Engineering topics
Publications and source records attributed to Shelley, E. G..
The He(2+) and He(+) radial profiles measured by the Giotto mass spectrometer on the inbound trajectory to comet Halley are compared to a simple 1-dimensional charge exchange model. Results indicate that charge exchange alone cannot account for the observed radial profiles of He(2+) and He(+).
An analysis is performed of all plasma sheet data collected in 1978-79 in order to discern statistical trends in the data. Attention is focused on the bulk parameters of 0.1-16 keV/e plasma sheet ions detected by the Plasma Composition Experiment on the ISEE 1 satellite. The data were collected at 10-23 earth radii, and are averaged for various levels of activity in the AE index. Solar H(+) and He(2+) ions dominate during quiet periods and possess energies similar to those of the solar wind when the quiet period lasts several hours. Increasing AE index values eventually lead to a replacement of the solar ions with terrestrial ions, particularly O(+), which can have an average energy density of 3-4 keV/e at every activity level. The solar ions, however, increase in energy as their density decreases. The O(+) density is highest near the local midnight and becomes the most numerous during highly disturbed conditions. Finally, the O(+) density was observed to increase by a factor of three over the monitoring period, possibly due to enhanced solar EUV radiation.
The transfer of mass from the solar wind to the magnetosphere and its transport and energization within the magnetosphere are investigated. Lithium atoms released on September 11 and 20, 1984 are utilized as the tracers in this study. The components and capabilities of the Charge Composition Explorer, which are to measure magnetospheric ion composition, are described. The data collected is analyzed and it is observed that Li ions did not enter the magnetosphere in sufficient quantities to be distinguished from the background particles. The modeling of solar wind and magnetosheath transport of Li ions is examined; more than 20 percent of the Li released on September 11, and 50 percent of the Li released on September 20 are mapped to the area around the stagnation point of the magnetopause.
In the decade and a half since the initial discovery that the earth's own ionosphere could at times contribute measurably to the hot plasma in the magnetosphere, significant progress has been made in both current knowledge and understanding of this connection. It is now known that ions of ionospheric origin are found in all major regions of the magnetosphere and at its boundaries. The source region in the ionosphere and the acceleration and transport processes involved in coupling the cold ionospheric plasma to the hot magnetospheric plasma are complex and variable. The large scale morphology of the ionospheric outflow and its distribution throughout the magnetosphere is now understood and progress is being made in the understanding of the fundamental physical processes involved. In this paper attention is given to the large scale morphology and current understanding of the sources for ionospheric ions found in various regions of the magnetosphere and their transport.
Simultaneous high-time-resolution plasma-wave and ion-composition measurements obtained with DE-1 during a magnetospheric-cusp crossing on March 15, 1984 and during an evening auroral-zone crossing on January 4, 1984 are reported. The data are presented graphically and characterized in detail, with a focus on the transverse energization of H(+) and O(+) ions. An O(+) distribution observed during the cusp crossing is shown to be well represented by a bi-Maxwellian distribution with temperatures 180 eV parallel and 250 eV perpendicular to the local magnetic field and a bulk flow velocity of 27 km/s up the magnetic-field line. In the auroral-zone data a simultaneous transverse-energy increase is detected in both H(+) and O(+) components in the presence of plasma-wave emissions at multiples of the hydrogen gyrofrequency.
Selected S3-3 satellite ion-mass-spectrometer observations of upward-flowing 0.5-16-keV terrestrial ions in the auroral zones at altitudes 2000-8000 km are presented graphically and analyzed. The data are shown to support an interpretation in which ion conics are first formed at lower altitudes (by a mechanism which provides more energy to heavier ions) and then accelerated upward through a potential drop; outside these regions ion conics may be generated by mechanisms which are independent of ion mass.
Observations of terrestrial-ion outflow obtained at 0.01-17 keV with the DE-1 energetic-ion composition spectrometer during 1981-1984 are compiled in graphs and analyzed. Long-term variations of the O(+) outflow rate - but not of the H(+) rate - at both magnetically active and quiet times are shown to be well correlated with the declining solar radio flux, the rate in 1983-1984 being only about half that for 1981-1982. Both outflow rates are found to increase exponentially with the Kp index, being 30 and 5 times greater, respectively, at Kp = 6 or more than at Kp = 0. The role of perpendicular ion-acceleration mechanisms at low altitudes is discussed.
An ion-upflow event over the northern auroral zone during a small magnetic storm on August 24, 1976 is characterized on the basis of S3-3 satellite ion-mass-spectrometer observations at 0.5-16 keV. The data are presented in tables, graphs, and diagrams and analyzed in detail. The distributions of upward-flowing O(+) and H(+) associated with parallel electric fields below the satellite are shown to have transverse temperatures of about 1 keV and 0.1 keV, respectively, while the corresponding parallel temperatures were about 1 keV and 0.6 keV; the average energy of the O(+) ions is found to be 2-3 times greater than that of the H(+) ions in the acceleration regions. Possible interpretations of these findings are discussed.
The upflow of ionospheric ions along auroral field lines is investigated on the basis of nearly simultaneous particle measurements obtained with DE-1 at 9000-15,000 km and DE-2 at 400-800 km during four auroral conjunction events in 1981. The data are presented in extensive graphs and maps and characterized in detail. The distributions of the upflowing ions are shown to be consistent with acceleration of a Maxwellian by a parallel electric field, but from the energy levels involved (hundreds of eV) it is inferred that an ionospheric source is being heated within or above the acceleration region, possibly by an ion two-stream instability.
Data acquired from the Dynamics Explorer I Energetic Ion Composition Spectrometer in the period from September 1981 to May 1984 are used to determine the magnitude of the terrestrial ion outflow in the 0.01-17 keV/el range. The data are also employed to investigate the mass composition and topology (local time and invariant latitude distributions) of the ion outflow, as well as the outflow's magnetic activity dependence and long-term variation. The relative importance of auroral versus polar cap upflowing ions as a source of energetic plasma for various parts of the magnetosphere is examined.
In the investigation conducted by Yau et al. (1984), the occurrence frequency distribution of upflowing ionospheric ions (UFI) in the auroral and polar cap ionosphere up to 23,300 km altitude was determined using the Energetic Ion Composition Spectrometer (EICS) data acquired in the first orbital cycle (18 months) of Dynamics Explorer 1 (DE 1). The present paper is concerned with the seasonal and long-term variations in the occurrence and composition characteristics of upflowing ions. The observed solar cycle and seasonal dependences of upflowing ionospheric ion occurrence morphology are summarized schematically in a graph. It is found that the acceleration altitude of O(+) UFI is modulated by the atmospheric scale height, which increases with increasing solar activity (EUV flux). The O(+) UFI occurrence frequency (and hence O(+) outflow) increases at solar maximum.
The Hot-Plasma Composition Experiment (HPCE) on the AMPTE-CCE spacecraft consists of an energetic ions-mass spectrometer and an electron background-environment monitor (EBEM). The mass spectrometer covers the entire mass per charge range from below 1 to greater than 150 amu/e and the energy per charge range from 0 eV/e (spacecraft potential) to 17 keV/e. The EBEM measures electrons between 50 eV and 25 keV in eight broad energy bands. The ion and electron data are processed into color spectrogram formats for the data pool.
Observations from the Hot Plasma Composition Experiment on the AMPTE/CCE spacecraft during the magnetic storm of 4-5 September 1984 reveal that significant injection of ions of terrestrial origin accompanied the storm development. The compression of the magnetosphere at storm sudden commencement carried the magnetopause inside the CCE orbit clearly revealing the shocked solar wind plasma. A build up of suprathermal ions is observed near the plasmapause during the storm main phase and recovery phase. Pitch angle distributions in the ring current during the main phase show differences between H(+) and O(+) that suggest mass dependent injection, transport and/or loss processes.
Compositional studies of the equatorial distributions of ring current ions during the September 4, 1984 magnetic storm have been made possible by comprehensive energy, charge state, and mass coverage data from the Charge Composition Explorer satellite. An examination of ion spectra at an L value of about 4 on September 5, in the local evening sector, shows that energy density was dominated by protons, with O ions contributing about 27 percent at the peak of about 150 keV, while He ions contributed less than about 2 percent. September 6 ion spectra, taken during the recovery phase of the storm, indicate that ion densities at more than 20 keV had decreased markedly, and that the ring current energy density was primarily provided by protons.
Plasma, magnetic-field, and dc electric-field observations from Dynamics Explorers 1 and 2 are used to investigate the morphology of solar-wind ion injection, Birkeland currents, and plasma convection in the morning sector for both positive and negative interplanetary magnetic field (IMF) By components. The results of the study are used to construct a By-dependent global convection model for southward IMF. A significant element of the model is the coexistence of three types of convection cells ('merging cells', 'viscous cells', and 'lobe cells'). This model can account for observations of a nearly stationary (in local time) convection 'throat', a sunward-antisunward convection reversal zone at the polar-cap boundary in both the morning and afternoon quadrants, the morphology of solar-wind ion injection and transport in the mid-altitude polar cusp, and the By-dependent dawn-dusk asymmetry of polar-cap electron fluxes.
Instruments on board the Dynamics Explorer (DE) 1 and 2 spacecraft have been used to investigate the characteristics of a very low-energy (less than 10 eV) outflow of O(+) ions at high altitudes over the polar cap. The measured O(+) outflow has a relatively high Mach number (2-6) and a flux of about 2 x 10 to the 8th/(sq cm s). A statistical study using 50 orbits of retarding ion mass spectrometer data indicates that the outflows occur during active magnetic conditions, lasting for several hours over large areas of the polar cap. The observations are then discussed and analyzed in a framework based on polar wind models with particular attention paid to the new information obtained by the DE 2 Fabry-Perot interferometer, and the impact these flows have on the composition of the magnetosphere. The observed suprathermal outflow of O(+) suggests a scenario requiring both significant compositional changes in the high latitude thermosphere and significant heating of the ions and electrons in the topside ionoshpere.
Shelley et al. (1972) have first reported that ions of terrestrial origin might represent a nonnegligible component of the hot magnetospheric plasmas. The present paper is concerned with those observational results which provide keys to the circulation of energetic magnetospheric ions of terrestrial origin, taking into account ions having energies greater than approximately 10-100 eV. It is pointed out that these are the ions which might be expected to circulate through the plasma sheet. On the basis of the observed ion composition of plasma storage regions (the plasma sheet and ring current) and the source and transport regions (auroral zone acceleration region, polar cap, boundary layers and magnetotail lobes), it is concluded that during magnetically active periods the primary circulation of energetic terrestrial ions is directly from the auroral acceleraton region into the plasma sheet boundary layer and central plasma sheet.
Energetic ion composition spectrometer data gathered on hybrid conical ion distributions by the Dynamics Explorer 1 in the topside ionosphere are reported. The observed ion distributions were field-aligned and upward flowing, with energies up to 5 keV. Increases in ion energy were accompanied by a departure from field-alignment and a cone patterned upward flow, with the apex in the auroral field lines and the cone angle widening upward as the energy increased. Both transverse and parallel accelerations were imparted to the ions, with the transverse heating occurring in a 5000 km extent region centered at 18,000 km altitude. A bi-Maxwellian distribution, a temperature of 1.2 keV and a 260 eV parallel temperature were found at the top of the region.