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At least 1,279 records · Page 71

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NASA NTRS1981

High latitude stratospheric electrical measurements in fair and foul weather under various solar conditions

Stratospheric electric field and conductivity measurements are presented for sites of latitude greater than 50 deg N GG, during the months of either April or August, in a variety of weather and solar conditions. Vertical electric field data from balloon flights with an average duration of 18 hours at ceiling, in fair weather, are shown to be appropriately modeled by a simple, exponential, altitude-dependent equation. Data collected over electrified clouds and thunderstorms are presented, along with a discussion of the thunderstorm-related electric currents. Current surges in the atmosphere due to DC currents as well as the spheric are calculated, and it is found that in over 1000 hours of balloon data, no direct solar influence is identified except during major flares.

Holzworth, R. H.↗

NASA NTRS1981

The structure and dynamics of the heliospheric current sheet

It has been suggested that the sector structure observed in the interplanetary magnetic field may be interpreted in terms of a warped equatorial current sheet in the heliosphere. The reported study seeks to investigate this suggestion and to provide a clear picture of the topology of the current sheet. An analysis is presented of the magnetic field data obtained by the Pioneer 10 and 11 spacecraft during the time from 1972 to 1976, taking into account a range of heliocentric distances from 1 to 8.5 AU. The single most convincing observation in support of the warped current sheet hypothesis is the almost complete disappearance of the sector structure in the Pioneer 11 data when the spacecraft reaches a heliographic latitude of 16 deg in 1976. The observation suggests that the spacecraft was consistently above the current sheet for a period of several months.

Thomas, B. T.↗

NASA NTRS1982

The induced magnetosphere of Titan

No evidence was found for an intrinsic magnetic field, nor for the development of a bow shock wave, as the corotating Saturnian magnetoplasma convected past Titan during the Voyager 1 close encounter of November 12, 1980. The observation of a well-developed, induced bipolar magnetic tail is evidence, however, of a strong electrodynamic interaction. Three thin, current-carrying regions were crossed which correspond to the inbound and outbound tail magnetopause and an imbedded tail neutral sheet. The interaction is unique among those observed to date in the solar system, in that it is intermediate with respect to sonic and Alfvenic Mach numbers by comparison with Titan in the solar wind and Io in the Jovian magnetosphere. The draping of the Saturnian magnetic field around the ionosphere of Titan is suggested by results of the analysis of magnetic field data.

Ness, N. F.↗

NASA NTRS1981

Ground level reflectance measurement techniques - An evaluation with emphasis on the importance of spectral calibration

The bandpasses, overflight conditions, and sensor geometry that will provide optimum target discrimination in remote-sensing studies can be determined only from spectral reflectance measurements made for various sun-target-sensor geometries, supplemented by model calculations which can be checked against field data. The accurate measurement of ground reflectance properties is critical to the design of future sensors and to the determination of imaging conditions. The current investigation has the objective to review typical methods of measuring spectral reflectance, to point out some of the problems inherent to reflectance measuring techniques, and to present a method of checking measurement accuracy.

Duggin, M. J.↗

NASA NTRS1981

A comprehensive analysis of the performance characteristics of the Mount Laguna solar photovoltaic installation

This paper represents the first comprehensive survey of the Mount Laguna Photovoltaic Installation. The novel techniques used for performing the field tests have been effective in locating and characterizing defective modules. A comparative analysis on the two types of modules used in the array indicates that they have significantly different failure rates, different distributions in degradational space and very different failure modes. A life cycle model is presented to explain a multimodal distribution observed for one module type. A statistical model is constructed and it is shown to be in good agreement with the field data.

Shumka, A.↗

NASA NTRS1982

Instabilities of geared couplings: Theory and practice

The use of couplings for high speed turbocompressors or pumps is essential to transmit power from the driver. Typical couplings are either of the lubricated gear or dry diaphragm type design. Gear couplings have been the standard design for many years and recent advances in power and speed requirements have pushed the standard design criteria to the limit. Recent test stand and field data on continuous lube gear type couplings have forced a closer examination of design tolerances and concepts to avoid operational instabilities. Two types of mechanical instabilities are reviewed in this paper: (1) entrapped fluid, and (2) gear mesh instability resulting in spacer throw-out onset. Test stand results of these types of instabilities and other directly related problems are presented together with criteria for proper coupling design to avoid these conditions. An additional test case discussed shows the importance of proper material selection and processing and what can happen to an otherwise good design.

Kirk, R. G.↗

NASA NTRS1981

The University of Kansas Applied Sensing Program: An operational perspective

The Kansas applied remote sensing (KARS) program conducts demonstration projects and applied research on remote sensing techniques which enable local, regional, state and federal agency personnel to better utilize available satellite and airborne remote sensing systems. As liason with Kansas agencies for the Earth Resources Laboratory (ERL), Kansas demonstration project, KARS coordinated interagency communication, field data collection, hands-on training, and follow-on technical assistance and worked with Kansas agency personnel in evaluating land cover maps provided by ERL. Short courses are being conducted to provide training in state-of-the-art remote sensing technology for university faculty, state personnel, and persons from private industry and federal government. Topics are listed which were considered in intensive five-day courses covering the acquisition, interpretation, and application of information derived through remote sensing with specific training and hands-on experience in image interpretation and the analysis of LANDSAT data are listed.

Martinko, E. A.↗

NASA NTRS1982

Atmospheric turbulence parameters for modeling wind turbine dynamics

A model which can be used to predict the response of wind turbines to atmospheric turbulence is given. The model was developed using linearized aerodynamics for a three-bladed rotor and accounts for three turbulent velocity components as well as velocity gradients across the rotor disk. Typical response power spectral densities are shown. The system response depends critically on three wind and turbulence parameters, and models are presented to predict desired response statistics. An equation error method, which can be used to estimate the required parameters from field data, is also presented.

Holley, W. E.↗

NASA NTRS1983

The relationship between Saturn kilometric radiation and the solar wind

Voyager spacecraft radio, interplanetary plasma, and interplanetary magnetic field data are used to show that large amplitude fluctuations in the power generated by the Saturn kilometric radio emission are best correlated with solar wind ram pressure variation. In all, thirteen solar wind quantities previously found important in driving terrestrial magnetospheric substorms and other auroral processes were examined for evidence of correlations with the Saturn radio emission. The results are consistent with hydromagnetic wave or eddy diffusion processes driven by large scale solar wind pressure changes at Saturn's dayside magnetopause.

Desch, M. D.↗

NASA NTRS1983

Structure and dynamics of Saturn's outer magnetosphere and boundary regions

In 1979-1981, the three USA spacecraft Pioneer 11 and Voyagers 1 and 2 discovered and explored the magnetosphere of Saturn to the limited extent possible on flyby trajectories. Considerable variation in the locations of the bow shock (BS) and magnetopause (MP) surfaces were observed in association with variable solar wind conditions and, during the Voyager 2 encounter, possible immersion in Jupiter's distant magnetic tail. The limited number of BS and MP crossings were concentrated near the subsolar region and the dawn terminator, and that fact, together with the temporal variability, makes it difficult to assess the three dimensional shape of the sunward magnetospheric boundary. The combined BS and MP crossing positions from the three spacecraft yield an average BS-to-MP stagnation point distance ratio of 1.29 +/- 0.10. This is near the 1.33 value for the Earth's magnetosphere, implying a similar sunward shape at Saturn. Study of the structure and dynamical behavior of the outer magnetosphere, both in the sunward hemisphere and the magnetotail region using combined plasma and magnetic field data, suggest that Saturn's magnetosphere is more similar to that of Earth than that of Jupiter.

Behannon, K. W.↗

NASA NTRS1983

The desorptivity model of bulk soil-water evaporation

Available models of bulk evaporation from a bare-surfaced soil are difficult to apply to field conditions where evaporation is complicated by two main factors: rate-limiting climatic conditions and redistribution of soil moisture following infiltration. Both factors are included in the "desorptivity model', wherein the evaporation rate during the second stage (the soil-limiting stage) of evaporation is related to the desorptivity parameter, A. Analytical approximations for A are presented. The approximations are independent of the surface soil moisture. However, calculations using the approximations indicate that both soil texture and soil moisture content at depth significantly affect A. Because the moisture content at depth decreases in time during redistribution, it follows that the A parameter also changes with time. Consequently, a method to calculate a representative value of A was developed. When applied to field data, the desorptivity model estimated cumulative evaporation well. The model is easy to calculate, but its usefulness is limited because it requires an independent estimate of the time of transition between the first and second stages of evaporation. The model shows that bulk evaporation after the transition to the second stage is largely independent of climatic conditions.

Clapp, R. B.↗

NASA NTRS1983

Transfer of pulsation-relation wave activity across the magnetopause: Observations of corresponding spectra by ISEE-1 and ISEE-2

Comparison of power spectra of magnetic field data from ISEE-1 and -2 recorded simultaneously on both sides of the magnetopause showed that power level inside the magnetosphere varied with power level outside in the magnetosheath and suggested that the same frequencies were enhanced on the two sides of the boundary. Power levels were two to three orders of magnitude lower inside than outside the magnetosphere, indicating that wave energy was transmitted inside from the sheath.

Greenstadt, E. W.↗

NASA NTRS1983

Energy and momentum flow in electromagnetic fields and plasma

The energy momentum tensor for a perfect fluid in a magnetic field is used to predict the momentum density, energy density, momentum flow, and energy flow of the fluid and the electromagnetic field. It is shown that taking the momentum flow from the energy momentum tensor, rather than starting with differential magnetohydrodynamic equations, can produce more accurate results on the basis of magnetic field data. It is suggested that the use of the energy momentum tensor has the potential for application to analysis of data from the more dynamic regions of the solar system, such as the plasma boundaries of Venus, the Jovian ionosphere, and the terrestrial magnetopause.

Parish, J. L.↗

NASA NTRS1983

Plasma rest frame frequencies and polarizations of the low-frequency upstream waves - ISEE 1 and 2 observations

The plasma rest frame frequencies and polarizations of the large amplitude low frequency (0.03 Hz) upstream waves are investigated using magnetic field data from the dual ISEE 1 and 2 spacecraft. The monochromatic sinusoidal waves associated with intermediate ion fluxes are propagating in both the Alfven and magnetosonic modes, in both cases with typical frequencies approximately 0.1 times the local proton gyrofrequency and wavelengths of approximately 1 R(E). It is shown that the generation of the magnetosonic mode can be explained by the cyclotron resonance mechanism driven by narrow reflected ion beams, but the concurrent observation of Alfven mode waves appears to require wave generation by the more isotropic diffuse ion distributions as well.

Hoppe, M. M.↗

NASA NTRS1983

Numerical solutions for spin-up from rest in a cylinder

A set of three-dimensional flow-field data for the region around a cylinder impulsively spun-up from rest was derived with a numerical model based on the Navier-Stokes equations. Laser-Doppler anemometer data in the azimuthal direction was employed to test the model predictions, and data was developed for a flowfield with Ekman numbers from 9.18/1,000,000 to 9.18/10,000. The contributions of inviscid and viscous terms were determined as functions of radius and time. It was found that immediately after start-up viscous diffusion is the dominant factor, which is replaced by nonlinear radial advection. The Coriolis force dominates in the later stages of spin-up. The inward radial flow is a maximum near the front, where the vertical velocity is small, but features strong radial gradients, as it does at the edge of the Ekman layer.

Hyun, J. M.↗

NASA NTRS1983

Observations of interplanetary shocks - Recent progress

Attention is given to interplanetary shock observations conducted since 1978, with emphasis on shocks associated with such solar transient phenomena as coronal transients and eruptive prominences, as well as with flares. A correlation between shocks and Storm Sudden Commencements is found to persist into the recent maximum, and shocks associated with disappearing filaments and coronal transients rather than with flares have been identified. Preliminary results on the thickness of interplanetary shocks have been obtained, and several quasi-parallel shocks have been identified which propagate along, rather than across, the magnetic field. The plasma drivers that accompany interplanetary shocks exhibit distinctive features in electric, ion and magnetic field data.

Smith, E. J.↗

NASA NTRS1983

Transfer of pulsation-related wave activity across the magnetopause - Observations of corresponding spectra by ISEE-1 and ISEE-2

Greenstadt, E. W.↗

NASA NTRS1983

ISEE-3 - A late entry in the great comet chase

The ISEE-3 spacecraft, currently in a figure-8 traverse of the geomagnetic tail between 80-220 earth radii, is being redirected to a flyby of the Giacobini-Zinner comet in 1985. The satellite carries experiments for the solar wind plasma, magnetic field data, plasma wave and composition, radio waves, and energetic protons, and can gather data on the solar wind-comet interaction. A double lunar swingby will be employed to establish the intercept trajectory, yielding a total velocity change of 100 m/sec, with a reserve of 100 m/sec for midcourse corrections. The comet will be encountered at a distance of 3000 km in September 1985, followed by passage through the Halley's comet tail 5000 km from the nucleus in March 1986.

Farquhar, R.↗