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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Natural precedents to active magnetospheric experiments

Some of the natural analogs of proposed seeding experiments in the magnetosphere are: electric charged particle injections during substorms; lightning-induced whistlers providing wave injections; 'detachment' of plasma from the plasmapause, which is equivalent to light-ion seeding in the outer magnetosphere. In the present paper, the characteristics of some natural precedents to active experiments are reviewed, and their relative advantages and drawbacks are examined. One of these precedents - wave generation in detached plasma regions - is then discussed in some detail; the discussion reveals the generation of ELF electromagnetic noise when the energetic electrons exceed the stably trapped limit, and also indicates that a critical dimension for the seeded volume exists transverse to the geomagnetic field.

Russell, C. T.↗
NASA NTRS1977

Heavy ion circulation in the earth's magnetosphere

A mechanism for heavy ion circulation in the magnetosphere is proposed. Singly charged ions heavy ions from the plasmasphere are convected intermittently to the dayside magnetopause, accelerated there, swept into the distant tail lobes and boundary layer, and convected earthward in the plasma sheet to reenter the magnetosphere.

Freeman, J. W.↗
NASA NTRS1976

Electrostatic turbulence in the magnetosphere

Plasma wave measurements from the IMP-6, IMP-8 and Hawkeye-1 satellites show that a broad region of intense low-frequency electric field turbulence occurs on the high latitude auroral field lines at altitudes ranging from a few thousand kilometers in the ionosphere to many earth radii in the distant magnetosphere. A qualitatively similar, but less intense, type of electric field turbulence is also observed at the plasmapause during magnetic storms. In the auroral regions the turbulence occurs in an essentially continuous band on the auroral L-shells at all local times around the earth and is most intense during periods of auroral activity. In this paper we summarize the basic characteristics of this electric field turbulence and consider the possible role this turbulence may play in the heating and acceleration of plasma in the magnetosphere.

Gurnett, D. A.↗
NASA NTRS1976

The magnetosphere of Mercury

Data on Mercury's magnetosphere and on the plasma, planetomagnetic, and energetic particle environment of the planet obtained in three encounters (Mariner 10 flybys) are compared, and tasks for future research are outlined. The Mercury bow shock and magnetopause are much closer to the planet than the earth counterparts are to the earth. The magnetotail with embedded plasma sheet-field reversal region, global deflection of the solar wind by an intrinsic dipolar magnetic field, variations in solar wind momentum flux, and absence of such features as ionosphere, plasmasphere, and radiation belts, are described. Energetic electrons are accelerated in the magnetotail, however, and the interplanetary magnetic field variations distort Mercury's magnetosphere to produce a southward field associated with substorm-like disturbances.

Ness, N. F.↗
NASA NTRS1977

Electric and magnetic fields in the high-latitude magnetosphere

The configuration of high-latitude electric and magnetic fields is reviewed. Various results suggest that high-latitude magnetic field lines from the outermost regions of the dayside magnetosphere converge toward a point near the noon meridian. Plasma flows, the midday cusp, and a dawn-dusk electric field across the polar cap are characterized. The electric fields associated with plasma flows produce Hall currents on the polar cap which vary with sector structure. Some evidence indicates that polar cap convection may reverse during intervals of strong northward interplanetary field. It is concluded that most observations are consistent with an open field magnetosphere model.

Fairfield, D. H.↗
NASA NTRS1977

Impulsive penetration of filamentary plasma elements into the magnetospheres of the earth and Jupiter

Assuming that the solar wind plasma is usually nonuniform over distances of 10,000 km or less, it is shown that filamentary plasma elements stretched out from the sun can penetrate impulsively and become engulfed into the magnetosphere. The diamagnetic effects associated with these plasma inhomogeneities are observed in outer magnetospheres and magnetosheaths as dips or directional discontinuities in the magnetic field measurements. From the mean penetration distances of these diamagnetic plasma elements one can deduce a mean deceleration time, as well as an approximate value of the integrated Pedersen conductivity in the polar cusp of the earth and Jupiter.

Lemaire, J.↗
NASA NTRS1977

The magnetospheric boundary layers - A geometrically explicit model

A geometrically explicit three-dimensional model of the magnetosphere is proposed and compared with existing models. The proposed model is a bimodal combination of the classical open and closed magnetosphere. The plasma sheet is topologically contained in a closed field line volume which is exposed to the magnetosheath along the flanks. Boundary layer plasma at the flanks of the closed field line volume freely flows along field lines to the ionosphere and forms a complete border to the plasma sheet. The plasma sheet derives from the closed boundary layer plasma, which is in the same topological volume. The closed boundary layer between the clefts on the dayside is covered by plasma hood (the open field line equatorward extension of the mantle) when dayside merging occurs.

Crooker, N. U.↗
NASA NTRS1977

Nuclear burst plasma injection into the magnetosphere and resulting spacecraft charging

The passage of debris from a high altitude ( 400 km) nuclear burst over the ionospheric plasma is found to be capable of exciting large amplitude whistler waves which can act to structure a collisionless shock. This instability will occur in the loss cone exits of the nuclear debris bubble, and the accelerated ambient ions will freestream along the magnetic field lines into the magnetosphere. Using Starfish-like parameters and accounting for plasma diffusion and thermalization of the propagating plasma mass, it is found that synchronous orbit plasma fluxes of high temperature electrons (near 10 keV) will be significantly greater than those encountered during magnetospheric substorms. These fluxes will last for sufficiently long periods of time so as to charge immersed bodies to high potentials and arc discharges to take place.

Pavel, A. L.↗
NASA NTRS1977

Study of effects of space power satellites on life support functions of the earth's magnetosphere

The effects of the Satellite Solar Power System (SSPS) on the life support functions of the earth's magnetosphere were investigated. Topics considered include: (1) thruster effluent effects on the magnetosphere; (2) biological consequences of SSPS reflected light; (3) impact on earth bound astronomy; (4) catastrophic failure and debris; (5) satellite induced processes; and (6) microwave power transmission. Several impacts are identified and recommendations for further studies are provided.

Douglas, M.↗
NASA NTRS1978

The transfer of cyclotron lines through the magnetospheric shell of Hercules X-1

Cyclotron emission from a strong magnetic field, has been proposed to identify line feature observed in the hard X-ray spectrum of the neutron star Hercules X-1. If this interpretation is indeed correct, and if the model wherein the 1.24 second hard X-ray pulse is due to the occultation of a more isotropic X-ray flux by an opaque magnetospheric shell is accepted then these observations can be used to place strict limits on the total source luminosity of the cyclotron emission. The observational fate of cyclotron line photons that have emerged from the region near the neutron star surface, but have yet to encounter an opaque shell at the magnetosphere is discussed. It is shown that if a narrow line is incident on such a shell, then a residual narrow feature can emerge from the shell.

Weave, R. P.↗
NASA NTRS1978

Particle acceleration in pulsar magnetospheres

The structure of pulsar magnetospheres and the acceleration mechanism for charged particles in the magnetosphere was studied using a pulsar model which required large acceleration of the particles near the surface of the star. A theorem was developed which showed that particle acceleration cannot be expected when the angle between the magnetic field lines and the rotation axis is constant (e.g. radial field lines). If this angle is not constant, however, acceleration must occur. The more realistic model of an axisymmetric neutron star with a strong dipole magnetic field aligned with the rotation axis was investigated. In this case, acceleration occurred at large distances from the surface of the star. The magnitude of the current can be determined using the model presented. In the case of nonaxisymmetric systems, the acceleration is expected to occur nearer to the surface of the star.

Baker, K. B.↗
NASA NTRS1977

Interplanetary magnetic field and magnetospheric substorms

The interplanetary magnetic field (IMF) changes and the associated responses of the magnetosphere on November 1, 1972, are examined. IMF Bz changes consisted of a sudden southward turning, a slow northward turning, and a subsequent steady northward sense. Magnetospheric substorms occurred throughout this period.

Akasofu, S.-I.↗
NASA NTRS1977

Observations of large transient magnetospheric electric fields

Transient electric field events were studied by means of the long double-probe instrumentation carried by the Imp 6 satellite, and nine clearly defined exceptionally large amplitude events are described. The events were observed in the midnight sector at geocentric distances of 3.5 to 5.5 earth radii at middle latitudes within a magnetic L shell range of 4.8 to 7.5; the duration is from one to several minutes with peak power spectra amplitudes occurring at a frequency of about 0.3 Hz. The events occur under magnetically disturbed conditions and are often associated with negative dH/dt excursions. The magnetospheric motions calculated for these electric fields indicate a quasi-stochastical diffusive process rather than the general inward magnetospheric collapsing motion expected during the expansive phases of auroral substorm activity. It is likely that the transient electric fields are responsible for the impulsive acceleration and injection of plasma to populate the outer radiation belt.

Aggson, T. L.↗
NASA NTRS1978

Magnetospheric substorms

The generation of magnetospheric substorms as a magnetospheric response to a rectangular wave of a component of the interplanetary magnetic field is discussed. The development and decay of auroral substorms (the only visible manifestations of magnetic substorms) are described with reference to auroral particle precipitation, joule heat dissipation, and ring current injection. Various models of substorm phenomena are reviewed, including: (1) the conversion of magnetotail magnetic energy, (2) hot plasma injection from the plasma sheet into the Van Allen belt and ring current formation, (3) field-aligned currents and the auroral electrojet, and (4) the nature of interplanetary magnetic field fluctuations.

Akasofu, S.-I.↗
NASA NTRS1978

Acceleration of protons at 32 Jovian radii in the outer magnetosphere of Jupiter

A rapid ten-fold increase of proton flux was observed at 32 Jovian radii in Jupiter's outer magnetosphere. The total event lasted about 30 minutes and was composed of many individual events. Both before and after the event, proton flux was similar to the low-flux level found between crossings of the magnetic equator. Measurements of angular distributions and the time histories of proton and alpha particle channels at different energies indicate that the flux increase is caused by local acceleration. It is suggested that the average particle population in the outer magnetosphere is caused by a state of dynamic equilibrium between acceleration and loss processes.

Schardt, A. W.↗
NASA NTRS1978

Possible origins of time variability in Jupiter's outer magnetosphere. III - Variations in the heavy ion plasma

The implications of a heavy ion plasma in the Jovian magnetosphere are discussed. The plasma electron density varies on time scales comparable with that of radial diffusion. This plasma can enhance a super-Alfvenic planetary wind by increasing the radial mass flux. A mechanism by which the heavy ion plasma can regenerate itself via self-sputtering from the surface of Io followed by ionization first by solar ultra-violet and later by electron impact is proposed. It is suggested that this long term variability can modulate the faster variations of the plasma-magnetosphere configuration of Jupiter.

Eviatar, A.↗
NASA NTRS1978

Correction to 'Recirculation of energetic particles in Jupiter's magnetosphere'

An error in Pioneer 11 data reduction software has, when present, caused a phase shift of 180 deg in the assignment of spacecraft roll angles. The corrected analysis of the pitch angle distributions of energetic particles in Jupiter's magnetosphere reveals significant proton anisotropies directed toward the planet in the southern hemisphere, contrary to the authors' (1975) original report. In the northern hemisphere, both proton and electron anisotropies are directed away from the planet, as reported previously. The revised data show that the claim of direct evidence for the hypothesis of recirculation of energetic particles in the Jovian magnetosphere is invalid. It is suggested that indirect evidence still supports the hypothesis, although the recirculation process must be weaker than originally envisioned and obscured by other processes.

Sentman, D. D.↗
NASA NTRS1978

Simultaneous multispacecraft observations of energetic proton bursts inside and outside the magnetosphere

Energetic proton bursts were observed simultaneously on Imp 6, 7, and 8 both inside and outside the earth's magnetosphere during the period October 1972 through August 1974. It is found that proton bursts are present nearly simultaneously in the vicinity of the outer belt trapping boundary, in the low-latitude magnetotail, in the magnetosheath, and upstream from the bow shock. Large intensity differences, time delays, and differences in energy spectra recorded by the three spacecraft are described. It is suggested that energetic protons and electrons are probably accelerated inside the plasma sheet and propagate to various regions both inside and outside the magnetosphere.

Sarris, E. T.↗