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At least 1,495 records · Page 83
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NASA NTRS1980

The filament eruption in the 3B flare of July 29, 1973 - Onset and magnetic field configuration

The filament eruption in the large expanding two-ribbon solar flare which occurred July 29, 1973 is discussed. Observational evidence is presented for the preflare magnetic field configuration, the nature of the filament destabilization and triggering of the flare, and the magnetic field configuration after the filament eruption. The observations show that the filament is under an arcade of closed magnetic field lines prior to the eruption. The eruption of the filament and the onset of the two-ribbon H-alpha flare are preceded by precursor activity in the form of small H-alpha brightenings and mass motion along the neutral line and well below the bottom edge of the filament. The precursor H-alpha brightenings and the first brightenings in the flare ribbons are in the vicinity of the steepest magnetic field gradient in the flare region.

Moore, R. L.↗
NASA NTRS1981

Magnetic field studies by Voyager 1 - Preliminary results at Saturn

Confirmation and refinement of Saturnian magnetosphere features established by the Pioneer 11 emission are claimed for Voyager 1 magnetic field studies of the planet. The radius of the magnetopause at the subsolar point is 23 Saturn radii, and a magnetic tail of 80 Saturn radii diameter was discovered. The tail extends away from the sun and is similar to both type II comet tails and the terrestrial and Jovian magnetic tails. Data from Voyager's very close flyby of Titan, which is located within the Saturn magnetosphere, shows an absence of any substantial, intrinsic satellite magnetic field.

Ness, N. F.↗
NASA NTRS1981

Magnetic control systems for large spacecraft with applications to space telescope

Magnetic control systems for large space vehicles offer the advantage of a simple, reliable, low cost augmentation to the primary control system. When used for momentum management, a magnetic torque source offers a long life and noncontaminant environment when compared to a mass expulsion torque source. These qualities make such systems suitable for employment with the Space Telescope, which is a long life, high performance vehicle with optics and scientific instruments which would be degraded by contamination due to mass expulsion products. The various applications of magnetic systems on the Space Telescope are considered. The future trend in magnetic control of large space vehicles lies in providing a known three axis reference for backup operations, such as recovery of the primary control mode.

Dougherty, H.↗
NASA NTRS1981

X-ray and H-alpha observations of a filament-disappearance flare - An empirical analysis of the magnetic field configuration

On August, 29, 1973, a flare event occurred that involved the disappearance of a filament near central meridian. The event, well-observed in X-rays on Skylab and in H-alpha, was a four-ribbon flare involving both new and old magnetic inversion lines which were roughly parallel. The H-alpha, X-ray, and magnetic field data are used to deduce the magnetic polarities of the H-alpha brightening at the footpoints of the brightest X-ray loops. It is suggested that the event involved a reconnection of magnetic field lines rather than a brightening in place of preexisting loops. The simultaneity of the H-alpha brightening onsets in the four ribbons and the apparent lack of an eruption of the filament are consistent with this interpretation.

Kahler, S. W.↗
NASA NTRS1981

Explorer 34 magnetic field measurements near the tail current sheet and auroral activity

Explorer 34 (Imp 4) 2.56 s magnetic data obtained during 131 traversals of the tail current sheet are presented, along with the simultaneous 2.5 min auroral electrojet indices AE and AL. The normal magnetic field satellite crossing times and positions are tabulated for these 131 crossings. Normal magnetic field is defined in the center of the sheet: it is the vector magnetic field at the time of field minimum during the crossing. It is remarkable that the only normal components too large in magnitude to be classified as fine structure occur near the time of onset of an AE event. Cases are discussed where the normal component, defined near the plasma sheet edges, has the opposite sign compared to the normal component defined at the sheet center. For quiet times, the current sheet may be only about 1000 km thick within a 3 earth-radii plasma sheet, and may carry some 10-15% of the total tail current.

Speiser, T. W.↗
NASA NTRS1981

Magnetic pumping of particles in the outer Jovian magnetosphere

The mechanism of magnetic pumping consists of two processes, the adiabatic motion of charged particles in a time-varying magnetic field and their pitch angle diffusion. The result is a systematic increase in the energy of charged particles trapped in mirror (and particularly, magnetospheric) magnetic fields. A numerical model of the mechanism is constructed, compared with analytic theory where possible, and, is used to predict the consequences of the process for cases that are not tractable by analytical means. The model is applied to the outer Jovian magnetosphere for two purposes; to find magnetospheric regions in which the mechanism may energize trapped particles, and to generate distribution functions involving pitch angle diffusion caused by wave-particle interactions. Beyond 20 Jupiter radii in the outer magnetosphere particles may be magnetically pumped to energies of the order of 1-2 MeV and two-temperature distribution functions with 'break points' at 1-4 keV for electrons and 8-35 keV for ions are predicted.

Borovsky, J. E.↗
NASA NTRS1981

The field and plasma configuration of a filament overlying a solar bipolar magnetic region

This paper presents an analytic model for a finite-size straight filament suspended horizontally in a steady state over a bipolar magnetic region. The equations of magnetostatic equilibrium are integrated exactly. The solution obtained illustrates the roles played by the electric current, magnetic field, pressure, and plasma weight in the balance of force everywhere in space. A specific example of a filament of diameter 50,000 km, with a density two orders of magnitude over the corona and supported by a magnetic field of about 4 gauss is included. The filament temperature can take values ranging from a small fraction to a few times the coronal temperature, depending on the internal electric current of the filament. To produce a cool filament, such as the quiescent prominence, the solution is required to have an internal field with a strong component along the filament, giving rise to helical structures. A hot filament such as the X-ray coronal loop can be produced as a twisted magnetic flux tube embedded in a strong background field aligned parallel to the filament and having lower density and temperature. The basic steps of construction can be used to develop models more realistic than the ones presented for their analytic simplicity.

Low, B. C.↗
NASA NTRS1980

Magnetic field satellite /MAGSAT/ spacecraft vector magnetometer calibration

The low-flying MAGSAT spacecraft, launched October 30, 1979, included a Vector Magnetometer to accurately map the magnitude and direction of the magnetic field of the earth. Calibration of the magnetometer included arc-second precision determination of the relative orientations of the three sensor axes in a coordinate system defined by optical references. This determination began with laboratory measurements of the relative alignments of optical components mounted with the magnetometer. The actual calibration procedure then consisted basically of accurate and repeatable positioning of the Vector Magnetometer within a unique magnetic test facility which nulls the earth's magnetic field, then generates magnetic fields of various orientations and strengths. Analysis of the magnetometer sensor outputs together with the position and alignment data then gave the axes orientations. We used precision theodolites and methods related to surveying techniques to achieve the accurate positioning and optical component alignment measurements. The final calibration accuracy exceeded results previously achieved in the facility.

Hinkal, S. W.↗
NASA NTRS1981

Magnetically induced cylindrical stress waves in a thermoelastic conductor

The problem of stress wave generation in a linear thermoelastic solid by a pulsed magnetic field is investigated both analytically and experimentally for a cylindrically symmetric conducting solid. A dynamic response analysis is developed to correlate magnetic, thermal, and stress fields in the solid with the time history of the electric current. In the experiment, a transient magnetic field was applied normal to a large conducting plate with a circular hole. Initially the field was confined to the interior of the circular hole. The field was generated by discharging a large capacitor bank through a solenoidal coil. The plane-stress cylindrical stress waves are 1-D in nature. The relative effects of the magnetic body force and thermoelastic stresses, both generated by the electromagnetic field, are assessed.

Chian, C. T.↗
NASA NTRS1981

New magnetic results from Allende C3/V/

Thermomagnetic analyses of Allende C3(V) suggest that magnetic phases contributing about 15% to saturation magnetization with transition temperatures not greater than 320 C, also contribute about 90% to natural remanence (NRM) and about 80% to the saturation isothermal remanence (SIRM). Phases carrying the dominating part of of the NRM are found to be intergrown, magnetically interacting, and thermally unstable, beginning at temperatures as low as 50 C. The ratio of the NRM/SIRM ranges from 0.004 to 0.006 for the bulk meteorite and from 0.0004 to 0.005 for chondrules of all sizes. The remanent coercive force behavior suggests coexisting magnetic phases with differing Curie points or with the low temperature transitions being due to transformation of a thermally metastable phase.

Wasilewski, P.↗
NASA NTRS1981

The magnetic field of Jupiter - A generalized inverse approach

The estimation of planetary magnetic fields from observations of the magnetic field gathered along a spacecraft flyby trajectory is examined with the aid of generalized inverse techniques, with application to the internal magnetic field of Jupiter. Model non-uniqueness resulting from the limited spatial extent of the observations and noise on the data is explored and quantitative estimates of the model parameter resolution are found. The presence of a substantial magnetic field of external origin due to the currents flowing in the Jovian magnetodisc is found to be an important source of error in estimates of the internal Jovian field, and new models explicitly incorporating these currents are proposed. New internal field models are derived using the vector helium magnetometer observations and the high field fluxgate observations of Pioneer 11, and knowledge of the external current system gained from the Pioneer 10 and Voyagers 1 and 2 encounters.

Connerney, J. E. P.↗
NASA NTRS1982

Magnetic-Gear Concept for Special Applications

Proposed gear has magnetic instead of mechanical teeth. Magnetic gears consists of permanent magnets resembling mechanical gears but with smooth faces and alternating magnetic poles in place of mechanical teeth. Low torque, noncontacting gears useful in special environments.

Chandler, J. A.↗
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 NTRS1981

Observability of atomic line features in strong magnetic fields

The physical properties of atoms in superstrong magnetic fields, characteristic of neutron stars, and the possibility of detecting magnetically strongly shifted atomic lines in the spectra of magnetized X-ray pulsars are discussed. It is suggested that it is recommendable to look for magnetically strongly shifted Fe 26 Lyman lines in rotating neutron stars of not too high luminosity using spectrometers working in the energy range 10 - 20 keV, with sensitivities to minus 4 power photons per sq cm and second, and resolution E/delta E approx. 10-100.

Wunner, G.↗
NASA NTRS1981

ISEE 1 observations of thermal plasma in the vicinity of the plasmasphere during periods of quieting magnetic activity

An investigation of thermal plasma behavior in the vicinity of the plasmasphere during periods of quieting magnetic activity was conducted by combining thermal ion observations made with the plasma composition experiment on ISEE 1 with plasma density profiles obtained from plasma frequency measurements made with the same satellite's plasma wave experiment. During periods in which the magnetic activity quiets, the two regions characterized by H(+):He(+):O(+) (isotropic) and H(+):O(+):He(+) (field-aligned) ion species distributions (in order of dominance) are separated by a new region in which low-energy H(+) and He(+) are found flowing along the magnetic field lines. At other times, following quieting magnetic activity, distributions having peak fluxes at 90 deg pitch angle are observed in this region.

Horwitz, J. L.↗
NASA NTRS1981

Magnetic fields and charged particles around major planets and their satellites

It is noted that whereas Jupiter and Saturn have magnetospheres whose large-scale structure can be understood by analogy with earth, the ways in which the magnetospheres differ are of great interest. At earth, large-scale processes are dominated by convective flows of plasma driven by the solar wind. At Jupiter, centrifugal effects that are driven by planetary rotation are critical. Magnetic particle sources include not only the ionosphere and solar wind (as at earth) but also satellites and rings. The internal planetary magnetic moments controlling the scale of the magnetosphere differ by orders of magnitude between Jupiter and earth. It is pointed out that where the magnetic moments have been modeled from spacecraft data, the restricted spatial sampling has biased the results and limited confidence in details of the models. Voyager data suggest that Io may itself be magnetized and surrounded by an entirely unfamiliar type of magnetosphere.

Kivelson, M. G.↗
NASA NTRS1982

Evidence for solar magnetic loops beyond 1 AU

A description is presented of observations of energetic particles emitted by solar flares into interplanetary magnetic loop-like structures during two different events. In one of these events, the IMP-7 spacecraft detected particles which were injected into an apparently preexisting 'magnetic loop' during the onset of a solar flare particle event. The energetic particles appear to bounce between two magnetic mirrors. During the second event, the spacecraft entered a magnetic field regime where the energetic particle intensities had already reached a characteristic angular distribution indicative of a stably trapped population. Observations of the evolution of the angular distributions of the energetic particle intensities during the solar events reveal the occurrence of unusual particle anisotropies.

Sarris, E. T.↗
NASA NTRS1980

On the search for an intrinsic magnetic field at Venus

Magnetic field observations obtained by the Pioneer Venus orbiter at low altitude are now available for two sets of orbits in the Venus wake. Data from these 130 orbits are examined for possible surface correlated features or any intrinsic magnetic moment. No surface correlated magnetic fields are observed, but the threshold for the detectability of such fields at Venus is about an order of magnitude greater than at the moon. A surface feature of 10 deg extent would have to create an anomaly of at least 5 gammas at 200 km to be detected in the Pioneer Venus data. Using measurements averaged in 72 10 x 10 deg bins, a planetary magnetic dipole moment of 0.87 + or - 3.00 x 10 to the 21st gauss-cu cm is obtained. Thus the upper limit of the present day Venus moment is less than 4 x 10 to the -5th of the terrestrial moment.

Russell, C. T.↗