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NASA NTRS1986

The magnetosphere of Uranus

The magnetosphere and magnetic field of Uranus are analyzed using Voyager 2 data. It is observed that the magnetic axis of Uranus is tilted 60 deg from its rotation axis; the magnetic dipole center is displaced almost 7700 km from the center of the planet; the magnetic field intensity varies over its surface between 24,000-69,000 gammas; and the rotation rate of the planet is 17.24 hours. The dynamo generation of the planetary magnetic field is examined. Consideration is given to the auroral activity, magnetic tails, moons, and radiation belts of charged particles of Uranus. The significance of the large tilt and offset magnetic axis for the interior of Uranus is discussed.

Ness, Norman F.↗

NASA NTRS1987

The solar wind-magnetosphere-ionosphere current-voltage relationship

The global current-voltage relationship for the solar wind-magnetosphere-ionosphere system (SW-M-I) is investigated, restricting the study to strong southward IMF. The dynamo presently identified is on open field lines, and it operates at close to short circuit and at a fraction of the available power output. Control of the dynamo by ionospheric conductivity is discussed. Implications of the simulation results, including the relationship between open and closed field dynamos, the effect of solar wind conditions, the control of reconnection on the bow, the size of the open field line region, and the effects of increased auroral conductivity, are discussed.

Fedder, J. A.↗

NASA NTRS1987

Nonlinear, relativistic Langmuir waves in astrophysical magnetospheres

Large amplitude, electrostatic plasma waves are relevant to physical processes occurring in the astrophysical magnetospheres wherein charged particles are accelerated to relativistic energies by strong waves emitted by pulsars, quasars, or radio galaxies. The nonlinear, relativistic theory of traveling Langmuir waves in a cold plasma is reviewed. The cases of streaming electron plasma, electronic plasma, and two-streams are discussed.

Chian, Abraham C.-L.↗

NASA NTRS1987

Microphysics of the auroral acceleration region of other regions of the magnetosphere

Electric field and plasma measurements pertinent to the microphysics of the auroral acceleration region are reviewed. Observations in other regions of the magnetosphere, which appear to involve similar physical processes, are summarized in order to emphasize the requirement on Cluster instrumentation for wide dynamic range, high time resolution, time domain field, and particle measurements. It is suggested that the microphysics of current driven instabilities in the auroral acceleration region is duplicated in the high latitude boundary of the plasma sheet and that the macroscale structure of the tail is determined by this microphysics.

Mozer, F. S.↗

NASA NTRS1987

Highly relativistic magnetospheric electrons - A role in coupling to the middle atmosphere?

Twenty-seven-day periodic enhancements of the relativistic electrons are observed in association with concurrently measured solar wind streams, and a numerical transport code is used to investigate the coupling of these high-energy electrons to earth's upper and middle atmosphere. When precipitated, these electrons are found to show a large energy deposition at 40-60 km altitude which is 3-4 orders of magnitude greater than the galactic cosmic ray or solar EUV energy deposition at these altitudes. It is suggested that this electron population could play a role in coupling solar wind and magnetospheric variability to the middle atmosphere through a modulating effect on lower D-region ionization and possibly on upper level ozone chemistry.

Baker, D. N.↗

NASA NTRS1987

Pitch angle distributions of low-energy ions in the near-earth magnetosphere

Energetic ion composition data acquired by satellite have been used to study the characteristics of ion pitch angle distributions in the near-earth magnetosphere. Both H(+) and O(+) ions below 1 keV were most frequently observed to have bidirectional field-aligned or conical pitch angle distributions inside L of about 6, with the exception of highly trapped H(+) very near the magnetic equator. The occurrence probability distributions of counterstreaming ions (CSI) and bidirectional conics in magnetic local time and L shell space suggest that the observed CSI were formed near the postmidnight sector and subsequently drifted eastward, and that ions close to the field-aligned direction were probably lost due to charge exchange with atmospheric hydrogen in the course of their eastward drift. In the prenoon sector, conical distributions dominated. Bidirectional ions were vary rarely observed in the afternoon sector, presumably because their drift paths crossed the magnetopause into the dayside magnetosheath.

Sagawa, E.↗

NASA NTRS1987

Magnetosphere, ionosphere and thermosphere; Proceedings of the Topical Meeting of the Twenty-sixth COSPAR Plenary Meeting, Toulouse, France, June 30-July 11, 1986

Papers are presented on satellite observations of new particle and field signatures associated with SAR arc field lines at magnetospheric heights, the structure of the polar oval from simultaneous observations of the optical emissions and particle precipitations during the period of high solar activity between 1981 and 1982, and SAR-arcs and emissions in the main trough of the electron concentration. Also considered are a model calculation of hydrogen Balmer emissions under various modes of proton precipitation, electron precipitation near L = 4, and an investigation of the thermosphere-ionosphere interaction by means of the neutral post-storm effect. Other topics include auroral electric field penetration into the middle-latitude trough, field-aligned currents and related phenomena in the cust, and the positive phase of ionospheric storms and its connection with the dayside cusp.

Schmerling, E. R.↗

NASA NTRS1987

Electrostatic waves in the magnetosphere of Uranus

Observations of electrostatic waves in the magnetosphere of Uranus are discussed with attention focused on the Bernstein emissions. The most intense Bernstein waves were observed near the magnetic equator of the planet, even though the tilt of the Uranian magnetic moment is very large relative to the rotational axis. In addition to the Bernstein modes, a number of highly sporadic emissions were detected in the vicinity of the Miranda L shell.

Kurth, W. S↗

NASA NTRS1987

Energetic ion and electron phase space densities in the magnetosphere of Uranus

Proton and electron phase space density profiles are constructed from an analysis of Voyager 2 low-energy charged particle data from the magnetosphere of Uranus. The Uranus proton profiles reveal an approximately exponential decline with decreasing radius for L less than about 9 in a relatively dense thermal plasma region with intense plasma wave activity. Among the distributed loss mechanisms at Uranus are satellite sweeping, wave-particle interactions, and charge exchange of protons with an extended hydrogen corona.

Cheng, Andrew F.↗

NASA NTRS1988

Prediction of radio frequency power generation of Neptune's magnetosphere from generalized radiometric Bode's law

Magnetospheric radio frequency emission power has been shown to vary as a function of both solar wind and planetary values such as magnetic field by Kaiser and Desch (1984). Planetary magnetic fields have been shown to scale with planetary variables such as density and angular momentum by numerous researchers. This paper combines two magnetic scaling laws with the radiometric law to yield 'Bode's'-type laws governing planetary radio emissions. Further analysis allows the reduction of variables to planetary mass and orbital distance. These generalized laws are then used to predict the power otuput of Neptune to be about 1.6 x 10 to the 7th W; with the intensity peaking at about 3 MHz.

Million, M. A.↗

NASA NTRS1988

A study of field-aligned currents observed at high and low altitudes in the nightside magnetosphere

Field-aligned current structures on auroral field lines observed at low and high altitudes using DE 1 and ISEE 2 magnetometer, and particle data observed when the spacecraft are in magnetic conjunction in the near-midnight magnetosphere, are investigated. To minimize latitudinal ambiguity, the plasma-sheet boundary layer observed with ISEE 2 and the discrete aurora at the poleward edge of the auroral oval with DE 1 are studied. The overall current observed at highest latitudes is flowing into the ionosphere, and is likely to be carried by ionospheric electrons flowing upward. There are, however, smaller-scale current structures within this region. The sense and magnitude of the field-aligned currents agree at the two sites. The ISEE 2 data suggests that the high-latitude downward current corresponds to the high-latitude boundary of the plasma-sheet boundary layer, and may be associated with the ion beams observed there.

Elphic, R. C.↗

NASA NTRS1988

Particle acceleration in accreting magnetospheres

The possibility that energetic protons are accelerated within the closed magnetosphere of accelerating neutron stars is considered. The accelerating mechanism is suggested to be plasma turbulence excited by the accretion flow. Rough estimates show that this mechanism may be capable of accelerating protons to the energies of about 10 to the 16th eV required to explain observations of about 10 to the 15th eV gamma rays from some thermal X-ray sources. Proton synchrotron radiation may be observable at energies ranging from the infrared to about GeV gamma rays.

Katz, J. I.↗

NASA NTRS1988

Eigenfunctions of the magnetospheric radial-diffusion operator

The applicability of eigenfunction methods to the theory of magnetospheric radial diffusion is investigated analytically, with a focus on the operator (Lambda) for radiation-belt and ring-current particles. It is shown that the eigenfunctions of Lambda can be expressed in terms of a linear combination of ordinary Bessel functions of the first and second kinds, and that the solution for the drift-averaged phase-space density can be expressed as the sum of a quasi-static solution and a time-dependent superposition of the eigenfunctions of Lambda. Results for illustrative and practical sample problems are presented in extensive tables and graphs and discussed in detail.

Schulz, Michael↗

NASA NTRS1988

Corotation lag of Saturn's magnetosphere - Global ionospheric conductivities revisited

In view of the recent publication of Eviatar and Richardson (1986), who have calculated the Pedersen conductance of Saturn's ionosphere to be much smaller than previous estimates, the Pedersen conductance is recalculated using the same neutral atmosphere model as these authors. The results confirm the earlier estimates that the ionospheric Pedersen conductance of Saturn's ionosphere ranges from 0.3 to 17 mho near the terminator as a function of latitude. The source of discrepancy appears to be the inclusion by Eviatar and Richardson of ion density into the ion-neutral collision frequency term, which is incorrect. Contrary to the conclusion of Eviatar and Richardson, Saturn's ionospheric Pedersen conductance is high enough to impose nearly perfect corotation between the ionosphere and the magnetosphere.

Cheng, Andrew F.↗

NASA NTRS1987

The auroral kilometric radiation from Uranus and its magnetospheric implications

The Gulkis and Carr (1987) emission beam model for the kilometric radio emission from Uranus and types of information regarding the Uranian inner magnetosphere that may be derivable from its application are discussed. A modeled electron density profile is presented. The manner in which the hollow-cone beam from each element of the distributed auroral-zone source varies with frequency is determined. It is suggested that the observed effects might be due to refraction by a smooth component of the electron density variation with distance, together with multiple small refractions by electron density inhomogeneities along the ray path.

Carr, Thomas D.↗

NASA NTRS1988

Dual periodicity of the Jovian magnetosphere

Using data from the 1979 Voyager flybys of Jupiter and two sets of ground-based observations of the Io torus, this paper presents an extensive analysis concerning the nature of the second magnetospheric periodicity of the Jupiter's magnetic field, along with a definition of a new Jovian matching coordinate system (referred to as system IV). It is shown that available independent data sets covering a time interval of 4 years, which either drift or show no particular organization in system III, fit mutually consistent patterns in system IV. Provisional values are derived for a transformation between systems III and IV. It is emphasized that system IV needs to be tested against additional data before its durability is assured.

Sandel, B. R.↗

NASA NTRS1988

Asessment of the boundary layer model of the magnetospheric substorm

Data on energetic protons, thermal electrons, and magnetic field characteristics obtained by the ISEE 3 in the magnetotail at the distance of 80 R(E) from the earth were analyzed. Many features were found that were present in the ISEE 1 and 2 data. In particular, flow directions of the plasma observed at 80 R(E) were found to be quite consistent with the formation of the near-earth neutral line during the expansion phase, giving further support to the near-earth reconnection model of the magnetospheric substorm described by Eastman et al. (1985).

Nishida, A.↗

NASA NTRS1988

Observational and theoretical evidence for anisotropies in Saturn's magnetosphere

A study of plasma anisotropies in Saturn's magnetosphere was conducted using data from the Voyager 1 plasma science (PLS) instrument together with an improved Voyager plasma data analysis routine of Sands (1987) and Sands and McNutt (1988). First, the degree of anisotropy required to reconcile differences in the inbound and outbound Voyager 1 plasma observations was determined. The anisotropies derived from the PLS plasma data were then compared with those required to reconcile inbound-outbound differences in plasma flux shell content. It was found that better fits to the data could be obtained if temperature anisotropies were allowed and that the magnitude of the anisotropies was roughly consistent with those required to provide azimuthal symmetry in the plasma flux tube content.

Richardson, John D.↗