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At least 145 records · Page 8

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NASA NTRS1974

First order latitude effects in the solar wind

The Weber-Davis model of the solar wind is generalized to include the effects of latitude. The principal assumptions of perfect electrical conductivity, rotational symmetry, a polytropic relation between pressure and density, and a flow aligned magnetic field in a system rotating with the Sun, are retained. The original three dimensional magnetohydrodynamic flow problem is reduced to a two dimensional hydrodynamic flow problem. The solution at 1 Au is most sensitive to a latitudinal dependence in the coronal boundary temperature and least sensitive to a latitudinal dependence in the magnetic field magnitude. A solution obtained for an approximate dipolar variation in the coronal magnetic field magnitude predicts that the latitudinal flow is initially toward the equator due to magnetic channeling; however, this effect is rapidly overcome and the latitudinal flow at 1 Au is toward the pole and not significantly different from the solution for constant boundary conditions.

Winge, C. R., Jr.↗

NASA NTRS1974

Jupiter's radiation belts

Fluxes of electrons and protons in Jupiter's radiation belts are calculated with the source (radial diffusion inward from the solar wind) and the loss (synchroton radiation). The calculations are tested against the measured radio-wave wavelength distribution, the radio-wave distribution with distance from Jupiter, and the degree of polarization of the radio waves. The Fokker-Planck equation is solved by using the method of Farley and Walt (1971) with the fixed flux at the outer boundary and the zero flux at Jupiter's surface. It is found, in agreement with Brice and McDonough (1973), Jacques and Davis (1973), and Birmingham et al. (1974), that the usual magnetic and electric diffusions, which vary as L to the 10th power and L to the 6th power, respectively, are insufficient to furnish the required electrons and that the diffusion driven by ionospheric winds of Brice and McDonough is strong enough to furnish Jupiter's belts. An additional loss mechanism close to Jupiter is required to remove the electrons, particularly those at low energies.

Stansberry, K. G.↗

NASA NTRS1976

Storm-associated variations of equatorially mirroring ring current protons, 1-800 keV, at constant first adiabatic invariant

Explorer 45 observations of ring current protons mirroring near the equator, 1-800 keV, are presented at constant first adiabatic invariant mu throughout the period of the December 17, 1971, geomagnetic storm. The parameter mu is obtained from simultaneous magnetic field and particle observations. Particle deceleration in response to the storm time magnetic field decrease causes ring current measurements viewed at constant energy to underestimate the storm time increase in proton intensities at energies not exceeding 200 keV. This adiabatic deceleration also accounts for the large flux decreases observed at energies above 200 keV during the storm, in contradiction with previous results (Soraas and Davis, 1968) obtained using a model for the storm time magnetic field.

Lyons, L. R.↗

NASA NTRS1976

Limit on the secular change of the gravitational constant based on studies of solar evolution

The past and present observable properties of the sun have been theoretically calculated on the assumption that the gravitational constant G increases or decreases with time. Consideration of Davis's experimental upper limit on the present solar neutrino flux and of terrestrial paleontological data sets a limit on the absolute rate of change of G, namely, the absolute value of the quotient of the change in the gravitational constant and the gravitational constant is less than 1/10 billion/yr, if other standard constants do not also change with time.

Chin, C.-W.↗

NASA NTRS1976

Magnetic acceleration of winds from solar-type stars

The spin-down of solar type stars (F5 V to G3 V) is generally ascribed to the outflow of magnetized plasma in the form of a wind. Magnetically coupled stellar winds are thought to provide the dominant mechanism for angular momentum loss over the entire main-sequence lifetime of stars possessing hydrogen convective zones. The associated loss in rotational kinetic energy can strongly affect the energetics of winds emanating from such stars, for sufficiently high rotation rates and magnetic field strengths. In the present paper, an attempt is made to describe qualitatively how MHD plasma outflow from a rotating star adjusts itself to a broad range of stellar conditions, including fast, intermediate, and slow magnetic rotator configurations. Using the Weber and Davis (1967) model of MHD winds, it is shown that the magnetic deceleration of an MHD wind is of importance when the loss of rotational kinetic energy due to magnetic braking exceeds the energy flux due to thermal processes alone.

Belcher, J. W.↗

NASA NTRS1978

The McDonald Observatory lunar laser ranging project

A summary of the activities of the McDonald lunar laser ranging station at Fort Davis for the FY 77-78 fiscal year is presented. The lunar laser experiment uses the observatory 2.7m reflecting telescope on a thrice-per-day, 21-day-per-lunation schedule. Data are recorded on magnetic tapes and sent to the University of Texas at Austin where the data is processed. After processing, the data is distributed to interested analysis centers and later to the National Space Science Data Center where it is available for routine distribution. Detailed reports are published on the McDonald operations after every fourth lunation or approximately once every 115 days. These reports contain a day-by-day documentation of the ranging activity, detailed discussions of the equipment development efforts, and an abundance of other information as is needed to document and archive this important data type.

Silverberg, E. C.↗

NASA NTRS1979

Lunar laser ranging data identification and management

Activity under the subject grant during the first half of fiscal year 1979 at the University of Texas at Austin is reported. Raw lunar laser ranging data submitted by McDonald Observatory, Fort Davis, Texas and by the Australian Division of National Mapping at Orroral Valley, Australia were processed. This processing includes the filtering of signal events from noise photons, normal point formation, data archive management, and data distribution. System-wide program maintenance and up-grade carried out wherever and whenever necessary. Lunar laser ranging data is being transmitted from Austin to Paris for the extraction of earth rotation information during the EROLD campaign.

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NASA NTRS1978

The sensitivity of the general circulation to Arctic Sea ice boundaries - A numerical experiment

Results are presented for a set of numerical experiments conducted with the Goddard (formerly GISS) general circulation model. The experiments were designed to test the model atmospheric response to a single fixed and specified parameter, the total ice cover in the Davis Strait, Barents Sea, East Greenland Sea, Sea of Okhotsk and Bering Sea. Margin variations are considered that are substantially smaller than those involved in ice age or ice-free Arctic simulations. Anomaly is defined as the mean of two runs corresponding to climatological maximum sea ice conditions. Model results indicate that the ice margin anomalies are capable of altering local climates in certain regions of high and middle latitudes. Possible interactions between high latitudes and subtropical regions are suggested.

Herman, G. F.↗

NASA NTRS1970

Scientific Rationale Summaries for Apollo Candidate Lunar Exploration Landing Sites - Case 340

A summary of the scientific rationale for each Apollo landing site listed by the Group for Lunar Exploration Planning on February 7, 1970 is presented. These sites include the Fra Mauro Formation, Littrow, Censorinus, Davy crater chain, Marius Hills, Descartes, Tycho, Copernicus central peaks, and Hadley-Apennines. In addition, a summary of the scientific rationale for Flamsteed P, the Apollo 13 backup site, and Hyginus is presented.

Head, J. W.↗

NASA NTRS1979

The response of the Goddard general circulation model to sea ice boundary conditions

The effect of variation in the location of Arctic sea ice boundaries on the model's mean monthly climatology was examined. When sea ice boundaries were at their maximum extent the differences resulted in the January-February climatology. Sea level pressure was higher over the Barents Sea, in the Davis Strait, and in the Sea of Okhotsk. Pressure was lower by as much as 8 mb in the North Atlantic between Iceland and the British Isles, and in the Gulf of Alaska. Pressure rises in the eastern subtropical regions of the North Atlantic and North Pacific accompanied pressure falls in the Gulf of Alaska and Icelandic region. Geopotential heights at 500 mb were more than 100 gpm lower in the Bering Sea, and more than 120 gpm lower in the Icelandic region. Zonally averaged temperatures were cooler by 4 deg C below 3800 mb between 50 deg and 70 deg N with little change elsewhere. Zonally averaged geopotentials were lower by as much as 70 gpm in the mid-troposphere between 50/-70 deg N and zonal winds increased by as much as 3 m s in the mid-troposphere between 35/-50 deg N.

Herman, G.↗

NASA NTRS1980

On the VLBI-satellite laser ranging Iron Triangle intercomparison experiment

Simulations were performed to determine the suitability of the proposed station locations. The criterion was a comparison among the possible station configuration of the standard deviations of baseline and Earth rotation parameters estimated from a least squares covariance analysis. Only the relative magnitudes of the standard deviations were addressed in the analysis. Only random errors were assumed and no provision was made for systematic effects. The Iron Triangle, consisting of the stations at Westford (Haystack), Massachusetts, Owens Valley, California, and Ft. Davis, Texas, was regarded as the structure of the proposed network with options to incorporate either the Goldstone, California, or Green Bank, West Virginia, station or both. It was decided to include the Richmond, Florida, station in the analysis since it offered more North-South separation and therefore could strengthen the geometry of the network especially in the recovery of Earth rotation parameters.

Bock, Y.↗

NASA NTRS1980

Energy transfer in NH3-He collisions

The paper presents a new electron gas intermolecular NH3-He potential determined by the Hartree-Fock results of Davis, Boggs, and Mehrotra (1979) with semiempirical long-range induction and dispersion terms. The resulting potential agrees with beam scattering and pressure broadening measurements; it was also found that the quadrupole induced dipole interaction is not as effective as the short range anisotropy. It was concluded that discrepancies remain in the quantitative description of energy transfer in the NH3-He system; discrepancies result from improper consideration of the dependence of cross-sections on degenerate magnetic quantum levels in the experimental investigation.

Green, S.↗

NASA NTRS1981

Anisotropic magnetohydrodynamic turbulence in a strong external magnetic field

A strong external dc magnetic field introduces a basic anisotropy into incompressible magnetohydrodynamic turbulence. The modifications that this is likely to produce in the properties of the turbulence are explored for the high Reynolds number case. The conclusion is reached that the turbulent spectrum splits into two parts: an essentially two dimensional spectrum with both the velocity field and magnetic fluctuations perpendicular to the dc magnetic field, and a generally weaker and more nearly isotropic spectrum of Alfven waves. A minimal characterization of the spectral density tensors is given. Similarities to measurements from the Culham-Harwell Zeta pinch device and the UCLA Macrotor Tokamak are remarked upon, as are certain implications for the Belcher and Davis measurements of magnetohydrodynamic turbulence in the solar wind.

Montgomery, D.↗

NASA NTRS1981

An assessment of theoretical models for viscous and transonic flow

Topics discussed include shear flow models, simplified models for treating separation, classical linear theory, a local linearization theory, a transonic linear theory, a transonic nonlinear theory, the experiment of Davis, and the experiment of Tijdeman. It is concluded that shear flow models, which have proven very accurate in taking into account boundary layer effects for panel flutter, are likely to be less so for lifting surface flutter. For many applications in transonic flow, transonic linear theory will be adequate.

Dowell, E. H.↗

NASA NTRS1980

Indentifying environmental features for land management decisions

The wetlands and water-related land use in the Uinta Basin were classified and mapped using photointerpretation of U-2 infrared photography and digital LANDSAT data. The digital maps were used to augment photointerpretations. A highly effective diagnostic tool emerged when the LANDSAT digital print was photoreduced to a film positive at the same scale as the U-2 film and overlain on the U-2 color film. As a result of this merging technique, cover types can be identified more accurately and probablistic statements can be made about the relative amounts of water being consumed in one pasture vs. another. The hazards to urban development on sensitive and unstable land in the foothills of Davis County were studied using NASA U-2 photography. Shoreline fluctuations were mapped in the Farmington Bay using LANDSAT digital data.

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NASA NTRS1979

Solitary waves in stratified shear flows

An analysis is described of long, finite-amplitude internal waves in a stratified shear flow. Both regular and singular modes are considered with a nonlinear critical layer employed in the latter case. A three-layer model is used to develop the theory and closed-form expressions are obtained relating the phase speed to the Richardson number, the latter quantity being taken as O(1). The amplitude evolution equation is found to be either the Korteweg-de Vries equation or the Benjamin-Davis-Ono equation depending upon the distance of the more remote boundary from the edge of the shear layer.

Maslowe, S. A.↗

NASA NTRS1980

The collective excitation of g-modes in the sun

Oscillations of the solar interior (linear g-modes) may be strongly driven by the collective influence of all the modes upon the nuclear reactions in the core. This heretofore neglected effect could couple the modes, reduce the effective amplitudes near the center, and spatially concentrate most of the oscillation energy into just a portion of the radiative interior. If operating at sufficient strength, this can reverse the conventional conclusion, drawn from single mode calculations, that almost all solar g-modes are damped. Furthermore, it would put the theory into rough harmony with three otherwise troubling observations: (1) the 'low' neutrino flux measured by Davis (1978), (2) the high correspondence found by Wolff (1976) between recurrence periods in solar activity and the rotational beat periods of g-modes, and (3) the fluctuations in the sun's diameter which imply g-mode activity at high angular harmonics (Hill and Caudell 1979). A nonlinear expression is derived for the local rate of work done on an array of oscillation modes by the nuclear reactions. Three additional tests of the model are suggested.

Wolff, C. L.↗

NASA NTRS1980

Similarity solutions of some two-space-dimensional nonlinear wave evolution equations

Similarity reductions of the two-space-dimensional versions of the Korteweg-de Vries, modified Korteweg-de Vries, Benjamin-Davis-Ono, and nonlinear Schroedinger equations are presented, and some solutions of the reduced equations are discussed. Exact dispersive solutions of the two-dimensional Korteweg-de Vries equation are obtained, and the similarity solution of this equation is shown to be reducible to the second Painleve transcendent.

Redekopp, L. G.↗