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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Average high latitude magnetic field: Variations with interplanetary sector and with season. 2: Comparison of disturbance levels and discussion of ionospheric currents

Average high latitude magnetic field data from northern observatories are examined for three ranges of magnetic disturbance level, Kp = 1 minus to 1+,2 minus to 3+, and or = 4 minus. Except for 0-8h MLT, 55-78 deg invariant latitude, during away interplanetary magnetic field sectors, the variations between season and sector have the the same characteristics at all Kp ranges. Because the amplitude of sector differences is much larger at sunlit local times than in the midnight sector, it is concluded that the current system of Svalgaard (1973) is not adequate to describe the sector variations in magnetic disturbance, other current systems are discussed briefly. The disturbance morphology and seasonal variation at all Kp levels confirms the results of previous studies which indicate that latitudinally broad current systems and non-ionospheric sources are present in addition to latitudinally narrow electrojet currents. Comparison of data between Kp levels indicates that the Harang discontinuity shifts toward earlier MLT with increasing Kp level.

Langel, R. A.↗
NASA NTRS1980

A seasonal change in the effect of field-aligned currents at synchronous orbit

The expected signature of substorm field-aligned currents is described for synchronous satellites near 10 deg magnetic latitude. The main effect is a positive D perturbation premidnight and a negative D perturbation postmidnight. This behavior is illustrated for two substorms near the fall equinox. A second pair of substorms taken from winter solstice do not show the expected behavior. The absence of this effect in winter observations is verified statistically by superposed epoch analysis. A simple explanation of this behavior based on the geometry of the plane of magnetic symmetry is presented. During disturbed times at winter solstice a synchronous satellite nominally at 10 deg magnetic latitude is effectively at the magnetic equator. This distortion of the magnetic equator must be considered in future models of the disturbed magnetospheric magnetic field.

Mcpherron, R. L.↗
NASA NTRS1975

A comparison of electric and magnetic field data from the OGO 6 spacecraft

Previous studies of OGO 6 electric-field data and magnetic-field magnitude observations have indicated a distinct dependence of disturbance characteristics on interplanetary-sector polarity. Examination of simultaneous data below 600 km over the summer polar cap shows that changes in electric-field patterns and the disturbance patterns in magnetic-field magnitude are highly correlated. This correlation extends to pattern shapes, boundary locations, and the amplitudes of the correlated quantities. In the winter hemisphere at altitudes above 800 km, correlations between boundaries exist, pattern correlations are present but not as strong as at low altitudes in summer, and amplitude correlations are essentially absent. These studies verify that below 600 km, the region of positive magnetic-field magnitude, from 2200 to 1000 magnetic local time (MLT), receives a significant contribution from both ionospheric and nonionospheric sources. Above 800 km, the nonionospheric sources dominate. These data are also consistent with the existence of a latitudinally broad current system at sunlit magnetic local times as the source of the negative-magnitude region between 1000 and 2200 MLT. In this region, broad structures in electric-field patterns and in magnetic-field magnitude patterns are highly correlated. Multiple peaks in the negative-magnitude, presumably identified with the multiple peaks in negative electric-field magnitude found by Langel (1973) in average surface data, occur when the electric-field pattern has multiple reversals near dusk.

Langel, R. A.↗
NASA NTRS1986

Spatial distributions of magnetic field fluctuations in the dayside magnetosheath

In a study that tests the hypothesis that magnetosheath magnetic fields are disturbed on plasma streamlines which are connected to the quasi-parallel bow shock, magnetometer observations from the ISEE 2 and IMP 8 spacecraft are used to investigate the dayside spatial distributions of fluctuating magnetosheath fields for different interplanetary field orientations. The results suggest that although other sources such as Kelvin-Helmholtz instabilities and flux transfer processes probably contribute to the fluctuations in the magnetosheath field, the quasi-parallel shock source is an important contributor in the dayside region.

Luhmann, J. G.↗
NASA NTRS2007

Apparent Relations Between Solar Activity and Solar Tides Caused by the Planets

A solar storm is a storm of ions and electrons from the Sun. Large solar storms are usually preceded by solar flares, phenomena that can be characterized quantitatively from Earth. Twenty-five of the thirty-eight largest known solar flares were observed to start when one or more tide-producing planets (Mercury, Venus, Earth, and Jupiter) were either nearly above the event positions (less than 10 deg. longitude) or at the opposing side of the Sun. The probability for this to happen at random is 0.039 percent. This supports the hypothesis that the force or momentum balance (between the solar atmospheric pressure, the gravity field, and magnetic field) on plasma in the looping magnetic field lines in solar corona could be disturbed by tides, resulting in magnetic field reconnection, solar flares, and solar storms. Separately, from the daily position data of Venus, Earth, and Jupiter, an 11-year planet alignment cycle is observed to approximately match the sunspot cycle. This observation supports the hypothesis that the resonance and beat between the solar tide cycle and nontidal solar activity cycle influences the sunspot cycle and its varying magnitudes. The above relations between the unpredictable solar flares and the predictable solar tidal effects could be used and further developed to forecast the dangerous space weather and therefore reduce its destructive power against the humans in space and satellites controlling mobile phones and global positioning satellite (GPS) systems.

Hung, Ching-Cheh↗
NASA NTRS1982

Correlated Birkeland current signatures from the TRIAD and Magsat magnetic field data

Transverse magnetic disturbances associated with Birkeland currents have been measured by the Magsat and TRIAD spacecraft, whose orbits were nearly coplanar from November to mid-December, 1979. A comparison of data received when the satellites were over the TRIAD/Chatanika receiving station shows that 75% of magnetic disturbance measurements are similar in shape and magnitude, with TRIAD peak disturbances being on average 7% larger than those of Magsat. This discrepancy is lower than measurement uncertainties due to baselines and calibration. During periods of higher Kp, despite time separations of as much as 45 min, better agreement is found in the large-scale and well-defined field-aligned current signatures.

Zanetti, L. J.↗
NASA NTRS1984

Interplanetary magnetic field enhancements and their association with the asteroid 2201 Oljato

Comparison of the times of occurrence of a newly discovered type of disturbance in the interplanetary magnetic field at 0.72 astronomical unit with the passage of the small Venus-crossing asteroid, 2201 Oljato, reveals a possible association, but the source of these disturbances appears to be associated with outgassing material in the Oljato orbit some distance behind the asteroid and not with the asteroid itself. This suggested association can account for one quarter of the total number of events seen in eight Venus years.

Russell, C. T.↗
NASA NTRS1974

The relation of variations in total magnetic field at high latitude with the parameters of the interplanetary magnetic field and with DP2 fluctuations

The maximum disturbances from the positive and negative regions of delta B (Bp and Bn, respectively) are investigated with respect to their correlation with (1) the average N-S component, Bz, (2) the average angle with respect to the solar magnetospheric equatorial plane, theta (3) the variance, sigma sub i, and (4) the magnitude, Bi, of the interplanetary magnetic field. These quantities were averaged over a period, T, ranging from 20 min. to 8 hours prior to the measurement of Bp or Bn. Variations (i.e., disturbances) in total magnetic field magnitude were studied utilizing data from the Polar Orbiting Geophysical Observatory satellites (OGO 2, 4, and 6), unofficially referred to as POGO.

Langel, R. A.↗