dusk auroral oval, and the three wind profiles were used to calculate values of divergence and vorticity over the area. The vertical velocity over the hight range was calculated using the mass continuity equation, and the instantaneous vertical momentum fluxes in the E region were derived using the combination of horizontal-wind measurements and calculated vertical velocities. Results show that there is strong coupling between layers in the E region and that the momentum-flux-induced accelerations are at least comparable in magnitude to the pressure gradient and Coriolis force accelerations.

Larsen, M. F.↗

NASA NTRS1991

Horizontal stress in planetary lithospheres from vertical processes

Understanding the stress states in a lithosphere is of fundamental importance for planetary geophysics. It is closely linked to the processes which form and modify tectonic features on the surface and reflects the behavior of the planet's interior, providing a constraint for the difficult problem of determining interior structure and processes. The tectonics on many extraterrestrial bodies (Moon, Mars, and most of the outer planet satellites) appears to be mostly vertical, and the horizontal stresses induced by vertical motions and loads are expected to dominate the deformation of their lithospheres. Herein, only changes are examined in the state of stress induced by processes such as sedimentary and volcanic deposition, erosional denudation, and changes in the thermal gradient that induce uplift or subsidence. This analysis is important both for evaluating stresses for specific regions in which the vertical stress history can be estimated, as well as for applying the proper loading conditions to global stress models. All references to lithosphere herein should be understood to refer to the elastic lithosphere, that layer which deforms elastically or brittlely when subjected to geologically scaled stresses.

Banerdt, W. B.↗

NASA NTRS1991

Static internal performance of ventral and rear nozzle concepts for short-takeoff and vertical-landing aircraft

The internal performance of two exhaust system concepts applicable to single-engine short-take-off and vertical-landing tactical fighter configurations was investigated. These concepts involved blocking (or partially blocking) tailpipe flow to the rear (cruise) nozzle and diverting it through an opening to a ventral nozzle exit for vertical thrust. A set of variable angle vanes at the ventral nozzle exit were used to vary ventral nozzle thrust angle between 45 and 110 deg relative to the positive axial force direction. In the vertical flight mode the rear nozzle (or tailpipe flow to it) was completely blocked. In the transition flight mode flow in the tailpipe was split between the rear and ventral nozzles and the flow was vectored at both exits for aircraft control purposes through this flight regime. In the cruise flight mode the ventral nozzle was sealed and all flow exited through the rear nozzle.

Re, Richard J.↗

NASA NTRS1990

Precipitating cloud vertical structure derived from passive microwave radiometry

A procedure for the retrieval of cloud vertical structure from passive microwave radiometry is demonstrated by using passive microwave radiometry observations made during the Tropical Rainfall Measuring Mission. The procedure uses a set of cloud radiative models, with each model consisting of five vertical layers, specifying a distinct cloud vertical structure in terms of the near-surface parameters. The retrieval procedure is separated into two tasks (1) retrieving a set of geophysical parameters for each cloud radiative model and (2) finding which of the cloud radiative models and its associated retrieved parameters best fit the observed geophysical conditions. It is shown that this retrieval technique can detect differences and similarities between precipitating systems.

Kummerow, Christian D.↗

NASA NTRS1993

A new method to simulate vertical and horizontal structure in galactic disks

We have modified the particles in an N-body treecode to have different softening lengths in the horizontal and vertical directions. This allows us to simultaneously have thin enough particles to resolve the vertical structure in galactic disks, and horizontally large enough particles to suppress the vertical heating due to two-body effects.

Dalcanton, Julianne J.↗

NASA NTRS1993

A mesoscale gravity-wave event observed during CCOPE. IV - Stability analysis and Doppler-derived wave vertical structure

A summary of the results of a detailed study of the vertical structure of mesoscale gravity waves conducted during the Cooperative Convective Precipitation Experiment (CCOPE) is presented. Pressure perturbation fields derived from the Doppler wind fields are compared with the vertical structure of eigenfunctions resulting from a solution to the Taylor-Goldstein linear wave equation for an atmosphere whose mean state is described by vertical profiles obtained from a representative CCOPE sounding. An analysis of the potential for shear instability is also performed on all of the soundings taken on this day to assess the representativeness of the one chosen for the linear theoretical analysis.

Koch, Steven E.↗

NASA NTRS1940

Notes on the stalling of vertical tail surfaces and on fin design

A discussion is given of the important aspects of the stalling of vertical tail surfaces. The type of instability encountered is described and the possibilities of inadvertent occurrence are noted. The influence of directional flight tests on the behavior of a airplane when the tail stall takes place is discussed. In this connection, flight tests of a twin-engine airplane in which the vertical fin area was increased are cited. The reasons for inadequate directional stability in certain modern designs are accounted for and the properties and applications of dorsal fins are discussed. In addition, the chief factors regulating the requirements for conventional area are given, in which connection simplified criterion for directional stability is presented. It may be concluded that the stalling of vertical tail surfaces is not in itself a dangerous condition. Provided sufficient directional stability exists at large angles of sideslip, the tail stall may occur with modern airplanes, as with those of the past, without the knowledge or concern to the pilot.

Thompson, F L↗

NASA NTRS1956

Effects of vertical fins near the nose of the fuselage on the directional and damping-in-yaw stability derivatives of an airplane model under steady-state and oscillatory conditions

A wind-tunnel investigation has been made at low speed to determine the effects of vertical fins placed ahead of the vertical tail on the directional stability and damping-in-yaw characteristics of a swept-wing model under steady-state oscillatory conditions. Various sizes of fins were used above and below the fuselage center line. The vertical-tail size also was varied.

STABILITY, DIRECTIONAL - STATIC↗

NASA NTRS1953

Wind-tunnel investigation of the effects of various dorsal-fin and vertical-tail configurations on the directional stability of a streamlined body at transonic speeds : transonic-bump method

Yawing-moment coefficients were obtained for several dorsal-fin and vertical-tail configurations in combination with a streamlined body through a large angle-of-sideslip range and a Mach number range of 0.59 to 1.11. The results indicated that dorsal fins improved the directional stability characteristics of the body alone and the body-vertical-tail configuration. A ring tail was more effective at small angles of sideslip and less effective at large angles of sideslip than a tapered low-aspect-ratio vertical tail.

TAIL-BODY COMBINATIONS - MISSILES↗