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At least 1,621 records · Page 90
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NASA NTRS1982

The use of artificial electron beams as probes of the distant magnetosphere

The use of artificial electron beams as probes of the distant magnetosphere is discussed. The accelerators, the method of injecting and analyzing the beams using television techniques and particle counters, and how the beams simulate the natural trapped electrons are summarized. It is found that when an electron beam is injected from a sounding rocket in the ionosphere, the rocket potential rises to a positive value and collects a current of ionospheric plasma electrons. It is proposed to use optical methods on the Space Shuttle to analyze electron beams injected in orbit, and in view of the results of the ECHO 5 experiments, such optical techniques may prove ineffective due to background luminosity from the ground and other sensitivity limitations.

Winckler, J. R.↗
NASA NTRS1982

Chorus-related electrostatic bursts in the earth's outer magnetosphere

Studies of wideband plasma wave data from the ISEE 1 and ISEE 2 spacecraft are reported which reveal that whistler-mode chorus emissions in the earth's outer magnetosphere are often accompanied by high-frequency bursts of electrostatic noise. The chorus features that correlate to the electrostatic bursts have a hook-like frequency-time variation in the frequency range 200-400 Hz, and the associated electrostatic bursts have a frequency range of about 4-8 kHz. In some cases these electrostatic bursts have a harmonic frequency structure with a frequency spacing corresponding to the chorus frequency. This harmonic structure apparently results from the fact that the burst intensity is modulated at the chorus frequency.

Reinleitner, L. A.↗
NASA NTRS1982

The induced magnetosphere of Titan

No evidence was found for an intrinsic magnetic field, nor for the development of a bow shock wave, as the corotating Saturnian magnetoplasma convected past Titan during the Voyager 1 close encounter of November 12, 1980. The observation of a well-developed, induced bipolar magnetic tail is evidence, however, of a strong electrodynamic interaction. Three thin, current-carrying regions were crossed which correspond to the inbound and outbound tail magnetopause and an imbedded tail neutral sheet. The interaction is unique among those observed to date in the solar system, in that it is intermediate with respect to sonic and Alfvenic Mach numbers by comparison with Titan in the solar wind and Io in the Jovian magnetosphere. The draping of the Saturnian magnetic field around the ionosphere of Titan is suggested by results of the analysis of magnetic field data.

Ness, N. F.↗
NASA NTRS1982

Effects of Titan on trapped particles in Saturn's magnetosphere

Magnetic field data from Voyager 1 magnetometer experiment are used with angular distribution data from the same spacecraft's low energy charged particle experiment to investigate the influences of Titan on the magnetosphere energetic particle distributions, with attention to the pitch angle distributions of ions and electrons. Titan appears to disrupt the corotation motion of the ions, since, while the fluxes of the ions in the corotation direction are of diminished intensity, those observed in the equatorial plane perpendicular to this direction are almost unaffected. The resulting distribution and trajectory modeling conclusions suggest that the convection electric field is absent in the wake of Titan, and that the presence of Titan produces a reduction in the fluxes of the electrons and flatter distributions with pitch angle.

Maclennan, C. G.↗
NASA NTRS1982

Turbulent electric fields in the nightside magnetosphere

Electric field measurements from the long-wire double-probe instrument (baseline of 179 m) on ISEE 1 have shown the magnetospheric electric field on auroral L shells to be extremely turbulent during periods of magnetic activity. During intense activity these turbulent electric fields can penetrate to very low L values. The variational component of the electric field is typically larger than the DC value. Measurements are presented at frequencies up to 14 Hz. Magnitudes of over 40 m V/m (zero to peak) have been observed with spectral power levels in the 1-10 Hz range greater than m squareV/sq m Hz. The spectral shape of the most intense events was generally flatter than that predicted by two-dimensional hydromagnetic cascading of energy, which argues that the source of this turbulence must be driving the plasma near these frequencies. This in turn suggests that the instability is in the low-energy plasma.

Maynard, N. C.↗
NASA NTRS1982

Light ion concentrations in Jupiter's inner magnetosphere

The light ion distribution in the inner Jovian magnetosphere is investigated using whistler dispersion measurements from the Voyager 1 plasma wave instrument and heavy ion plasma concentrations from the plasma instrument. Two models are developed for the light ion concentration over 14 L shells between L = 5.2 and 6.2, one giving a constant concentration along the field line and the other corresponding to an exponential density distribution. Due to heavy ion concentrations near the equator that are typically an order of magnitude larger than the light ion concentration, results obtained are mainly relevant to the light ion concentration outside of the torus. Light ion concentration near the equator ranges from about 1-10% of the heavy ion concentration, while outside the torus the light ions are the dominant species.

Tokar, R. L.↗
NASA NTRS1982

The hidden ion population of the magnetosphere

The presence of a cold ion population in the magnetosphere which is normally hidden from particle detector observation by the positive charging of the spacecraft is reported. Ion and electron data were obtained from particle detectors on the ATS 6 and SCATHA satellites designed to measure the 1-eV to 80-keV plasma population. The cold, isotropic ion population, with temperature 1 eV and density 10-100/cu cm, was detected only when the spacecraft were in eclipse, when spacecraft potential had dropped from +10 V in sunlight to +4 to +5 V. The hidden ion population was found at geosynchronous altitude only during geomagnetically quiet times and when there has been an absence of geomagnetic activity for several hours, and appears to coexist with the plasma sheet. More consistent measurements of the cold ion population at midnight or at other local times would require the biasing of the ion detector with respect to the spacecraft, or the controlling of spacecraft potential.

Olsen, R. C.↗
NASA NTRS1982

Highlights of theoretical progress related to the International Magnetospheric Study

U.S. theoretical research efforts have addressed three areas within the International Magnetospheric Study. The first, solar wind/magnetosphere interaction, is presently concerned with the suggestion that magnetic merging may predominantly occur near the polar cusps rather than near the subsolar point. Mechanisms have been proposed for noncollisional diffusion of solar wind plasma across the closed magnetopause entailed by such a phenomenon. The second area considers the importance to magnetotail dynamics of a continuous source of solar wind plasma, and of sporadic plasma loss associated with an unsteady convection cycle. In the third area, the electrodynamic magnetosphere/ionosphere interaction, an advanced state has been reached in the understanding of the relevant physics, with respect both to coupling in the subauroral region and the large scale structure of auroral zone electric fields parallel, and perpendicular to, the magnetic field.

Hill, T. W.↗
NASA NTRS1982

A comparison of the 0.1-17 keV/e ion composition in the near equatorial magnetosphere between quiet and disturbed conditions

Data from the near-equatorial magnetosphere are analyzed by comparing the plasma composition during storm conditions with the composition during extended periods of low magnetic activity. It is found that at L less than or equal to 5, the O(+) is typically comparable to the H(+) in density and is often the dominant species, particularly during quiet times and at the inner edge of the region of significant fluxes. The He(+) in most cases contributes a significant fraction of the density and is sometimes the second most abundant species, following the O(+). Another finding is that both the He(+)/H(+) and the O(+)/H(+) ratios peak at the lowest L values and are, on the average, higher during quiet times than they are during the early main phase of major magnetic storms; this is seen as suggesting that charge exchange may be a significant loss process at low L. It is pointed out that the mean energies of the H(+), He(+), and O(+) ions often decrease gradually with decreasing L toward the inner edge of the energetic particle population.

Lennartsson, W.↗
NASA NTRS1982

The discovery of nitrogen ions in the earth's magnetosphere

Operating in a mass scanning mode, the Retarding Ion Mass Spectrometer (RIMS) has measured N(+) and N(++) ions in the magnetosphere. Both N(+) and N(++) are observed in the plasmasphere, with N(+) ions also seen flowing out of the northern polar cap at altitudes up to 3 earth radii. The N(+) fluxes are 5 to 10% of the O(+) fluxes with the N(++) fluxes at 1-5% of the N(+) fluxes.

Chappell, C. R.↗
NASA NTRS1982

Interaction between the SPS solar power satellite solar array and the magnetospheric plasma

The results of study to determine the effects of space plasmas on a large GaAs solar cell array using solar reflectors at a concentration ratio of two in geostationary orbit are summarized. It was concluded that the system could function in the GEO environment if certain design changes were implemented. These included conductive coatings on the solar cells, changing the reflector material from Kapton to a higher conductivity material, and oversizing the array to compensate for a 0.7% parasitic load due to losses from the ambient magnetospheric plasma. The operation of the solar powered earth orbit transfer vehicle (EOTV) was also examined and it was concluded that LEO servere arcing would take place on all high voltage negative portions of the array. The parasitic load loss at LEO was estimated at 3%. Operation of a high voltage array at LEO represents a major problem. Charge exchange ion feedback from argon ion thrusters located near the EOTV solar array was also examined and all problems found were believed to be solvable by the placement of protective ground screens.

Freeman, J. W.↗
NASA NTRS1982

Magnetospheric ray tracing studies

Using a model of Jupiter's magnetized plasma environment, radiation raypaths were calculated with a three-dimension ray tracing program. It is assumed that energetic particles produce the emission in the planet's auroral zone at frequencies just above the electron gyrofrequencies. This radiation is generated in narrow sheets defined by the angle of a ray with respect to the magnetic field line. By specifying the source position: latitude, longitude, and radial distance from the planet, signatures in the spectrum of frequency versus time seen by Voyager 1 and 2 were duplicated. The frequency range and the curvature of the decametric arcs in these dynamic spectra are the result of the geometry of the radiation sheets (imposed by the plasma and by the B-field) and illumination of Voyager 1 and 2 as the rotating magnetosphere mimics a pulsar.

Six, N. F.↗
NASA NTRS1982

The flux and source of energetic protons in Saturn's inner magnetosphere

The flux of energetic protons in Saturn's inner magnetosphere was observed in two channels from 48 to 63 and 63 to 160 MeV. Absorption features due to the G ring and the satellites Enceladus and Mimas were easily identifiable. The flux observed in the absorption slot of Mimas can be maintained by the decay of a cosmic ray albedo neutron flux of 0.007/sq cm/s/sr. This flux is entirely consistent with calculations of the neutron flux produced by galactic cosmic ray interactions with the rings of Saturn. The omnidirectional proton flux of 0.0082/sq cm/s at 2.734 R sub s requires a residence time of 30 years. Both the residence time and the energy spectrum are comparable to those found in the inner radiation belt of the Earth. The angular distribution is nearly isotropic in the Mimas slot and beyond 4R sub s. Otherwise the pitch angle distribution is pancake and is approximated by sin(n)theta with n in the range 2 to 7. This distribution is consistent with an isotropic neutron source in the ring plane.

Schardt, A. W.↗
NASA NTRS1982

Three dimensional ray tracing Jovian magnetosphere in the low frequency range

Ray tracing of the Jovian magnetosphere in the low frequency range (1+40 MHz) has resulted in a new understanding of the source mechanism for Io dependent decametric radiation (DAM). Our three dimensional ray tracing computer code has provided model DAM arcs at 10 deg. intervals of Io longitude source positions for the full 360 deg of Jovian system III longitude. In addition, particularly interesting arcs were singled out for detailed study and modelling. Dependent decametric radiation arcs are categorized according to curvature--the higher curvature arcs are apparently due to wave stimulation at a nonconstant wave normal angle, psi. The psi(f) relationship has a signature that is common to most of the higher curvature arcs. The low curvature arcs, on the other hand, are adequately modelled with a constant wave normal angle of close to 90 deg. These results imply that for higher curvature arcs observed for from Jupiter (to diminish spacecraft motion effects) the electrons providing the gyroemission are relativistically beamed.

Menietti, J. D.↗
NASA NTRS1983

Currents in Saturn's magnetosphere

A model of Saturn's magnetospheric magnetic field is obtained from the Voyager 1 and 2 observations. A representation consisting of the Z sub 3 zonal harmonic model of Saturn's planetary magnetic field together with an explicit model of Saturn's planetary magnetic field and a model of the equatorial ring current fits the observations well within r 20 R sub S, with the exception of data obtained during the Voyager 2 inbound pass.

Connerney, J. E. P.↗
NASA NTRS1983

Fast magnetospheric echoes of artificially injected electrons observed above a bright auroral arc

Rocket-borne electron beam experiments confirmed earlier observations of fast magnetospheric echoes of artificially injected energetic electrons. A total of 234 echoes were observed at pitch angles from 9 to 10 deg at energies of 1.87 and 3.90 keV. Of these, 102 echoes are unambiguously related to preceding accelerator operations at 2, 4 or 8 keV energy and highest current levels resulting in the determination of transit times of typically 300 to 400 msec. When echoes are present in both energy channels, higher energy electrons lead lower energy ones by 50 to 70 msec. Adiabatic theory applied to the observations yields a reflection height of 3000 to 4000 km.

Wilhelm, K.↗
NASA NTRS1982

Modelling of auroral electrodynamical processes: Magnetosphere to mesosphere

Research conducted on auroral electrodynamic coupling between the magnetosphere and ionosphere-atmosphere in support of the development of a global scale kinetic plasma theory is reviewed. Topics covered include electric potential structure in the evening sector; morning and dayside auroras; auroral plasma formation; electrodynamic coupling with the thermosphere; and auroral electron interaction with the atmosphere.

Chiu, Y. T.↗
NASA NTRS1982

Solutions to the equations for corotating magnetospheric convection

The equations of centrifugally driven convection appropriate to a treatment of the transport of Io plasma in Jupiter's magnetosphere are solved for two special cases of the source distribution. The results show that, in the corotating frame of Jupiter, the mass flows outward from the source, forming spirallike streamlines. It is found that the pitch of a spiral depends on the amount of resident mass and the ionospheric conductivity and that the outflow speed depends on the size of the source region, the resident mass, and the source strength of new ions. An example of a wide source and slow outflow is presented. It is noted that, in the limit of a narrow source, the outflow is rapid and the streamlines are nearly radial.

Summers, D.↗