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At least 793 records · Page 44

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NASA NTRS1978

The statistical magnetic signature of magnetospheric substorms

Daily magnetograms from a midlatitude network of geomagnetic observatories were used in the analysis of approximately 1800 substorm events, and the characteristic magnetic signatures of magnetospheric substorms both on the ground and in space were determined. Auroral electrojet (AE) indices and individual magnetograms at different local times in the auroral zone and at midlatitudes were analyzed with reference to onsets, and superposed epoch averages of individual magnetograms and AE indices confirm the local time magnetic substorm signatures. Superposed epoch averages of the interplanetary magnetic field (IMF) associated with the onsets demonstrates both a distinct southward component prior to the onsets and a dependence of the substorm amplitude on the integrated preceding southward IMF flux. Superposed epoch averages of the tail lobe magnetic field magnitude and vector components are discussed.

Caan, M. N.↗

NASA NTRS1980

A non-Fermi model of cosmic ray acceleration - The Vector-V x Vector-B

The Fermi model of cosmic ray acceleration is incomplete and frequently internally inconsistent in situations in which particles gradient B or curvature drift in a Vector-V x Vector-B electric field while interacting with moving magnetic field irregularities. In such situations particles can gain orders of magnitude more energy per reflection than predicted by the Fermi model.

Pesses, M. E.↗

NASA NTRS1981

Magnetic and gravity anomalies in the Americas

The cleaning and magnetic tape storage of spherical Earth processing programs are reported. These programs include: NVERTSM which inverts total or vector magnetic anomaly data on a distribution of point dipoles in spherical coordinates; SMFLD which utilizes output from NVERTSM to compute total or vector magnetic anomaly fields for a distribution of point dipoles in spherical coordinates; NVERTG; and GFLD. Abstracts are presented for papers dealing with the mapping and modeling of magnetic and gravity anomalies, and with the verification of crustal components in satellite data.

Braile, L. W.↗

NASA NTRS1983

The peak electromagnetic power radiated by lightning return strokes

Estimates of the peak electromagnetic (EM) power radiated by return strokes have been made by integrating the Poynting vector of measured fields over an imaginary hemispherical surface that is centered on the lightning source, assuming that ground losses are negligible. Values of the peak EM power from first and subsequent strokes have means and standard deviations of 2 + or - 2 x 10 to the 10th and 3 + or - 4 x 10 to the 9th W, respectively. The average EM power that is radiated by subsequent strokes, at the time of the field peak, is about 2 orders of magnitude larger than the optical power that is radiated by these strokes in the wavelength interval from 0.4 to 1.1 micron; hence an upper limit to the radiative efficiency of a subsequent stroke is of the order of 1 percent or less at this time.

Krider, E. P.↗

NASA NTRS1984

Active regions

The following efforts were completed in support of the Solar Maximum Mission (SMM): (1) the evolution of solar vector photospheric magnetic fields in a flare-producing active region was studied; (2) an algorithm was developed to generate maps of force-free magnetic field strengths at varying heights in the solar atmosphere; and (3) the study of the physical state of the material confined along entire magnetic loops was advanced with the use of magnetic field extrapolation.

Wu, S. T.↗

NASA NTRS1985

Solar physics applications of computer graphics and image processing

Computer graphics devices coupled with computers and carefully developed software provide new opportunities to achieve insight into the geometry and time evolution of scalar, vector, and tensor fields and to extract more information quickly and cheaply from the same image data. Two or more different fields which overlay in space can be calculated from the data (and the physics), then displayed from any perspective, and compared visually. The maximum regions of one field can be compared with the gradients of another. Time changing fields can also be compared. Images can be added, subtracted, transformed, noise filtered, frequency filtered, contrast enhanced, color coded, enlarged, compressed, parameterized, and histogrammed, in whole or section by section. Today it is possible to process multiple digital images to reveal spatial and temporal correlations and cross correlations. Data from different observatories taken at different times can be processed, interpolated, and transformed to a common coordinate system.

Altschuler, M. D.↗

NASA NTRS1986

Characteristics of the tail of Comet Giacobini-Zinner

The physical structure and characteristics of the Comet Giacobini-Zinner tail are described. Variations in the vector B-field configuration, the electron distribution function, the energetic ion population, and the electromagnetic and electrostatic plasma wave spectra are analyzed. The ICE detected a two-lobe magnetic field configuration and a narrow central plasma sheet. Additional analyses proposed for the Giacobini-Zinner tail data are discussed.

Scarf, F. L.↗

NASA NTRS1987

Equipotential transformation of multipole systems to dipole systems

The vector sum of fields produced by a set of magnetic dipoles with different magnetic moments that are both tilted from the planetary spin axis and offset from the planetary center by different amounts can be used to completely represent a planetary magnetic field in the conventional form of spherical harmonic expansion. The scalar equipotential transformation analytically results in 24 equations that may subsequently be solved for the 24 adjustable parameters in dipole systems with the predetermined main dipole. Attention is given to this method's application to the Jovian magnetic field.

Wang, W. X.↗

NASA NTRS1991

Polarization model applied to Uranian radio emission

The total power and the degree of circular polarization as measured by the Planetary Radio Astronomy experiments on the Voyager spacecraft are modeled. For a source near the electron cyclotron frequency, the degree of circular polarization is determined by the angle between the wave vector and the field. It is shown that the observed strong circular polarization of Uranian smooth low-frequency (SLF) can be modeled as emission that is beamed along the direction of the magnetic field in a filled cone. The main observational constraints of SLF emission from Uranus are met by conjugate sources at about 21 deg from the magnetic equator.

Sawyer, C. B.↗

NASA NTRS1991

Amplitude and phase-shaping effects in beamwaveguides

Results are presented of an investigation on improvements in a geometrical optics (GO) design of a beam-waveguide antenna for operation at multiple frequency bands. Improvements might be possible by changing the design of the lower-frequency input pattern to the beam waveguide. The effects of amplitude and phase shaping the input pattern have been studied with an aperture diffraction model. Accurate vector near-field computations were made rapidly with a spherical wave expansion of the input and scattered fields. Numerical results indicate that for aperture sizes of less than 30 wavelengths, there is insufficient control on defocusing due to amplitude and phase shaping. Design tradeoffs on spillover loss and defocusing are possible by changing the amplitude and phase distribution of the input wavefront for larger size apertures.

Rengarajan, Sembiam R.↗

NASA NTRS1992

Three-dimensional compressible turbulent computations for a nondiffusing S-duct

The PARC3D code was used to compute the compressible turbulent flow within a three dimensional, nondiffusing S-duct. A frame of reference is provided for future computational fluid dynamics studies of internal flows with strong secondary flows and provides an understanding of the performance characteristics of a typical S-duct with attached flow. The predicted results, obtained with both H- and O-grids, are compared with the experimental wall pressure, static and total pressure fields, and velocity vectors. Additionally, computed boundary layer thickness, velocity profiles in wall coordinates, and skin friction values are presented.

Harloff, G. J.↗

NASA NTRS1992

Navier-Stokes analysis and experimental data comparison of compressible flow in a diffusing S-duct

Full three-dimensional Navier-Stokes computational results are compared with new experimental measurements for the flowfield within a round diffusing S-duct. The present study extends previous computational and experimental results for a similar smaller scale S-duct. Predicted results are compared with the experimental static and total pressure fields, and velocity vectors. Additionally, wall pressures, velocity profiles in wall coordinates, and skin friction values are presented. The CFD results employ algebraic and k-epsilon turbulence models. The CFD computed and experimentally determined separated flowfield is carefully examined.

Harloff, Gary J.↗

NASA NTRS1992

On neutralized currents in the solar corona

Using Ampere's integral law applied to vector magnetograph transverse field data, the current pattern in an active region associated with flaring activity is analyzed. The greater sensitivity of this integral formalism of Ampere's law may allow one to identify regions of weak return current around the actual positive current region. The effects of Faraday rotation on the inferred magnetic field measurements, and hence on the deduced current pattern, are discussed. It is concluded that the current patterns in the region consist either of a neutralized current system, well modeled by a coaxial cable, or of a potential field, with the apparent currents in the core an artifact induced by magneto-optical effects. In either case, the data do not convincingly show an unneutralized current system.

Wilkinson, Ladye K.↗

NASA NTRS1992

Navier-Stokes analysis and experimental data comparison of compressible flow in a diffusing S-duct

Harloff, Gary J.↗

NASA NTRS1992

Active region studies with coordinated SOHO, microwave, and magnetograph observations

The scientific justification for an observing campaign to study the quantitative magnetic and plasma properties of coronal loops in active regions is presented. The SOHO (Solar and Heliospheric Observatory) instruments of primary relevance are CDS (Coronal Diagnostic Spectrometer), EIT, SUMER (Solar Ultraviolet Measurement of Emitted Radiation), and MDI. The primary ground based instruments would be the VLA (Very Large Array), the Owens Valley Radio Observatory, and vector and longitudinal field magnetographs. Similar campaigns have successfully been carried out with the Solar Maximum Mission x-ray polychromator and the Soft X-ray Imaging Sounding Rocket Payload (CoMStOC '87), the Goddard Solar EUV Rocket Telescope and Spectrograph, the Lockheed Solar Plasma Diagnostics Experiment rocket payload, and the Soft X-ray Telescope in Yohkoh (CoMStoc '92). The scientific payoff from such a campaign is discussed in light of the results from these previous campaigns.

Holman, Gordon D.↗

NASA NTRS1993

Navier-Stokes analysis of three-dimensional S-ducts

Full 3D Navier-Stokes computational results are presented for compressible flows within nondiffusing and diffusing S-ducts. The present study provides an understanding of the performance characteristics of typical S-ducts with attached and separated flows and provides a frame of reference for future computational fluid dynamic studies of internal flows with strong secondary flows. The predicted results, which were obtained using both H- and O-grids, are compared with the experimental wall pressures, static and total pressure fields, and velocity vectors. In addition, computed boundary-layer thickness, velocity profiles in wall coordinates and skin friction values are presented. The inviscid contributions to the secondary flows are quantified. The S-duct entrance Mach number was 0.6, and the Reynolds number was 1.76 x 10 exp 6 based on the upstream duct diameter.

Harloff, G. J.↗

NASA NTRS1994

Euler potentials of current-free fields expressed in spherical harmonics

Given a magnetic field B = -del(vector differential operator)(sub gamma) with gamma expanded in spherical harmonics, it is shown that analytic Euler potentials may be derived for B if gamma is asymmetrical but contains only the contribution of a single index n. This work generalizes a result for sectorial harmonics with n = m, derived by Willis and Gardiner (1988).

Stern, David P.↗

NASA NTRS2004

Solar Magnetic Explosions, Spicules, and the Heliosphere

We present an example of each of the following observed characteristics of the magnetic origins of quiet-region coronal heating, spicules, macrospicules, and coronal mass ejections (CMEs). (1) In quiet regions, the luminosity of the corona is roughly proportional to the edge length of the underlying photospheric magnetic network. (2) Spicules and EUV explosive events are concentrated at the edges of the magnetic network. (3) Many macrospicules have the magnetic structure of a surge rooted around an inclusion of opposite-polarity magnetic flux. (4) CMEs and eruptive flares are driven by explosions of sheared magnetic fields rooted along polarity dividing lines (neutral lines) in the photospheric magnetic flux. These characteristics together suggest that the mainstay of the heliosphere, the corona/solar wind rooted in quiet regions and coronal holes, may be driven by myriads of tiny magnetic explosions at the network edges, explosions like those that drive CMEs but of vastly smaller scale. If so, the steady solar wind and the CMEs that disrupt it both have the same root cause: explosions of initially-closed, strongly-sheared, bipolar magnetic fields. The photospheric vector magnetograms, chromospheric filtergrams, EUV spectra, and coronal images from Solar-B are expected to have sufficient sensitivity, spatial resolution, and cadence to test this scenario for coronal heating in quiet regions and coronal holes. This work was supported by NASA/OSS through its Solar and Heliospheric Physics SR and T Program and Sun-Earth Connection GI Program.

Moore, Ronald L.↗