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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Solar wind heat flow

The ability of a theoretical solar wind model to predict the energy flux density due to heat conduction was investigated. In order to demonstrate this capability, the analysis used simultaneous data from the electron plasma experiment of Ogilvie and Lind, and the vector magnetic field data of Heppner and Sugiura on OGO-5. On the strength of two independent, different, and consistent experimental determinations of the conduction of heat flux by electrons at 149.6 gigameters(1 AU), it was determined that the models for the solar wind must be able to predict a value for the heat conduction in the range 0.007 to 0.008 in order to be in agreement with the observations.

Scudder, J.↗
NASA NTRS1988

Applications of the Coastal Zone Color Scanner in oceanography

Research activity has continued to be focused on the applications of the Coastal Zone Color Scanner (CZCS) imagery in oceanography. A number of regional studies were completed including investigations of temporal and spatial variability of phytoplankton populations in the South Atlantic Bight, Northwest Spain, Weddell Sea, Bering Sea, Caribbean Sea and in tropical Atlantic Ocean. In addition to the regional studies, much work was dedicated to developing ancillary global scale meteorological and hydrographic data sets to complement the global CZCS processing products. To accomplish this, SEAPAK's image analysis capability was complemented with an interface to GEMPAK (Severe Storm Branch's meteorological analysis software package) for the analysis and graphical display of gridded data fields. Plans are being made to develop a similar interface to SEAPAK for hydrographic data using EPIC (a hydrographic data analysis package developed by NOAA/PMEL).

Mcclain, C. R.↗
NASA NTRS1989

Plasma pressure in the environment of Jupiter, inferred from Voyager 1 magnetometer observations

A model combining the internal magnetic field with a self-consistent model of the Jovian magnetodisc was fitted to the Voyager 1 Jovian magnetic field data by means of a generalized inverse technique. The model parameters included the internal field spherical harmonic coefficients as well as with parameters describing the plasma distribution in the magnetosphere. Assuming that the pressure in the middle and outer magnetosphere is related to the unit flux tube volume V through PV exp gamma = const, the model fit yielded a value of 0.88 for gamma. If the hot (30 keV) plasma is transported adiabatically inward under the interchange instability triggered by centrifugal force of the heavy torus ions, losses are not sufficient to account for such a low value of gamma beyond L = 10. Closer to the planet, as the outer edge of the Io plasma torus is approached, PV exp gamma is found to decrease inward, as expected from the particle measurements, which identified an inner boundary of the particle fluxes in that region. With the present stage of the development of magnetodisc models, secular variations of the internal field still remain difficult to estimate.

Caudal, G.↗
NASA NTRS1993

Radial and latitudinal variations of the magnetic field strength in the outer heliosphere

The radial, latitudinal, and temporal variations of the magnetic field in the outer heliosphere are analyzed on the basis of observations from Voyagers 1 and 2 and Pioneers 10 and 11. The radial variation of the magnetic field strength measured during 1973-1989 from 1 to 19 AU is compared with that predicted by Parker's (1963) spiral field model. Additional Voyager 2 magnetic field data from 1986 through most of 1989 are discussed. Latitudinal variations in the magnetic field strength are examined on Voyager 1 and 2 observations from 1981 to 1989. It is concluded that both the Voyager and the Pioneer observations are consistent with Parker's model for the variation of the strength of the magnetic field as a function of distance from the sun in the region from 1 to 19 AU. The topology of the spiral interplanetary magnetic field, as well as a program for analyzing more general magnetic fields and velocity fields in the heliosphere are also discussed.

Burlaga, L. F.↗
NASA NTRS1994

Geotail observations of spiky electric fields and low-frequency waves in the plasma sheet and plasma sheet boundary

Electric field data from the Geotail spacecraft provide an opportunity to extend the observations of spiky fields made by International Sun Earth Explorer-1 (ISEE-1) to a region of the magnetosphere where quasistatic electric field measurements have not previously been msde, to examine their possible importance in the dynamics of the middle and distant tail, and to test some hypotheses about their formation. In this paper, examples of large fields in the plasma sheet and its boundary at radial distances up to approximately 90 R(sub E) are presented. It is shown that three different types of large electric fields can occur: (1) spiky fields; (2) 'DC' fields; and (3) waves at frequencies comparable to the lower hybrid frequency. There is usually a gradation between (1) and (3), and often large electric field spikes are embedded in regions of lower amplitude waves. The waves tend to occur in short (few to 10's of seconds) packets whose start and stop times are not always correlated with changes in the magnetic field and/or density (as indicated by the spacecraft potential). The peak frequency is often less than but comparable to the lower hybrid frequency in agreement with theories of lower hybrid drift waves in the magnetotail. The largest spikes are not always associated with the largest changes in the spacecraft potential and/or magnetic field. It is suggested that the spiky fields may represent the nonlinear development of the waves.

Cattell, C.↗
NASA NTRS2002

Magnetic Properties of Lunar Geologic Terranes: New Statistical Results

We use global magnetic field data and digitized geologic maps to determine the magnetic properties of lunar terranes. Average fields vary by a factor of 100 from demagnetized impact basins and craters to strongly magnetized antipodal regions. Additional information is contained in the original extended abstract.

Halekas, J. S.↗
NASA NTRS2003

A Bayesian Approach to Sensor Characterization

The physical model of a generic electro-optic sensor is derived and incorporated into a Bayesian framework for the estimation of key instrument parameters from calibration data. The sensor characterization thus achieved enables optimal subsequent removal of instrument effects from field data, leading to the highest possible accuracy in the retrieved physical quantities.

Timucin, Dogan A.↗
NASA NTRS2009

RANS Analyses of Turbofan Nozzles with Internal Wedge Deflectors for Noise Reduction

Computational fluid dynamics (CFD) was used to evaluate the flow field and thrust performance of a promising concept for reducing the noise at take-off of dual-stream turbofan nozzles. The concept, offset stream technology, reduces the jet noise observed on the ground by diverting (offsetting) a portion of the fan flow below the core flow, thickening and lengthening this layer between the high-velocity core flow and the ground observers. In this study a wedge placed in the internal fan stream is used as the diverter. Wind, a Reynolds averaged Navier-Stokes (RANS) code, was used to analyze the flow field of the exhaust plume and to calculate nozzle performance. Results showed that the wedge diverts all of the fan flow to the lower side of the nozzle, and the turbulent kinetic energy on the observer side of the nozzle is reduced. This reduction in turbulent kinetic energy should correspond to a reduction in noise. However, because all of the fan flow is diverted, the upper portion of the core flow is exposed to the freestream, and the turbulent kinetic energy on the upper side of the nozzle is increased, creating an unintended noise source. The blockage due to the wedge reduces the fan mass flow proportional to its blockage, and the overall thrust is consequently reduced. The CFD predictions are in very good agreement with experimental flow field data, demonstrating that RANS CFD can accurately predict the velocity and turbulent kinetic energy fields. While this initial design of a large scale wedge nozzle did not meet noise reduction or thrust goals, this study identified areas for improvement and demonstrated that RANS CFD can be used to improve the concept.

DeBonis, James R.↗
NASA NTRS1989

A search for the solar roots of the most disturbed interplanetary field intervals of solar cycle 21

During the course of the Pioneer Venus Orbiter mission, fairly continuous interplanetary plasma and magnetic field data were obtained which span the interval from prior to the last solar maximum to the current solar minimum recovery. Within this nearly complete solar cycle interval, several periods of exceptional disturbance of the interplanetary field stand out. The available solar data have been examined to determine what features, if any, distinguish these periods. Neither flare nor coronal mass ejection reports show particularly unusual behavior. However, these periods appear to occur in conjunction with marked changes in the interplanetary sector structure. This suggests that heliospheric current sheet reconfiguration is an indicator of the level of interplanetary disturbance distinct from the more traditional solar activity data.

Luhmann, J. G.↗
NASA NTRS1989

Processing of DMSP magnetic data and its use in geomagnetic field modeling

The DMSP F-7 satellite is an operational Air Force meteorological satellite which carried a magnetometer for geophysical measurements. The magnetometer was located within the body of the spacecraft in the presence of large spacecraft fields. In addition to stray magnetic fields, the data have inherent position and time inaccuracies. Algorithms were developed to identify and remove time varying magnetic field noise from the data. Techniques developed for Magsat were then modified and used to attempt determination of the spacecraft fields, of any rotation between the magnetometer axes and the spacecraft axes, and of any scale changes within the magnetometer itself. The corrected data were then used to attempt to model the geomagnetic field. This was done in combination with data from Magsat, from the standard magnetic observatories, from aeromagnetic and other survey data, and from DE-2 spacecraft field data. Future DMSP missions can be upgraded in terms of geomagnetic measurements by upgrading the time and position information furnished with the data, placing the magnetometer at the end of the boom, upgrading the attitude determination at the magnetometer, and increasing the accuracy of the magnetometer.

Ridgway, J. R.↗
NASA NTRS1991

The Aerospace Database data element dictionary with issues and recommendations from the meetings of July 24-25, August 13-14, and September 24-25, 1991

The present volume contains descriptions of the individual fields (data elements) which comprise the bibliographic records of the Aerospace Database. Indexes by field name and field mnemonic are provided. In addition, the issues and recommendations defined by the NASA STI Database Upgrade Working Group are included as annotations to the individual field descriptions and are listed at the end of the volume. The activities of the Working Group were initiated by the NASA STI Program Coordinating Council as part of an effort to improve overall database quality.

Source record↗
NASA NTRS1972

Space science experiments aboard ATS-F.

The Environmental Measurements Experiment (EME) package is mounted on the ATS-F spacecraft to a structure that is located on top of the 30-foot parabolic reflector hub. The eight experiments of the EME package are designed to study the environment in space at synchronous altitude and to obtain information on electromagnetic-ionospheric interactions. Six of these experiments will obtain data on charged particles of several different types. A seventh experiment is to provide magnetic field data. The eighth experiment is concerned with solar cell degradation studies.

Wales, R.↗
NASA NTRS1975

Waves in the vicinity of the magnetopause

Magnetic field data from the IMP 6 spacecraft are used in an attempt to clarify the magnetic field microstructure of the magnetopause. After discussing the problems in identifying the magnetopause, and the difficulties in determining normal components, the presence of waves in the vicinity of the magnetopause is discussed. The downstream magnetopause is considered and the presence of surface waves on the tail boundary is demonstrated.

Fairfield, D. H.↗
NASA NTRS1985

Alignment of velocity and field changes across tangential discontinuities in the solar wind

Three-dimensional IMP 8 and Voyager 2 plasma and field data are used to investigate the relative changes in direction of the velocity and magnetic field vectors across tangential discontinuities in the solar wind. It is found that Delta-v and Delta-B/rho exp 1/2 are closely aligned either parallel or antiparallel to each other in the sense associated with the propagation of Alfven waves or rotational discontinuities outward from the sun. This alignment is observed at all solar distances betwen 1 and 2.2 AU and is independent of the solar wind stream structure. Several possible causes of the effect are briefly discussed, including interplanetary turbulence, the propagation of large-amplitude Alfvenic fluctuations traveling independently through the solar wind on both sides of the discontinuities, and the propagation of surface waves on tangential discontinuities.

Neugebauer, M.↗
NASA NTRS1986

Tangential discontinuities in the solar wind - Correlated field and velocity changes and the Kelvin-Helmholtz instability

Three-dimensional Helios plasma and field data are used to investigate the relative changes in direction of the velocity and magnetic field vectors across tangential discontinuities (TDs) in the solar wind at solar distances of 0.29-0.50 AU. It is found for TDs with large Delta-v and (Delta-B)/B that Delta-v and Delta-B are closely aligned with each other, in agreement with the unexpected results of previous studies of TDs observed at 1 AU and beyond. It is shown that this effect probably results from the destruction by the Kelvin-Helmholtz instability of TDs for which Delta-v and Delta-B are not aligned. The observed decrease in the number of interplanetary discontinuities with increasing solar distance may be associated with the growth of the Kelvin-Helmholtz instability with decreasing Alfven speed.

Neugebauer, M.↗
NASA NTRS1987

Retrieval of surface roughness parameters from dual-frequency measurements of radar backscattering coefficients

The use of dual-frequency data of backscattering coefficients at a fixed angle to estimate surface roughness parameters is evaluated. Radar backscattering coefficients at 1.5 and 4.25 GHz are calculated using a model based on Kirchhoff approximation of electromagnetic wave scatttering from a rough soil surface. Plots of the calculated backscattering coefficients for Kansas soil moisture contents at the C- and L-band frequencies and HH polarization are analyzed. The effects of changes in correlation length on the backscattering coefficients are investigated. The calculated backscattering coefficients are compared with scatterometer data collected at 1.5 and 4.25 GHz, and it is detected that the model and field data correlate well. The data reveal that it is possible to retrieve the surface roughness parameters from measured radar data.

Mo, Tsan↗
NASA NTRS1986

Satellite data in aquatic area research - Some ideas for future studies

Attempts to apply aquatic remote sensing to the preparation of parametric map-like presentations, quantitative evaluations and time-related investigations in various water areas in Finland are presented. The potential use of Landsat MSS data in aquatic area studies, including limology, aquatic botany, geomorphology and engineering is evaluated using computer-aided digital remote sensing techniques. MSS data may provide information about depth, Secchi disc values, humus content in water, and productivity. Aquatic vegetation classification using MSS is possible only where vegetation units are large enough in respect to the 0.5 hectares ground resolution. Multitemporal satellite imagery has been used to evaluate alterations in the littoral areas of some Finnish water reservoirs between successive periods of high water. It is concluded that although MSS data can be of use in aquatic studies, it should be used in connection with field data and/or TM and SPOT data.

Raitala, Jouko T.↗
NASA NTRS1987

Distinguishing among electron injection types

Three types of electron injections taking place in the near-earth region of the magnetotail have been distinguished previously using SCATHA particle and field data. Defining characteristics are given here for each type of event, and the positions of the magnetosphere where they are expected to occur are discussed. These three event types can be difficult to distinguish in data sets that are more limited than the SCATHA set that carried instruments detecting magnetic fields and charged particles over an energy range from eVs to MeVs. It is suggested that determining the magnetospheric regions at which each of these event types occurs will considerably clarify the phenomenological description of substorms available for theoretical analysis.

Feynman, J.↗