Engineering topics
Publications and source records attributed to Reiff, P. H..
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.
Two mechanisms have been proposed for solar wind particle injection at the dayside magnetospheric cusps: magnetic merging and cross-field diffusion. These two mechanisms are experimentally distinguishable in that they produce different latitudinal distributions of particles penetrating to the low-altitude cusp. An examination of proton and electron measurements obtained by the AE-C satellite in the low-altitude dayside cusp reveals evidence of both types of injection processes. A majority of the injection events, especially the more intense fluxes, are best explained by a merging injection model in which cusp particles are confined to the poleward side of the last closed field line and have a characteristic energy that decreases with increasing latitudinal distance from the last closed field line. Less frequent and less intense injection events are better explained in terms of a diffusive injection of cusp particles onto closed dayside field lines with a characteristic energy that increases with increasing latitudinal distance from the last closed field line. Although diffusion appears to be quantitatively less important than merging in terms of the instantaneous particle injection rate, cross-field diffusion nevertheless appears to proceed at an unexpectedly fast rate, possibly exceeding the Bohm diffusion limit.
Calculations of the magnetic shadow zones of lunar-based particle detectors are extended to include the effects of local remanent magnetic fields. At the Apollo 14 site, the local magnetic field is approximated as that of a dipole. Numerically calculated open and shadowed zones are shown to be in agreement with quiet-time plasma-sheet observations of the charged-particle lunar-environment experiment. An analysis of three storm-time observations indicates that magnetic shadowing can significantly alter the near-lunar-surface electrostatic potential distribution.
The problem of particle shadowing by the lunar surface is examined. Shadow zones are obtained analytically for small-aperture detectors on an infinite flat surface and are shown to be in good agreement with those obtained by numerical trajectory tracing. The shadow zones cover about half of all possible external field orientations for a vertical detector, which may result in serious underestimations of the frequency of observation of a particular plasma region. Shadowing may cause wide variations between observed and actual pitch angle distributions even in the case of multiple- or large-aperture detectors. Since the particle flux can be considered approximately isotropic only for magnetic fields within 35 deg of the surface normal, the electron flux to the surface may be overestimated in current balance calculations ignoring the magnetic field direction. In addition, photoelectrons may be returned to the surface by the magnetic field.
A study was made of the electron population in the earth's magnetosheath at lunar distance. The data used were collected by the Apollo 14 charged particle lunar environment experiment (CPLEE) during four inbound (dusk) and three outbound (dawn) passages of the moon through the magnetosheath. The magnetotail has a diameter of 52 earth radii, while the bow-shock cross section is about 91 earth radii. The average boundary locations computed from the complete data set are consistent with the prediction of fluid dynamics. The electron characteristics for the two least-disturbed passages are presented in detail. An examination of the energy spectra shows that a high-energy (200-2000 eV) tail is superimposed on the expected low-energy (40-200 eV) magnetosheath distribution. It is argued that the high-energy magnetosheath electron population originates at the bow shock, rather than from the plasma sheet.
Data from the Charged Particle Lunar Environment Experiment (CPLEE), at the Apollo 14 site, are used to investigate the interactive properties of the plasma sheet and the lunar photoelectron layer. It is shown that the predictions of the Guernsey-Fu model are compatible with SIDE but not CPLEE observations. The apparent contradiction is resolved by fitting the remanent magnetic field to that of a dipole buried about 1.1 km beneath the surface. In this case a charge separation layer must form above the instrument due to the different rigidities of plasma sheet electrons and protons. The qualitative properties of the charge separation layer needed to reconcile CPLEE and SIDE observations are presented.