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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 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Plasma and energetic electron flux variations in the Mercury 1 C event - Evidence for a magnetospheric boundary layer

Charge-particle and magnetic-field data obtained during the first encounter (on March 29, 1974) of Mariner 10 with the planet Mercury are reexamined, and a new interpretation of the Mariner 10 energetic electron, plasma electron, and magnetic field data near the outbound magnetopause at Mercury is presented. It is shown that Mariner 10 sampled the hot substorm energized magnetospheric plasma sheet for the first 36 sec of the C event and, for the next 48 sec, alternatively sampled hot (plasma sheet) and cold (boundary-layer magnetosheathlike) plasma regions. It is argued that the counting rate of the ID1 event (i.e., a particle event triggering detector D1 but not the D2, D3, or D7 detectors) throughout the C event most probably represents a pulse pileup response to about 35-175 keV electrons, rather than the nominal above-175 keV electrons presumed in the earlier interpretations.

Christon, S. P.↗
NASA NTRS1998

Global Ionospheric TEC Variations During January 10, 1997 Storm

The ionospheric storm evolution process was monitored during the January 10, 1997 magnetic cloud event, through measurements of the inonospheric total electron content (TEC) from 150 GPS stations. The first significant response of the inonospheric TEC to the geomagnetic storm was at 0300 UT as an auroral/subauroral enhancement around the Alaskan evening sector.

Global Ionospheric TEC ionospheric storm magnetic ↗
NASA NTRS1994

On the maximum energy release in flux-rope models of eruptive flares

We determine the photospheric boundary conditions which maximize the magnetic energy released by a loss of ideal-magnetohydrodynamic (MHD) equilibrium in two-dimensional flux-rope models. In these models a loss of equilibrium causes a transition of the flux rope to a lower magnetic energy state at a higher altitude. During the transition a vertical current sheet forms below the flux rope, and reconnection in this current sheet releases additional energy. Here we compute how much energy is released by the loss of equilibrium relative to the total energy release. When the flux-rope radius is small compared to its height, it is possible to obtain general solutions of the Grad-Shafranov equation for a wide range of boundary conditions. Variational principles can then be used to find the particular boundary condition which maximizes the magnetic energy released for a given class of conditions. We apply this procedure to a class of models known as cusp-type catastrophes, and we find that the maximum energy released by the loss of equilibrium is 20.8% of the total energy release for any model in this class. If the additional restriction is imposed that the photospheric magnetic field forms a simple arcade in the absence of coronal currents, then the maximum energy release reduces to 8.6%

Forbes, T. G.↗
NASA NTRS1979

Origin of the magnetic fields in the giant planets

The paper discusses origin of the magnetic fields in the giant planets. Recent data on the generation of these fields provide conclusions on giant planets; the Jovian magnetic field can be of primordial origin or generated by a thermally driven dynamo, and the expected Saturnian field can be accounted for thermally or by a precessionally driven dynamo. The presence of a 0.1 gauss field on Uranus presents a problem because the so far unobserved thermal flux and convection may be too low, and if such a dynamo were to operate then the field should show seasonal variations. A conductive shell on Neptune similar to that on Uranus appears to be much thinner, but it is likely that Neptune has a magnetic field which is too weak to lead to observable electromagnetic variations.

Smoluchowski, R.↗
NASA NTRS1990

Elementary bipoles of active regions and ephemeral active regions

The general properties of elementary bipoles (EBs), the class of moving magnetic features identified by Frazier (1972) as building blocks of new solar active regions, are described, and variations in their characteristics are illustrated with extensive videomagnetograms obtained at Big Bear Solar Observatory during 1984-1989. Consideration is given to ephemeral active regions consisting of EBs with only one positive and one negative pole, multiple-pole ephemeral regions, reversed-polarity EBs, interactions among EBs and adjacent magnetic features, and the EBs of small and medium active regions. The detection of EBs prior to the appearance of arch filaments confirms the relationship found by Frazier.

Martin, Sara F.↗
NASA NTRS1982

Development of photomultiplier electronics and computer interfacing software for a high speed photoelectric photometer-Stoke's meter

Preliminary stages in the design, construction, and development of a photoelectric photometer system interfaced with an IMSAI 8080 microcomputer. The instrument will also include magnetic tape and magnetic disk storage capabilities to enable rapid data storage. The capability of the instrument to make observations with very high time resolution, as high as 10 msec, and measure the intensity and polarization of radiation emitted by objects which show very rapid light variations, pulsars and optical counterparts of X-ray sources was of concern. A better understanding of the magnetic fields and interstellar material which characterize the immediate environment of these stellar systems and an expansion of the observational capabilities of even modest-sized telescopes are expected.

Flesch, T. R.↗
NASA NTRS1991

A two-dimensional, time-dependent, near-earth magnetotail

A kinetic approach is presented for obtaining slowly time-dependent, self-consistent plasma, and magnetic field configurations for this region, using anisotropic particle distributions. At present, a 2D configuration is used. The time variation of the plasma/field configuration is assumed to be driven by a slowly varying, externally imposed electric field (representing, for example, a change in solar wind conditions). The numerical approach involves solving a 2D nonlinear Poisson equation for the magnetic vector potential at each time step. The local current density is calculated from particle velocity distributions under the assumption of adiabatic particle motion. The obtained equations of state are compared with those of double-adiabatic theory. Numerical examples of self-consistent responses of the near-earth plasma and field to an externally imposed electric field pulse are presented.

Whipple, Elden↗
NASA NTRS1995

Neptune radio emission in dipole and multipole magnetic fields

We study Neptune's smooth radio emission in two ways: we simulate the observations and we then consider the radio effects of Neptune's magnetic multipoles. A procedure to deduce the characteristics of radio sources observed by the Planetary Radio Astronomy experiment minimizes limiting assumptions and maximizes use of the data, including quantitative measurement of circular polarization. Study of specific sources simulates time variation of intensity and apparent polarization of their integrated emission over an extended time period. The method is applied to Neptune smooth recurrent emission (SRE). Time series are modeled with both broad and beamed emission patterns, and at two frequencies which exhibit different time variation of polarization. These dipole-based results are overturned by consideration of more complex models of Neptune's magnetic field. Any smooth emission from the anticipated auroral radio source is weak and briefly observed. Dominant SRE originates complex fields at midlatitude. Possible SRE source locations overlap that of 'high-latitude' emission (HLE) between +(out) and -(in) quadrupoles. This is the first identification of multipolar magnetic structure with a major source of planetary radio emission.

Sawyer, C. B.↗
NASA NTRS2000

Suppression/Reversal of Natural Convection by Exploiting the Temperature/Composition Dependence of Magnetic Susceptibility

Natural convection, driven by temperature-or concentration gradients or both, is an inherent phenomenon during solidification of materials on Earth. This convection has practical consequences (e.g effecting macrosegregation) but also renders difficult the scientific examination of diffusive/conductive phenomena during solidification. It is possible to halt, or even reverse, natural convection by exploiting the variation (with temperature, for example) of the susceptibility of a material. If the material is placed in a vertical magnetic field gradient, a buoyancy force of magnetic origin arises and, at a critical field gradient, can balance the normal buoyancy forces to halt convection. At higher field gradients the convection can be reversed. The effect has been demonstrated in experiments at Marshall Space Flight Center where flow was measured by PIV in MnCl2 solution in a superconducting magnet. In auxiliary experiments the field in the magnet and the properties of the solution were measured. Computations of the natural convection, its halting and reversal, using the commercial software FLUENT were in good agreement with the measurements.

Seybert, C. D.↗
NASA NTRS1974

Heating of the high-latitude thermosphere during magnetically quiet periods

A persistent mid- to high-latitude heating phenomenon is observed in both hemispheres in data from the Ogo 6 quadrupole mass spectrometer. The phenomenon is evidenced by an increase in N2 density (indicative of a thermospheric temperature rise) and a depletion in helium (indicating an upwelling of air). The composition changes maximize near 0900 and 2100 UT, appear to corotate with the local magnetic pole, and are larger near equinox than near the summer solstice. The variation in latitude of the peak in the winter helium density (as a function of UT) is a specific manifestation of this general heating phenomenon.

Reber, C. A.↗
NASA NTRS1981

Magnetic transients in flares

Data are presented on magnetic transients (mgtr's) observed in flares on July 1 and 5, 1980, with Big Bear videomagnetograph. The event of July 1 was a white light flare in which a strong bipolar mgtr was observed and a definite change in the sunspots occurred at the time of the flare. In the flare of July 5, a mgtr was observed in only one polarity, and although no sunspot changes occurred simultaneous with the flare, significant spot changes occurred in a period of hours. Suggestions are made as to what might be occurring in the magnetic field. It is explained why the mgtr cannot be ascribed to time variation or to emission in the lambda 5324. Attention is also given to the remarkable penumbral structure associated with the July 5 flare.

Zirin, H.↗
NASA NTRS1982

Observations of the diurnal dependence of the high-latitude F region ion density by DMSP satellites

Data from the DMSP F2 and F4 satellites for the period December 5-10, 1979, have been used to study the diurnal dependence of the high-latitude ion density at 800-km altitude. A 24-hour periodicity in the minimum orbital density (MOD) during a crossing of the high-latitude region is observed in both the winter and summer hemispheres. The phase of the variation in MOD is such that it has a minimum during the 24-hour period between 0700 and 0900 UT. Both the long-term variation of the high-latitude ion density on a time scale of days, and the orbit-by-orbit variations at the same geomagnetic location in the northern (winter) hemisphere for the magnetically quiet time period chosen, show good qualitative agreement with the diurnal dependence predicted by a theoretical model of the ionospheric density at high latitudes under conditions of low convection speeds (Sojka et al., 1981).

Sojka, J. J.↗
NASA NTRS1982

Solar calibration of stellar rotation tracers

A study of the time variability of the disk-integrated solar magnetic flux, with a view to the behavior of emission-line intensity variations observed in lower main sequence stars, has determined that solar rotation modulation of the integrated flux is present in 75% of all rotations. For observing intervals of more than twice the lifetime of the features causing rotational modulation, the correct rotation period is identified in more than 90% of all cases. The optimum time for measuring rotational modulation is the decay phase of the activity cycle, and the solar rotation period is measured with an accuracy of a few percent. The lifetime of a rotational modulation period is approximately five rotations, and a sensitivity limit of Delta S= 0.005 is found for the Vaughan et al (1981) stellar rotation measures.

Labonte, B. J.↗
NASA NTRS1986

The growth of radiative filamentation modes in sheared magnetic fields

Observations of prominences show them to require well-developed magnetic shear and to have complex small-scale structure. Researchers show here that these features are reflected in the results of the theory of radiative condensation. Researchers studied, in particular, the influence of the nominally negligible contributions of perpendicular (to B) thermal conduction. They find a large number of unstable modes, with closely spaced growth rates. Their scale widths across B show a wide range of longitudinal and transverse sizes, ranging from much larger than to much smaller than the magnetic shear scale, the latter characterization applying particularly in the direction of shear variation.

Vanhoven, Gerard↗
NASA NTRS1991

Gyro-phase effects near the storm-time boundary of energetic plasma

The nonadiabatic acceleration of plasma sheet ions during the expansion phase of substorms is examined by means of single-particle codes. It is shown that, in the near-earth plasma sheet, the gyration phase at substorm onset controls the net ion energization, as the gyro-period is locally comparable to the field variation time scale. This can yield a particularly significant decrease of the particle magnetic moment. It is accordingly argued that, via adiabatic invariant violation, the dipolarization of magnetospheric field lines can induce a 'de-trapping' of inner plasma sheet populations and, hence, give rise to short-lived precipitation enhancements over the auroral zone. As this effect depends upon cyclotron frequency, it is expected to occur at distinct latitudes for different ion species. This contrasts with nonadiabatic ion behavior further out into the geotail, which is characterized by intense perpendicular heating and a likely collective trapping.

Delcourt, D. C.↗
NASA NTRS1991

The variability of the solar diameter

It is argued here that most of the variation in observations of the solar radius of over three centuries measure properties of the sun's limb darkening function and are affected by many sources of degradation of the solar image. They do not directly measure a true solar radius. From a long series of visual observations made by a single observer as well as recent photoelectric observations, evidence is found for periodicities in the apparent radius that occur in both modern and historical records. The magnitude of the observed variations is quite different in visual and photoelectric observations, suggesting that the process responsible for the periodicities is either one that modifies the solar limb darkening function or one that causes systematic variations in image blurring by the earth's atmosphere. A connection between solar magnetic activity an apparent radius seems likely, with evidence for such a relation dating back as fast as the Maunder minimum.

Ribes, E.↗