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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

The 4-5 day mode oscillation in zonal winds of Indian middle atmosphere during MONEX-79

In the early studies based on time series of balloon observations, the existence of 4 to 5 day period waves and 10 to 20 day wind fluctuations were found in the tropical lower stratosphere, and they are identified theoretically as the mixed Rossby-gravity wave and the Kelvin wave, respectively. On the basis of these studies, it was established that the vertically propagating equatorial waves play an important role in producing the QBO (quasi-biennial oscillation) in the mean zonal wind through the mechanism of wave-zonal interaction. These studies are mainly concentrated over the equatorial Pacific and Atlantic Oceans. Similar prominent wave disturbances have been observed over the region east of the Indian Ocean during a quasi-biennial oscillation. Zonal winds in upper troposphere and lower stratosphere (10 to 20) km of the middle atmosphere over the Indian subcontinent may bear association with the activity of summer monsoon (June-September). Monsoon Experiment (MONEX-79) has provided upper air observations at Balasore (21 deg. 30 min.N; 85 deg. 56 min.E), during the peak of monsoon months July and August. A unique opportunity has, therefore, been provided to study the normal oscillations present in the zonal winds of lower middle atmosphere over India, which may have implication on large scale wave dynamics. This aspect is examined in the present study.

Reddy, R. S.↗
NASA NTRS2018

Precursors of Magnetic Flux Emergence in the Moat Flows of Active Region AR12673

We report on observations of magnetic disturbances in active region AR12673 between 1 and 3 September 2017 seen as a disruption of the moat flow several hours before the onset of strong flux emergence near the main sunspot. The moat flow is commonly known as a radially oriented strong outflow of photospheric plasma surrounding sunspots, which ends abruptly and thus shapes an annular pattern around the penumbra. Using highly accurate methods of tracking this photospheric flow applied to Solar Dynamics Observatory/Helioseismic and Magnetic Imager data, we are able to describe the evolution of the moat surrounding the main sunspot of AR 12673. We find that several hours before the emergence of strong magnetic flux near the main sunspot, the moat boundaries are broken at these very same locations. This behavior is observed both on 1 and 3 September. There is no such behavior observed in the absence of flux emergence. These observational results pose the question of how often they occur in other active regions and whether the disruption of the moat flow might be, like in this case, an indication of impending enhanced magnetic activity or simply a coincidental event.

Attie, R.↗
NASA NTRS1981

Investigation of MAGSAT and TRIAD magnetometer data to provide corrective information on high-latitude external fields

The compilation of a catalog of the MAGSAT-observed high altitude disturbances is discussed and an example of contents and format is given. The graphs allow the investigation of Birkeland current signatures which are superimposed upon the main geomagnetic field. An example of a display of the MAGSAT orbital tracks in a polar geomagnetic coordinate system with the locations, flow directions, and intensities of field aligned currents shown in color is also given. The display was generated using an interactive color graphics terminal.

Potemra, T. A.↗
NASA NTRS1982

Supervision of dynamic systems: Monitoring, decision-making and control

Effects of task variables on the performance of the human supervisor by means of modelling techniques are discussed. The task variables considered are: The dynamics of the system, the task to be performed, the environmental disturbances and the observation noise. A relationship between task variables and parameters of a supervisory model is assumed. The model consists of three parts: (1) The observer part is thought to be a full order optimal observer, (2) the decision-making part is stated as a set of decision rules, and (3) the controller part is given by a control law. The observer part generates, on the basis of the system output and the control actions, an estimate of the state of the system and its associated variance. The outputs of the observer part are then used by the decision-making part to determine the instants in time of the observation actions on the one hand and the controls actions on the other. The controller part makes use of the estimated state to derive the amplitude(s) of the control action(s).

White, T. N.↗
NASA NTRS1982

Propagation of wide bandwidth signals through strongly turbulent ionized media

Analytic and numerical techniques are presented which directly address the problem of propagation of wide bandwidth signals through random ionized media. This work is applicable to the problems of satellite communication and space based radar observation through a disturbed ionospheric propagation channel that would result from a high altitude chemical release or nuclear detonation. An analytic solution is presented for the two-position, two-frequency mutual coherence function for spherical wave propagation in the strong scattering limit. This solution is used to derive simple expressions for the power impulse response function and to determine its relationship to the important parameters of decorrelation distance and coherence bandwidth which describe the disturbed propagation channel. Results for mean time delay and time delay jitter are presented and compared to direct simulation results and to other theoretical calculations. A numerical/analytical solution to the parabolic wave equation is presented in the form of a multiple phase-screen (MPS) propagation simulation. In this very general solution technique, the random medium is divided into a finite number of layers. The field fluctuation through each layer is obtained by replacing the layer by a centrally located thin phase-screen, whose statistical properties are determined from the statistics of the electron-density irregularities. The waveform then propagates from phase-screen to phase-screen via an exact solution to the Fresnel-Kirchnoff equation. For wide bandwidth waveforms, numerical solutions are obtained at a number of discrete frequencies centered about the carrier and then time-domain solutions are obtained by Fourier transform techniques. Detailed results are presented for a number of interesting cases including propagation of a 20 MHz bandwidth signal through a finite barium cloud at a carrier frequency of 100 MHz. One of the major uses of the MPS propagation simulation has been to provide realizations of the received signal after propagation through a disturbed channel. The MPS simulation obtains a general solution of the parabolic wave equation under both weak and strong scattering conditions. A second technique to directly obtain realizations of wide bandwidth waveforms is presented here. This technique is limited to the case of strong scattering but requires only a fraction of the computer resources needed for MPS signal generation. Detailed comparisons of the two signal generation techniques are presented.

Random Media↗
NASA NTRS1985

Numerical simulation of boundary layer excitation by surface heating/cooling

The concept of active control of growing disturbances in an unstable compressible flow by using time periodic, localized surface heating is studied numerically. The simulations are calculated by a fourth-order accurate solution of the compressible, laminar Navier-Stokes equations. Fourth-order accuracy is particularly important for this problem because the solution must be computed over many wavelengths. The numerical results demonstrate the growth of an initially small fluctuation into the nonlinear regime where a local breakdown into smaller scale disturbances can be observed. It is shown that periodic surface heating over a small strip can reduce the level of the fluctuation provided that the phase of the heating current is properly chosen.

Bayliss, A.↗
NASA NTRS1984

Thermocapillary-driven convection in supported and floating-zone crystallization

Marangoni flow was induced in a thin disk of molten tin with an atomically clean surface by heating it from below in an ultra high vacuum apparatus. The radial distribution of temperature was measured and no temperature oscillations were observed. Strong mechanical disturbances introduced at a Marangoni number of about 4300 died out quickly with time indicating that the system was stable. Mathematical models indicate that strong flows in a two cell structure exist under the conditions studied, and that the velocity profile in the cell near the surface is of the boundary layer type which varies rapidly with depth.

Gill, W. N.↗
NASA NTRS1986

Numerical simulation of boundary-layer excitation by surface heating/cooling

The concept of active control of growing disturbances in an unstable compressible flow by using time periodic, localized surface heating is studied numerically. The simulations are calculated by a fourth-order accurate solution of the compressible, laminar Navier-Stokes equations. Fourth-order accuracy is particularly important for this problem because the solution must be computed over many wavelengths. The numerical results demonstrate the growth of an initially small fluctuation into the nonlinear regime where a local breakdown into smaller scale disturbances can be observed. It is shown that periodic surface heating over a small strip can reduce the level of the fluctuation provided that the phase of the heating current is properly chosen.

Bayliss, A.↗
NASA NTRS1989

Dynamics of the upper middle atmosphere (80-110 km) at Tromsoe, June-December 1987, using the Tromsoe/Saskatoon M.F. radar

A real time winds (RTW) system from Saskatoon operated with the Tromsoe M.F. (partial reflection) radar on a continuous basis, June to December 1987. Profiles with 3 km resolution were obtained every 5 minutes with weak ionization, and few geomagnetic disturbances limited the observations normally to 80 to 110 km. However, daily mean winds, tidal characteristics (24, 12 h) such as amplitudes, phases and wavelengths, and gravity wave characteristics (intensities, mean directions) are available throughout this interval, which includes MAC-SINE and Epsilon. This is particularly valuable in defining the background state for some experiments, e.g., rockets, and for comparison with related parameters from the lidar and other radars (EISCAT, SOUSY-VHF). Comparisons with dynamical parameters from Saskatoon (52 N) are made: the zonal circulation was weaker at Tromsoe, tidal amplitudes smaller, and summer 12 h tidal wavelengths shorter (approx. 80 km vs approx. 100 km). The fall transition for this tide occurred in September, earlier than observed elsewhere. Initial comparisons with other experimental systems are also made.

Manson, A. H.↗
NASA NTRS1991

Bypass transition in boundary layers including curvature and favorable pressure gradient effects

Recent studies of 2-D boundary layers undergoing bypass transition were reviewed. Bypass transition is characterized by the sudden appearance of turbulent spots in boundary layer without first the regular, observable growth of disturbances predicted by linear stability theory. There are no standard criteria or parameters for defining bypass transition, but it is known to be the mode of transition when the flow is disturbed by perturbations of sufficient amplitude.

Volino, R. J.↗
NASA NTRS1991

Magnetization of the ionospheres of Venus and Mars - Results from radio occultation measurements

Remote sensing radio occultation measurements are used here to study magnetization of the ionospheres of Venus and Mars. For Venus, the measurements yield results on frequency of occurrence of magnetization during solar maximum that are similar to those obtained from Pioneer Venus in situ magnetic field measurements. During solar minimum, magnetization of the Venus ionosphere is more pervasive than at solar maximum. Magnetization extends to higher solar zenith angles and appears stronger than at solar maximum. These results confirm that during solar minimum the high solar wind dynamic pressure state is more prevalent at Venus because the ionospheric plasma pressure is weaker than at solar maximum. Comparison of a large number of electron density profiles of Mars with those of Venus shows an absence of the ledge and disturbed topside plasma observed in the Venus profiles. These results do not constitute evidence against magnetization of the ionosphere of Mars.

Woo, Richard↗
NASA NTRS1992

The theory of magnetohydrodynamic wave generation by localized sources. III - Efficiency of plasma heating by dissipation of far-field waves

The fraction of radiation emitted by Alfven waves is calculated by using two separate methods to determine whether the Alfven flux generated in the photosphere is sufficient to heat the corona. One method employs a set of scaling laws for the fluxes as functions of plasma and source parameters; the second method consist of a procedure for calculating the flux in each waveband from the interaction of vector-harmonic components of an arbitrary applied forcing. Both methods indicate that the Alfven flux accounts roughly for half of the total emission. The need to reexamine estimates of the amount of Alfven flux reaching the corona based on observations of plasma disturbances in the photosphere is emphasized.

Collins, William↗
NASA NTRS1947

Exploratory Investigation of Laminar-boundary-layer Oscillations on a Rotating Disk

Sinusoidal waves excited by random disturbances have been observed in the laminar boundary layer of a rotating disk at Reynolds numbers in a narrow range below the Reynolds number of transition. Their frequency was found to be approximately a constant times the velocity of the disk. The velocity of the waves at the radius of 11 inches was determined and found to be 0.2 linear velocity of the disk in a downstream direction, making an angle of approximately 14 degrees with the outward drawn radius vector.

Smith, Newell H↗
NASA NTRS1995

A study of flux transfer events at different planets

Flux transfer events (FTEs) are disturbances in and near the magnetopause current layer that cause a characteristic signature in the component of the magnetic field parallel to the average boundary normal. These disturbances have been observed at Mercury, Earth and Jupiter but not at Saturn, Uranus or Neptune. At Earth, FTEs last about 1 minute and repeat about every 8 but at Mercury, a much smaller magnetosphere, the events last seconds and are tens of seconds apart. These features have been interpreted in terms of magnetospheric flux ropes connected to the interplanetary magnetic field, arising as the result of reconnection. An analogous phenomenon occurs at Venus where magnetic flux ropes arise at the ionosphere, a boundary between a very strongly magnetized one. However, here the flux ropes do not appear to be due to reconnection.

Russell, C. T.↗
NASA NTRS2002

Libration Orbit Mission Design: Applications of Numerical & Dynamical Methods

Sun-Earth libration point orbits serve as excellent locations for scientific investigations. These orbits are often selected to minimize environmental disturbances and maximize observing efficiency. Trajectory design in support of libration orbits is ever more challenging as more complex missions are envisioned in the next decade. Trajectory design software must be further enabled to incorporate better understanding of the libration orbit solution space and thus improve the efficiency and expand the capabilities of current approaches. The Goddard Space Flight Center (GSFC) is currently supporting multiple libration missions. This end-to-end support consists of mission operations, trajectory design, and control. It also includes algorithm and software development. The recently launched Microwave Anisotropy Probe (MAP) and upcoming James Webb Space Telescope (JWST) and Constellation-X missions are examples of the use of improved numerical methods for attaining constrained orbital parameters and controlling their dynamical evolution at the collinear libration points. This paper presents a history of libration point missions, a brief description of the numerical and dynamical design techniques including software used, and a sample of future GSFC mission designs.

Bauer, Frank↗
NASA NTRS2003

Formation Flying Design and Applications in Weak Stability Boundary Regions

Weak Stability regions serve as superior locations for interferometric scientific investigations. These regions are often selected to minimize environmental disturbances and maximize observing efficiency. Design of formations in these regions are becoming ever more challenging as more complex missions are envisioned. The development of algorithms to enable the capability for formation design must be further enabled to incorporate better understanding of WSB solution space. This development will improve the efficiency and expand the capabilities of current approaches. The Goddard Space Flight Center (GSFC) is currently supporting multiple formation missions in WSB regions. This end-to-end support consists of mission operations, trajectory design, and control. It also includes both algorithm and software development. The Constellation-X, Maxim, and Stellar Imager missions are examples of the use of improved numerical methods for attaining constrained formation geometries and controlling their dynamical evolution. This paper presents a survey of formation missions in the WSB regions and a brief description of the formation design using numerical and dynamical techniques.

Folta, David↗
NASA NTRS2012

The Evolution and Fate of Saturn's Stratospheric Vortex: Infrared Spectroscopy from Cassini

The planet-encircling springtime storm in Saturn's troposphere (December 2010-July 2011) produced dramatic perturbations to stratospheric temperatures, winds and composition at mbar pressures that persisted long after the tropospheric disturbance had abated. Observations from the Cassini Composite Infrared Spectrometer (CIRS), supported by ground-based imaging from the VISIR instrument on the Very Large Telescope,is used to track the evolution of a large, hot stratospheric anticyclone between January 2011 and the present day. The evolutionary sequence can be divided into three phases: (I) the formation and intensification of two distinct warm airmasses near 0.5 mbar between 25 and 35N (one residing directly above the convective storm head) between January-April 2011, moving westward with different zonal velocities; (II) the merging of the warm airmasses to form the large single 'stratospheric beacon' near 40N between April and June 2011, dissociated from the storm head and at a higher pressure (2 mbar) than the original beacons; and (III) the mature phase characterized by slow cooling and longitudinal shrinkage of the anticyclone since July 2011, moving west with a near-constant velocity of 2.70+/-0.04 deg/day (-24.5+/-0.4 m/s at 40N). Peak temperatures of 220 K at 2 mbar were measured on May 5th 2011 immediately after the merger, some 80 K warmer than the quiescent surroundings. Thermal winds hear calculations in August 2011 suggest clockwise peripheral velocities of 200400 mls at 2 mbar, defining a peripheral collar with a width of 65 degrees longitude (50,000 km in diameter) and 25 degrees latitude. Stratospheric acetylene (C2H2) was uniformly enhanced by a factor of three within the vortex, whereas ethane (C2H6) remained unaffected. We will discuss the thermal and chemical characteristics of Saturn's beacon in its mature phase, and implications for stratospheric vortices on other giant planets.

Fletcher, Leigh N.↗