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Wolf, R. A.

Publications and source records attributed to Wolf, R. A..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Quantitative simulation of a magnetospheric substorm. II - Comparison with observations

Results of the computer simulation of the behavior of the inner magnetosphere during the substorm-type event of September 19, 1976, are discussed. The computed electric fields are found to compare satisfactorily with electric fields measured from S3-2, although there are detailed differences. The three general features on which the model and observations are in good agreement are (1) the magnitude and direction of the high-latitude electric field, (2) the degree to which the low-latitude ionosphere is shielded from the high-latitude convection electric field, and (3) the fact that the poleward electric field on the duskside is significantly larger, on the average, than the equatorward electric field on the dawnside. Simple formulas are presented that give rough estimates of global Joule heating rates from observable parameters.

Harel, M.↗
NASA NTRS1981

Quantitative simulation of a magnetospheric substorm. III - Plasmaspheric electric fields and evolution of the plasmapause

Results of a substorm simulation are used to investigate the penetration of substorm-associated electric fields into the plasmasphere. Near 4 earth radii in the equatorial plane, the time-dependent electric field model is characterized by eastward components in the dusk-midnight local time sector and westward components after midnight. With the exception of a small region just before dusk, the model predicts eastward electric field components throughout the daytime sector. The characteristic radial component is directed inward at all local times with the exception of a small region just after dawn. It is noted that these results compare favorably with available whistler and incoherent-scatter radar measurements obtained during magnetically disturbed periods. By assuming an initial plasmapause shape and by following the computed E x B drift trajectories of plasma flux tubes from that initial boundary, the short-term evolution of the plasmapause during the substorm-like event of September 19, 1976, is examined.

Spiro, R. W.↗
NASA NTRS1980

Installation and checkout of the DOE/NASA Mod-1 2000-kW wind turbine generator

The paper describes the DOE/NASA Mod-1 wind turbine generator, its assembly and testing, and its installation at Boone, North Carolina. The paper concludes with performance data taken during the initial tests conducted on the machine. The successful installation and initial operation of the Mod-1 wind turbine generator has had the following results: (1) megawatt-size wind turbines can be operated satisfactorily on utility grids; (2) the structural loads can be predicted by existing codes; (3) assembly of the machine on top of the tower presents no major problem; (4) large blades 100 ft long can be transported long distances and over mountain roads; and (5) operating experience and performance data will contribute substantially to the design of future low-cost wind turbines.

Puthoff, R. L.↗
NASA NTRS1979

Computer modeling of events in the inner magnetosphere

The first effort at computer simulating the behavior of the inner magnetosphere during a substorm-type event on 19 September 1976 was completed. The computer model simulates many aspects of the behavior of the closed-field-line portion of the earth's magnetosphere, and the auroral and subauroral ionosphere. For these regions, the program self-consistently computes electric fields, electric currents, hot-plasma densities, plasma flow velocities and other parameters. Highlights of the results of our event simulation are presented. Predicted electric fields for several times during the event agree reasonably well with corresponding data from satellite S3-2. Detailed discussion is presented for a case of rapid subauroral flow that was observed on one S3-2 pass and is predicted by the computer runs. The computed global distribution of Birkeland current agrees reasonably well with the observations of Iijima and Potemra.

Harel, M.↗
NASA NTRS1978

An operating 200-kW horizontal axis wind turbine

The Mod-OA wind turbine blades were rotated for the first time on November 30, 1977, establishing the Mod-OA as the first wind-driven generator in 35 years to be continually tied into an electrical power system which services a community. Tower-mounted equipment and blade structural design and fabrication are discussed.

Hunnicutt, C. L.↗
NASA NTRS1978

An operating 200 kW horizontal axis wind turbine

Output from the 200-kilowatt machine will be enough to meet the power requirements of about 60 families. The experimental wind turbine generator (WTG) is a two-bladed, horizontal-axis, rotor system driving a synchronous electric generator through a step-up gear box located within a nacelle. The nacelle is mounted on top of a 100-foot tower with the rotor located downwind from the tower. The 200-kilowatt rated power output of the wind turbine is achieved at a turbine rotor speed of 40 rpm and a rated wind speed of 18.3 mph. The rated wind speed is defined as the lowest wind speed at which full power is achieved. Attention is given to operational details, aspects of blade design, blade fabrication, the use of strain gages, questions of aeroelastic stability, and an early analysis of test data.

Hunnicutt, C. L.↗
NASA NTRS1976

Mercury and Mars - The role of ionospheric conductivity in the acceleration of magnetospheric particles

Although Mercury and Mars appear to have magnetospheres of comparable size, Mercury's magnetosphere accelerates charged particles, whereas Mars' magnetosphere apparently does not. We propose that this difference results from the fact that rapid steady-state convection, and the associated particle acceleration, cannot occur in a Martian magnetosphere because of its connection to a highly conducting ionosphere. Mercury, which has no conducting ionosphere and probably an insufficiently conducting surface, can exhibit rapid solar-wind-induced convection and hence particle acceleration in its magnetospheric tail.

Hill, T. W.↗
NASA NTRS1976

Depletion of solar wind plasma near a planetary boundary

A mathematical model is presented that describes the squeezing of solar wind plasma out along interplanetary magnetic field lines in the region between the bow shock and the effective planetary boundary (in the case of the earth, the magnetopause). In the absence of local magnetic merging the squeezing process should create a 'depletion layer', a region of very low plasma density just outside the magnetopause. Numerical solutions are obtained for the dimensionless magnetohydrodynamic equations describing this depletion process for the case where the solar wind magnetic field is perpendicular to the solar wind flow direction. For the case of the earth, the theory predicts that the density should be reduced by a factor exceeding 2 in a layer about 700-1300 km thick if the Alfven Mach number in the solar wind, is equal to 8. Scaling of the model calculations to Venus and Mars suggests layer thicknesses about 1/10 and 1/15 those of the earth, respectively, neglecting diffusion and ionospheric effects.

Zwan, B. J.↗
NASA NTRS1976

Convection

We review the status of theoretical work on magnetospheric convection in the lower auroral zone and at midlatitudes, and compare with various observed features, such as ionospheric electric fields and plasma flows, the form of the plasmasphere, and the distribution of plasma-sheet particles. We present preliminary results from a new series of computerized convection models, which follow the time evolution of the inner magnetosphere (L less than around 10), self-consistently including ionospheric currents and Birkeland currents, as well as the currents generated in a model plasma sheet with a realistic energy spectrum. We find that the model plasma sheet's inner edge quickly becomes rather sharp. Computed electric field distributions resemble those obtained earlier for a simple single-energy plasma sheet.

Harel, M.↗
NASA NTRS1974

The motion and magnetic structure of the plasma sheet near 30 earth radii

Data taken by the NASA-GSFC magnetometer aboard the Explorer 34 satellite are analyzed in an effort to ascertain the average motion and magnetic field structure of the plasma sheet near 30 earth radii. It is found that the flapping motion of the plasma sheet in the solar ecliptic Z-coordinate is characterized by a typical speed of 90 km/sec and an amplitude of plus or minus 2 earth radii. Results suggest that there exists a layer of nearly uniform cross-tail current density in the central region of the plasma sheet approximately 2.3-2.6 earth radii thick within which the solar-magnetospheric X-component of the magnetic field changes from 10 gamma to -10 gamma.

Bowling, S. B.↗
NASA NTRS1974

Convection in a Martian magnetosphere

Data from the Mars 2 and 3 orbiters suggest the existence of a Martian magnetosphere. We wish to point out that the Martian magnetosphere would probably be one in which the drag on magnetic field lines tied to a highly conducting day side ionosphere greatly inhibits the line-merging rate at the magnetopause. We deduce a maximum merging speed that is 1-2 orders of magnitude less than the local Alfven speed. We also conclude that the magnetospheric magnetic fields caused by ionospheric currents should be comparable to those due to the small intrinsic dipole moment implied by the spacecraft data. The shape and the size of the magnetosphere are likely to be highly variable.

Rassbach, M. E.↗
NASA NTRS1973

Magnetospheric plasma motion during a sudden commencement.

A sudden commencement occurred at 2348 UT on Feb. 15, 1967, when the ATS-1 satellite was about 2 hr past local noon at a geocentric distance of 6.6 earth radii. Plasma was observed by the Suprathermal Ion Detector first to flow in the antisolar direction, as expected, but then to flow westward, for about 2 min, at about 50 km/sec. Analysis of ground magnetograms suggests that the surprising westward flow, which must have involved an electric field of about 10 mV/m at 6.6 earth radii, resulted from the ionosphere's reaction to the sudden commencement. Beginning about 2 min before the start of the westward flow at ATS-1, ground magnetometers near the foot of the ATS-1 field line typically recorded magnetic-field deflections of about 70 gamma, to the northeast. Taking the ground observations, assuming a height-integrated Hall conductivity of 1 mho, and a standoff distance of 7.2 earth radii inferred from Explorer 33 solar-wind data, a magnetospheric electric field is derived which agrees in magnitude and direction with that required to produce the observed flow at ATS-1.

Lin, C.-A.↗
NASA NTRS1972

The estimation of masses of individual galaxies in clusters of galaxies.

Three different methods of estimating masses are discussed. The 'density method' is based on the analysis of the density distribution of galaxies around the object whose mass is to be found. The 'bound-galaxy method' gives estimates of the mass of a double, triple, or quadruple system from analysis of the orbital motion of the components. The 'virial method' utilizes the formulas derived for the second method to obtain estimates of the virial-theorem masses of whole clusters, and thus to obtain upper limits on the mass of an individual galaxy in a cluster. The analytic formulas are developed and compared with computer experiments, and some applications are given.

Wolf, R. A.↗
NASA NTRS1972

On the balance of stresses in the plasma sheet.

The stress resulting from magnetic tension on the neutral sheet must, in a steady state, be balanced by any one or a combination of (1) a pressure gradient in the direction along the axis of the tail, (2) a similar gradient of plasma flow kinetic energy, and (3) the tension resulting from a pressure anisotropy within the plasma sheet. Stress balance in the first two cases requires that the ratios h/LX and BZ/BX be of the same order of magnitude, where h is the half-thickness of the neutral sheet, LX is the length scale for variations along the axis of the tail, and BZ and BX are the magnetic field components in the plasma sheet just outside the neutral sheet. The second case requires, in addition, that the plasma flow speed within the neutral sheet be of the order of or larger than the Alfven speed outside the neutral sheet. Stress balance in the third case requires that just outside the neutral sheet the plasma pressure obey the marginal firehose stability condition.

Rich, F. J.↗
NASA NTRS1968

Transfer processes in the magnetopause.

Magnetic field fluctuations in vicinity of magnetopause boundary layer imply substantial transfer of particles and momentum from solar wind to magnetosphere

Eviatar, A.↗