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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2009

Radial and Solar Cycle Variations of the Magnetic Fields in the Heliosheath: Voyager 1 Observations from 2005 to 2008

We discuss the magnetic field strength B(t) and polarity observed by Voyager 1 (V1) in the heliosheath at the heliographic latitude approximately equal 34 deg as it moved away from the sun from 2005 through 2008.82. The pattern of the polarity of the magnetic field changed from alternating positive and negative polarities to predominantly negative polarities (magnetic fields pointing along the Archimedean spiral field angle toward the sun) at approximately equal 2006.23). This transition indicates that the latitudinal extent of the heliospheric current sheet (HCS) was decreasing in the supersonic solar wind, as expected for the declining phase of the solar cycle, and as predicted by extrapolation of the magnetic neutral line near the photosphere to the position of V1. However, the polarity was not uniformly negative in during 2008, in contrast to the predicted polarity. This difference suggests that the maximum latitudinal extent of the HCS was tending to increase in the northern hemisphere in the heliosheath, while it was decreasing in the supersonic solar wind. The large-scale magnetic field strength B(t) HCS was observed by V1 from 2005 through 2008.820. During this interval of decreasing solar activity toward solar minimum, B(t) at 1 AU was decreasing and the solar wind speed V at the latitude of V1 was increasing. Adjusting the temporal profile of B(t) observed by V1 for the solar cycle variations of B and V in the supersonic solar wind, we find that the radial gradient of B(R) in heliosheath from the radial distance R = 94.2 AU to 107.9 AU between 2005.0 and 2008.82 was 0.0017 nT/AU <= grad B <= 0.0055 nT/AU or grad B = (0.0036 +/- 0.0019) nT/AU

Burlaga, Leonard↗
NASA NTRS1977

Observations of neutral composition and related ionospheric variations during a magnetic storm in February 1974

The neutral-atmosphere composition experiment on Atmosphere Explorer C measured N2, O, Ar, and He densities during a magnetic storm at altitudes down to about 160 km. At latitudes above 45 deg N, N2 and Ar densities generally increase during the storm, while He and O densities decrease. Below 45 deg N all densities tend to increase during the storm. The density increases at perigee indicate that density- or temperature-profile changes are taking place below 160 km. The return to prestorm conditions is very slow, demonstrating the integrating effect of the atmospheric response. A recent theoretical model incorporating thermospheric circulation and diffusion effects reproduces the longitudinally averaged data, including latitude trends and the asymmetry about the storm maximum. Comparison with the mass-spectrometer and incoherent-scatter empirical model shows qualitative agreement with latitude trends but not with storm asymmetry, while the earlier J71 model based on total mass density is not in agreement with observed latitudinal trends. A close correlation is found between in situ O/N2 measurements and in situ and ground-based ionosonde measurements of electron density.

Hedin, A. E.↗
NASA NTRS1988

Systematic variation of magnetic-field penetration depth in high-T(c) superconductors studied by muon spin relaxation

The muon relaxation rate (sigma) was measured in the high critical temperature superconductors YBa2Cu3O(x) for x = 6.66, 6.95, 7.0, and La1.85 Sr0.15 CuO4 in transverse external magnetic fields 1 is approximately 4kG. A simple relation is found which connects the transition temperature T(c), the magnetic field penetration depth lambda(L), the carrier concentration n(s) and the effective mass m* as T(c) varies as sigma which varies as 1/lambda(L) squared which varies as n(s)/m*. The linear dependence T(c) varies as n(s)/m* suggests a high energy scale for the coupling between superconducting carriers.

Uemura, Y. J.↗
NASA NTRS1988

Systematic variation of magnetic-field penetration depth in high-Tc superconductors studied by muon-spin relaxation

The muon relaxation rate (sigma) was measured in the high critical temperature superconductors YBa2Cu3O(x) for x = 6.66, 6.95, 7.0, and La1.85 SrO.15 CuO4 in transverse external magnetic fields 1 is approximately 4 kG. A simple relation is found which connects the transition temperature T(c), the magnetic field penetration depth lambda(L), the carrier concentration n(s) and the effective mass m* as T(c) varies as sigma which varies as 1/lambda(L) squared which varies as n(s)/m*. The linear dependence T(c) varies as n(s)/m* suggests a high energy scale for the coupling between superconducting carriers.

Uemura, Y. J.↗
NASA NTRS1992

Topological variation in the magnetic field line at the dayside magnetopause

This paper uses normal mode analysis to examine topological changes in magnetic field lines at the magnetopause. For a modified Harris sheet, the normal modes include a symmetric solution (tearing mode) and an antisymmetric solution (twisting mode). Both modes form flux ropes. The tearing mode in the presence of shear flow is studied. By modeling the external region plasma with drift kinetic formalism, the growth rate of the tearing mode is found to be reduced by shear flow. On the other hand, the shear flow generates a Kelvin-Helmholtz instability which makes the magnetic field perturbation a twisting mode structure. When magnetopause parameters are used, it is difficult to induce a tearing mode in the presence of shear flow, though a shear flow twisting mode did grow under these conditions.

Wang, Zhi↗
NASA NTRS1993

Long-term variations of interplanetary magnetic field spectra with implications for cosmic ray modulation

The paper calculates yearly averaged power spectra of interplanetary magnetic field turbulence at 1 AU over the period 1965-1988 for fluctuations in the frequency range 5.8 x 10 exp -6 to 4.6 x 10 exp -5 Hz, corresponding to periods of 6-48 hr. The amplitudes of the spectra vary with the sunspot cycle and are inversely correlated with the intensity of about 10-GeV cosmic rays. The observed spectra are used to calculate a lower limit to the cosmic ray scattering mean free path employing resonant magnetostatic quasi-linear theory for both 'slab' and isotropic geometries of the turbulence. The mean free paths thus obtained are typically about 0.1 AU in the slab model and about 0.3 AU in the isotropic model, but they are not significantly correlated with the modulated galactic cosmic ray intensity recorded by neutron monitors. It is inferred that the scattering processes described by resonant magnetostatic theory play, at best, a very minor role in the solar modulation of about 10-GeV cosmic rays.

Bieber, John W.↗
NASA NTRS1983

Estimation of lower crust magnetization form satellite derived anomaly field

Various lines of evidence point to the lower crust as the source of the long-wavelength magnetic anomaly field measured by the POGO and Magsat satellites. Using seismically determined lower crust thicknesses and equivalent source inversion of the satellite anomaly data, magnetization for the lower crust for much of the United States has been calculated. The average magnetization for two hundred sixty-six 150 x 150 km areas is 3.5 A/m with a standard deviation of 1.1 A/m. These values are consistent with laboratory measurements of mafic-ultramafic rocks expected in the lower crust, and in agreement with previous estimates of lower crust magnetization based on long-wavelength aeromagnetic data. Average lower crust thickness for the same areas is 18.2 km (sigma = 6.4). Thus, over large regions, it appears that variation in magnetization and variation in magnetic layer thickness contribute almost equally in causing the anomaly field variation at satellite altitude.

Schnetzler, C. C.↗
NASA NTRS2010

Interplanetary Magnetic Field Power Spectrum Variations: A VHO Enabled Study

The newly reprocessed high time resolution (11/22 vectors/sec) Wind mission interplanetary magnetic field data and the solar wind key parameter search capability of the Virtual Heliospheric Observatory (VHO) affords an opportunity to study magnetic field power spectral density variations as a function of solar wind conditions. In the reprocessed Wind Magnetic Field Investigation (MFI) data, the spin tone and its harmonics are greatly reduced that allows the meaningful fitting of power spectra to the approx.2 Hz limit above which digitization noise becomes apparent. The power spectral density is computed and the spectral index is fitted for the MHD and ion inertial regime separately along with the break point between the two for various solar wind conditions . The time periods of fixed solar wind conditions are obtained from VHO searches that greatly simplify the process. The functional dependence of the ion inertial spectral index and break point on solar wind plasma and magnetic field conditions will be discussed

Szabo, A.↗
NASA NTRS2011

Interplanetary Magnetic Field Power Spectrum Variations: A VHO Enabled Study

The newly reprocessed high time resolution (11/22 vectors/sec) Wind mission interplanetary magnetic field data and the solar wind key parameter search capability of the Virtual Heliospheric Observatory (VHO) affords an opportunity to study magnetic field power spectral density variations as a function of solar wind conditions. In the reprocessed Wind Magnetic Field Investigation (MFI) data, the spin tone and its harmonics are greatly reduced that allows the meaningful fitting of power spectra to the ~2 Hz limit above which digitization noise becomes apparent. The power spectral density is computed and the spectral index is fitted for the MHD and ion inertial regime separately along with the break point between the two for various solar wind conditions. The time periods of fixed solar wind conditions are obtained from VHO searches that greatly simplify the process. The functional dependence of the ion inertial spectral index and break point on solar wind plasma and magnetic field conditions will be discussed

Szabo, A.↗