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Maclennan, C. G.

Publications and source records attributed to Maclennan, C. G..

29 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Low-energy particles at the bow shock, magnetopause, and outer magnetosphere of Saturn

The characteristics of the dayside bow shock, magnetopause, and outer magnetosphere are emphasized in the present consideration of low energy electrons and protons measured by the Low Energy Charged Particle Experiment during Voyager spacecraft encounters with Saturn. During several of the bow shock crossings, low energy protons were observed streaming from the magnetosphere's dawnside, and in the magnetosheath, the protons were observed to be primarily oriented with pitch angles of about 90 deg. Examination of proton flux distributions suggests that the magnetopause was moving inward with a lower limit speed of 10 km/sec during the Voyager 2 approach to the planet. Intervals of diamagnetic depression observed in the magnetic field energy density during the Voyager 2 encounter nearly coincide with enhancements in the low energy-proton energy density.

Maclennan, C. G.↗
NASA NTRS1983

Energetic ion losses near Io's orbit

The interactions between Io and the Jovian particle population have been of considerable interest ever since the discovery that Io modulates Jupiter's decametric radiation. Voyager 1 observations established that a plasma torus around Io dominates the mass and energy budgets of the Jovian magnetosphere. This torus must then play a central role in the particle loss process around Io. The present investigation provides a picture for particle transport and energetic ion losses near Io's orbit which considers both low energy plasma data and energetic ion data. The approximate match between the energy needed to power the Jovian UV aurora and the 'missing' energy of the low energy charged particle (LECP) measured ions is consistent with the concept that significant precipitation of energetic ions into the Jovian atmosphere can maintain the Jovian aurora.

Cheng, A. 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 NTRS1981

Ion and electron angular distributions in the Io torus region of the Jovian magnetosphere

Angular distributions are presented of ion (about 0.5-2 MeV) and electron (greater than 10 MeV) fluxes measured during the Voyager 1 spacecraft passage through the inner regions of the Jovian magnetosphere. In the regions of peak flux intensities, just outside the orbit of Io, the ion angular distributions are most sharply peaked at 90 deg local pitch angle, a configuration consistent with diffusion of the particles inward from large radial distances. Inside the orbit of Io the lower-energy ions exhibit angular distributions depleted at 90 deg local pitch angles, suggesting the possibility of charge-exchange scattering loss of these particles. In the vicinity of the Io flux tube, no significant effect is observed in the flux or pitch angle distributions of the ions. The relativistic electrons are depleted in the flux tube region and exhibit an asymmetrical pitch angle distribution, with more electrons appearing to arrive from the equatorial region (the direction of Io) than from the low-altitude mirror point.

Lanzerotti, L. J.↗
NASA NTRS1981

Low-power portable geophysical data acquisition system and its use in geomagnetic measurements

A low-power portable data acquisition system presently in use for geomagnetic measurements is described. The system is composed of a data-processing system containing a low-power microprocessor, a 9-track digital tape recorder, and a rechargeable battery pack. The magnetometer is a low-power three axis fluxgate design. Under program control the data processing system keeps track of time of day and date, samples three analog magnetometer outputs at intervals of either 0.4 or 2 s, digitizes the data to 15-bit resolution, and, depending upon relative magnetic activity, decides upon data compression to increase the tape storage capacity. It also monitors and records internal voltages and provides self-checking functions which may be monitored through a visual readout on the control panel. The system is mounted in a rugged, weather-tight carrying case suitable for use outdoors with minimal protection. The system, including magnetometer, uses 1.6-W power and can store 5.7 Mbytes of data.

Medford, L. V.↗
NASA NTRS1981

Polarization characteristics of hydromagnetic waves at low geomagnetic latitudes

A field campaign, using three magnetometer stations spaced in latitude around the equatorial magnetic field distance L approximately 1.9, was conducted in early 1979 to investigate the polarization characteristics of hydromagnetic waves at low geomagnetic latitudes. The magnetic pulsations are observed to have periods in the range approximately 20-25 s and to occur primarily in the local morning hours. Statistically, the polarizations at all three stations were predominantly left handed in the local morning hours and right handed in the local afternoon. At the highest-latitude station (L approximately 2) the orientation of the major axis of the polarization ellipse changed from a predominantly NW-SE direction in the local morning to a mixed NW-SE/NE-SW direction in the afternoon. These two statistical results are consistent with the excitation of the waves by the Kelvin-Helmholtz instability at the magnetopause. However, frequent changes in phase are often observed in the magnetic variations, which result in polarization variations on the time scale of minutes, a situation not readily reconcilable with the Kelvin-Helmholtz instability. The existence of the waves at very low latitudes, furthermore, places constraints on the damping rate of externally excited surface waves inside the magnetosphere. We conclude that present theories for hydromagnetic waves in the geomagnetosphere cannot readily incorporate all of these low-latitude results.

Lanzerotti, L. J.↗
NASA NTRS1980

Intensity variations in plasma flow at the dawn magnetopause

Observations of plasma flows in the region of the dawn magnetopause obtained by the outbound Voyager 1 spacecraft, at a velocity of 11 km/sec, are discussed. Magnetic field and ion data obtained for the period surrounding four magnetopause crossings are presented which reveal energetic anti-sunward flowing ions outside the boundary with a time variability on the order of 400 millisec. These particle intensity variations, observed to vary with frequency, are most likely associated with the particle energization process or with the leakage of magnetospheric protons. The ion flows are considered to have originated sunward of the dawn meridian and were observed to penetrate approximately an ion gyroradius inside the dawn magnetopause.

Lanzerotti, L. J.↗
NASA NTRS1980

Statics of the nightside Jovian plasma sheet

Data are analyzed from the low energy charged particle (LECP) and magnetic field (MAG) experiments on the Voyager 2 spacecraft that demonstrate that the configuration of the Jovian plasma sheet at distances of about .80 to about 120 Jupiter radii is determined by ions (protons and heavier nuclei) of energies greater than approximately 30 keV. The energy densities of these ions are sufficient to provide the diamagnetic depressions in the magnetic field strengths observed as the spacecraft crossed the Jovian plasma sheet. The particle bulk direction of motion is predominantly across the local magnetic field, consistent with that expected from corotation of the planetary magnetic field.

Lanzerotti, L. J.↗
NASA NTRS1971

Quiet-time observation of a coherent compressional Pc-4 micropulsation at synchronous altitude

During a magnetically quiet interval the magnetic-field intensity and energetic electron fluxes at ATS 1 exhibited coherent modulations having a frequency of 33.8 cph and a duration of approximately 40 oscillations. The electron fluxes and the magnetic field oscillated in phase. The field perturbation reached 8 jamma (peak to peak) in the direction of the unperturbed geomagnetic field. The transverse component of the field perturbation was practically zero. The characteristics of the observed oscillations appear compatible with those of a compressional excitation of the outer magnetosphere. The substantially radial normal mode is perhaps driven by a bounce-resonant interaction with the 15-keV protons that populate the quiet-day ring current.

Paulikas, G. A.↗