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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 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Three-dimensional numerical simulation of interplanetary magnetic field changes at 1 AU as a consequence of simulated solar flares

In order to study the relationship between different forms of activity and transient variations of the north-south component, B(sub z), of the Interplanetary Magnetic Field (IMF), at 1 AU, a three dimensional numerical simulation code was employed to study several aspects of this problem. One form of solar activity, the flare, is simulated by using a pressure pulse at different locations near the solar surface and observing the simulated IMF evolution of B(sub theta)(-B(sub z)) at 1 AU. It was found, for a given pressure pulse, that the orientation of the corresponding transient variation of B(sub z) has a strong relationship with the location of the pressure pulse and the initial condition of IMF.

Wu, S. T.↗
NASA NTRS1972

Electric field variations during substorms: OGO-6 measurements

The OGO-6 electric field measurements make it clear that the general pattern of high latitude electric fields in magnetic time-invariant latitude coordinates is not highly variable and that when unusual variations, or field distributions, occur they are relatively isolated in time and spatial extent. Thus, electric field changes on a global scale cannot, in general, be evoked as a direct cause of substorms. Polar traverses along the 18(h) to 6(h) magnetic time meridian show that the sum of potential drops across the evening auroral belt and morning auroral belt approximately equals the potential drop across the polar cap. The integrated polar cap potential drop ranges from 20 to 100 keV and values in the center of this range are most common under conditions of moderate magnetic disturbance. Roughly near 18(h) magnetic local time, a latitudinally narrow strip at the transition between auroral belt and polar cap fields exhibits unusually large field fluctuations immediately following the sudden onset of a negative bay at later magnetic local times. It appears likely that this spatially isolated correlation is related to an effect rather than a cause of substorm enhancement.

Heppner, J. P.↗
NASA NTRS1986

Observations of the interactions of heavy ions from Comet P/Giacobini-Zinner with the solar wind

During the encounter between the ICE spacecraft and Comet Giacobini-Zinner, intense fluxes of energetic heavy ions were observed up to 4 x 10 to the 6th km from the comet. In this paper the authors correlated observations of heavy ions, the solar wind velocity and the magnetic field direction, and compare the observations of the ions with the theoretical predictions for their variations with distance from the comet, wih the solar wind velocity and with the magnetic field direction.

Sanderson, T. R.↗
NASA NTRS1991

The sun's luminosity over a complete solar cycle

The Active Cavity Radiometer Irradiance Monitor (ACRIM I) measured the sun's luminosity from early 1980 to late 1989. The first account of the complete ACRIM I data set is presented and evidence is given which confirms that solar luminosity varies with the 11-yr solar cycle. This slow variation closely follows statistical measures of the distribution of magnetic and photospheric features on the solar surface. An exception to this correlation occurred in the form of a remarkable irradiance excess during 1980, at about the time of the sunspot maximum of solar cycle 21. The linkage, over a whole cycle, of luminosity variation to photospheric activity suggests the existence of an unknown physical mechanism other than the thermal diffusion model that explains luminosity deficits due to sunspots. Luminosity models connecting total irradiance to global indicators of solar activity are consistent with the gross features of the variability but fail to account for the 1980 irradiance excess.

Willson, Richard C.↗
NASA NTRS1991

Influence of a magnetic field during directional solidification of MAR-M 246 + Hf superalloy

An area that has been almost totally overlooked in the optimization of properties in directionally solidified superalloys is the control of microstructural features through the application of a magnetic field during solidification. The influence of a magnetic field on the microstructural features of a nickel-base superalloys is investigated. Studies were performed on the dendritic MAR-M 246+Hf alloy, which was solidified under both a 5 K gauss magnetic field and under no-applied-field conditions. The possible influences of the magnetic field on the solidification process were observed by studying variations in microstructural features including volume fraction, surface area, number, and shape of the carbide particles. Stereological factors analyzed also included primary and secondary dendrite arm spacing and the volume fraction of the interdendritic eutectic constituent. Microprobe analysis was performed to determine the chemistry of the carbides, dendrites, and interdendritic constituents, and how it varied between field and no-field solidification samples. Experiments involving periodic application and removal of the magnetic field were also performed in order to permit a comparison with structural variations observed in a MAR-M 246+Hf alloy solidified during KC-135 high-g, low-g maneuvers.

Andrews, J. Barry↗
NASA NTRS1977

Feige 7 - A hot, rotating magnetic white dwarf

Results are reported for image-tube-scanner and digicon observations of Feige 7, a faint blue star identified as a probable white dwarf. It is found that this star is a magnetic white dwarf showing a very rich spectrum with Zeeman subcomponents of both hydrogen and neutral helium as well as periodic spectrum and circular-polarization variations. A polarization period of 2.2 hr is computed, and a surface magnetic-field strength of about 18 MG is determined by matching features of the absorption spectrum to Zeeman components. It is suggested that the only reasonable explanation for the periodic variations in circular polarization is an oblique rotator with the spin axis approximately in the plane of the sky and tilted by about 24 deg to the magnetic axis. An effective temperature in the range from 20,000 to 25,000 K is estimated, an absolute magnitude of about 10.5 is derived, and the atmosphere is shown to be helium-dominated. The evolution of Feige 7 is discussed in terms of possible magnetic-field effects on atmospheric composition, rotation velocity (5.5 km/s for a radius of 7000 km), and the origin of white-dwarf magnetic fields.

Liebert, J.↗
NASA NTRS1988

Modelling a C-type flare observed in microwaves and hard X-rays

Using the very large array (VLA) at 6 and 20 cm wavelength and the hard X-ray burst spectrometer on the Solar Maximum Mission, a two-ribbon flare was observed from the onset phase through the maximum and decline on November 14, 1981. Because of the extensive size of the microwave source and the gradual variations in hard X-rays whose spectrum becomes progressively flatter with time, the flare is classified as a C-type flare. Considering the hardening of the X-ray spectrum and its non-impulsive nature, a coronal trap model was invoked for the energetic electrons. The microwave emission is easily accounted for by gyrosynchronous radiation from mildly relativistic electrons. It was found that the source must be optically thick at 20 cm during the maximum phase, but as the source evolved toward an optically thin regime, the intensity decreased while the degree of circular polarization increased. In an initial homogeneous model, we found that the computed microwave spectrum was too narrow to match the patrol spectrum from 606 to 15400 MHz. In the model, the magnetic field consists of a dipolar arcade bridging the H alpha ribbons, and extending to heights of order 40,000 to 50,000 km. The variation of the magnetic field strength from footpoints to apex causes the gyrosynchrotron spectrum to be broader. Preliminary conclusions regarding the electron distributions producing the hard X-rays and the microwaves, and the suitability of this model for C-type flares is presented.

Schmahl, E. J.↗
NASA NTRS1999

Test Status for Proposed Coupling of a Gravitational Force to Extreme Type II YBCO Ceramic Superconductors

As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair electron density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (about 10-6 g/cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with the percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 10(exp 4) was reported above a stationary (non-rotating) superconductor. In the present experiments reported using a sensitive gravimeter (resolution <10(exp -9) unit gravity or variation of 10(exp -6) cm/sq s in accelerations), bulk YBCO superconductors were stably levitated in a DC magnetic field (0.6 Tesla) subject to lateral AC fields (60 Gauss at 60 Hz) and rotation. With magnetic shielding, thermal control and buoyancy compensation, changes in acceleration were measured to be less than 2 parts in 10(exp 8) of the normal gravitational acceleration. This result puts new limits on the strength and range of the proposed coupling between high-Tc superconductors and gravity. Latest test results will be reported, along with status for future improvements and prospects.

Noever, David↗
NASA NTRS1976

Solar cycle review /General aspects/

Several topics are discussed in this review of the solar cycle. The basic solar-interplanetary magnetic structure is considered, and the high speed solar wind streams and their sunspot cycle variation are described, with attention to the sunspot cycle variation, the high speed solar wind streams and geomagnetic disturbances, and the causes of changes of the north-south component of the interplanetary magnetic field. Solar storms, solar flares, and magnetic bubbles are examined with attention directed to the solar cycle variation of transient polar activities and the interplanetary disturbances associated with solar storms. Some features of cosmic rays, the 11-year cycle variation and the Forbush decreases, are considered. Attention is also directed to the terrestrial atmosphere and to the outer planets and their relation to the solar cycle.

Akasofu, S.-I.↗
NASA NTRS1993

Transient magnetic field signatures at high latitudes

We survey GOES 2/5/6 geosynchronous and Huancayo, Peru, ground magnetometer observations at the times of 70 transient (2-10 min) events recorded at South Pole Station, Antarctica. The simultaneous observations indicate that most South Pole events correspond to sudden sharp variations in the equatorial magnetospheric and low-latitude ground magnetic field. The exceptions occur when the South Pole events have weak amplitudes and/or Huancayo and GOES 2/5/6 are far from local noon. The corresponding features observed at GOES 5 and GOES 6 are generally similar, with a lag indicating antisunward motion. A similar antisunward motion may be inferred from the ground observations themselves. On a case-by-case and statistical basis, the characteristics of the events observed in South Pole ground magnetograms resemble those previously interpreted as sudden impulse and sudden storm commencement signatures at other high-latitude stations. These observations suggest that the transient events at South Pole form part of the magnetospheric and ionospheric response to a sudden change in the fraction of the solar wind dynamic pressure applied to the magnetosphere.

Sibeck, D. G.↗
NASA NTRS2011

Effect of Cross-Correlation on Geomagnetic Forecast Accuracies

Surface geomagnetic observation can determine up to degree L = 14 time-varying spherical harmonic coefficients of the poloidal magnetic field. Assimilation of these coefficients to numerical dynamo simulation could help us understand better the dynamical processes in the Earth's outer core, and to provide more accurate forecast of geomagnetic secular variations (SV). In our previous assimilation studies, only the poloidal magnetic field in the core is corrected by the observations in the analysis. Unobservable core state variables (the toroidal magnetic field and the core velocity field) are corrected via the dynamical equations of the geodynamo. Our assimilation experiments show that the assimilated core state converges near the CMB, implying that the dynamo state is strongly constrained by surface geomagnetic observations, and is pulled closer to the truth by the data. We are now carrying out an ensemble of assimilation runs with 1000 years of geomagnetic and archeo/paleo magnetic record. In these runs the cross correlation between the toroidal and the poloidal magnetic fields is incorporated into the analysis. This correlation is derived from the physical boundary conditions of the toroidal field at the core-mantle boundary (CMB). The assimilation results are then compared with those of the ensemble runs without the cross-correlation, aiming at understanding two fundamental issues: the effect of the crosscorrelation on (1) the convergence of the core state, and (2) the SV prediction accuracies. The constrained dynamo solutions will provide valuable insights on interpreting the observed SV, e.g. the near-equator magnetic flux patches, the core-mantle interactions, and possibly other geodynamic observables.

Kuang, Weijia↗
NASA NTRS1981

Spherical-earth Gravity and Magnetic Anomaly Modeling by Gauss-legendre Quadrature Integration

The usefulness of long-wavelength potential field anomalies in lithospheric interpretation is greatly increased with spherical Earth modeling techniques. Gauss-Legendre quadrature integration is used to calculate the anomalous potential of gravity and magnetic fields and their spatial derivatives on a spherical Earth for an arbitrary body represented by an equivalent point source distribution of gravity poles or magnetic dipoles. The distribution of equivalent point sources is determined directly from the coordinate limits of the source volume. Variable integration limits for an arbitrarily shaped body are derived from interpolation of points which approximate the body's surface envelope. The versatility of the method is enhanced by the ability to treat physical property variations within the source volume and to consider variable magnetic fields over the source and observation surface. A number of examples verify and illustrate the capabilities of the technique, including preliminary modeling of potential field signatures for Mississippi embayment crustal structure at satellite elevations.

Spherical coordinate gravity modeling↗
NASA NTRS1979

The effect of magnetic fields on solar luminosity

The paper presents an investigation into the influence of magnetic fields in sunspots and faculae on solar luminosity, using measurements of the solar constant from ground level and from space. Attention is given to an analysis that shows that it is difficult to devise an atmospheric mechanism that would rapidly lower visible and infrared transmission in response to sunspots, increase it in response to faculae, and anticipate the magnetic development of these features by about one day. It is shown that the phase shift of the luminosity variation provides a promising new technique to determine the depth at which the magnetic fields of sunspots and faculae redistribute the flow of convective energy.

Foukal, P.↗
NASA NTRS1981

Phase space variations of near equatorially mirroring ring current ions

Observations of near equatorially mirroring ring current ions before and after a magnetic storm are presented in the form of phase space densities with respect to the first adiabatic invariant. Particle densities were obtained from the medium energy particles instrument covering the energy range 24-2081 keV on ISEE 1 at L values between 3 and 8 earth radii and ratios of the magnetic field at the satellite position to the magnetic field at the magnetic equator less than 1.2. Analysis of the phase space densities through the magnetosphere reveals a well-defined high magnetic moment peak in the prestorm near-equatorial ring current ion phase space density distribution, with the magnetic storm resulting from an enhancement of phase space densities at magnetic moment values below the peak and phase space densities remaining constant above the peak. Results are found to be in good agreement with those obtained by Explorer 45 six years previously, indicating that the observed phase space density variations are characteristic of energetic ion behavior during magnetic storms.

Williams, D. J.↗
NASA NTRS1985

Solar activity beyond the disk and variations of the cosmic ray gradient

Part of galactic cosmic rays (CR) observed near the Earth and on the Earth come from beyond-disk regions of circumsolar space. But CR of those energies which undergo substantial modulation cover too large a path across the lines of force of the interplanetary magnetic field (IMF) in order that they could provide an effective transfer of information about beyond-disk solar activity. And if it is still possible, the most probable channel for transferring such information must be a neutral layer of heliomagnetosphere in which the transverse CR transport is facilitated by their drift in an inhomogeneous magnetic field. A simple diffusion model for an expected CR variation in a neutral layer near the Earth is discussed. It is of importance that variations of the CR gradient are not at all always accompanied by considerable variations of IMF and solar wind velocity at the point of observation.

Belov, A. V.↗
NASA NTRS1981

Spherical-earth gravity and magnetic anomaly modeling by Gauss-Legendre quadrature integration

Gauss-Legendre quadrature integration is used to calculate the anomalous potential of gravity and magnetic fields and their spatial derivatives on a spherical earth. The procedure involves representation of the anomalous source as a distribution of equivalent point gravity poles or point magnetic dipoles. The distribution of equivalent point sources is determined directly from the volume limits of the anomalous body. The variable limits of integration for an arbitrarily shaped body are obtained from interpolations performed on a set of body points which approximate the body's surface envelope. The versatility of the method is shown by its ability to treat physical property variations within the source volume as well as variable magnetic fields over the source and observation surface. Examples are provided which illustrate the capabilities of the technique, including a preliminary modeling of potential field signatures for the Mississippi embayment crustal structure at 450 km.

Von Frese, R. R. B.↗
NASA NTRS1973

Magnetic storm characteristics of the thermosphere.

Energy and diffusive mass transport associated with the thermospheric circulation are considered in a self-consistent, though mathematically relatively simple, form to describe in a three-dimensional two-constituent model magnetic storm characteristics in composition (N2, O, and He), temperature, and mass-density. It is shown that during disturbed conditions the latitudinal variations of composition and gas temperature reflect the local nature of the magnetic storm heat input assumed to be primarily confined to the auroral zones. Thereby gas temperature and N2 increase, He decreases, and O remains constant through the auroral zones at exospheric heights (due to the superposition of temperature and diffusion effects) in agreement with Ogo 6 mass spectrometer measurements. In contrast, the magnetic storm response in the total mass density is characterized by a strong worldwide component and a relatively insignificant increase toward the poles.

Mayr, H. G.↗