Engineering Papers⌕ Search

Engineering topics

Chappell, C. R.

Publications and source records attributed to Chappell, C. R..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Thermal He(+) in the plasmasphere - Comparison of observations with numerical calculations

Observations made by the retarding ion mass spectrometer on the Dynamics Explorer-1 satellite are used to study the relationship between He(+) and H(+). The observations are compared to theoretical values obtained using the field line interhemispheric plasma model (Richards and Torr, 1988). The observations are presented in the form of statistical L shell distributions and density versus L shell profiles. To obtain agreement between the measured and predicted ion temperature, it must be assumed that approximaterly 55 pct of the energy of the ionospheric photoelectron escape flux is deposited in the plasmasphere.

Newberry, I. T.↗
NASA NTRS1989

A three-dimensional numerical model of ionospheric plasma in the magnetosphere

A three-dimensional particle trajectory tracing in empirical models of the geoelectric and geomagnetic fields is used to study the ionospheric contribution to magnetospheric plasma. Various ionospheric outflows are examined and results on ion transport are presented in terms of density, composition, and energy. Results are presented for two opposite magnetospheric configurations, ground state and storm phases. An estimate of the contribution of ionospheric O(+) to the hot plasma sheet is given. The simulation results are compared with observational data.

Delcourt, D. C.↗
NASA NTRS1989

Report from ionospheric science

The general strategy to advance knowledge of the ionospheric component of the solar terrestrial system should consist of a three pronged attack on the problem. Ionospheric models should be refined by utilization of existing and new data bases. The data generated in the future should emphasize spatial and temporal gradients and their relation to other events in the solar terrestrial system. In parallel with the improvement in modeling, it will be necessary to initiate a program of advanced instrument development. In particular, emphasis should be placed on the area of improved imaging techniques. The third general activity to be supported should be active experiments related to a better understanding of the basic physics of interactions occurring in the ionospheric environment. These strategies are briefly discussed.

Raitt, W. J.↗
NASA NTRS1989

Report from magnetospheric science

By the early 1990s, magnetospheric physics will have progressed primarily through observations made from Explorer-class spacecraft, sounding rockets, ground based facilities, and shuttle based experiments. The global geospace science (GGS) element of the International Solar Terrestrial Physics program, when combined with contributions to the ESA Cluster mission and ground based and computer modeling programs, will form the basis for a major U.S. initiative in magnetospheric physics. The scientific objectives of the GGS program involve the study of energy transport throughout geospace. The Cluster mission will investigate turbulence and boundary phenomena in geospace, particularly at high latitudes on the dayside and in the region of the neutral sheet at geocentric distances of about 20 earth radii on the night side of the earth. The current state of knowledge is reviewed and the goals of these missions are briefly discussed.

Burch, J. L.↗
NASA NTRS1989

Polar wind ion bands after neutral sheet acceleration

The transport of polar wind protons from their ionospheric source through the magnetosphere is examined, using three-dimensional particle codes. The trajectory simulations demonstrate the escape of the high-latitude polar wind in the boundary layers during the quiescent magnetosphere, and, in contrast, its trapping in the nightside plasma sheet at times of high Kp. It is shown that the equatorial curvature of the magnetic field lines plays the role of an acceleration filter which yields, during active conditions, an 'ion band'-like precipitation of the polar wind protons characterized by a decrease of the downflowing ion energy with latitude, from several hundred down to a few electron volts. A further comparison between data and computations tends to indicate that, during disturbed times, the dayside originating polar wind provides an important contribution to the hundreds of electron volt downflowing protons in the nightside sector.

Delcourt, D. C.↗
NASA NTRS1989

Features of terrestrial plasma transport

Research concerning the transport and distribution of ionospheric plasma in the magnetosphere are reviewed, stressing the dichotomy in explanations given for the low plasma densities outside the plasmasphere. The convection/hot solar plasma model and the convection/loss model are considered. Observations of global ionospheric outflows are compared with theoretical studies. It is suggested that there is a need for a hybrid model of magnetospheric plasma in which terrestrial plasma is both lost into the solar wind and energized and trapped within the magnetosphere, inflating the geomagnetic field and excluding cold plasma from conjugate regions.

Moore, T. E.↗
NASA NTRS1988

Preliminary statistical survey of plasmaspheric ion properties from observations by DE 1/RIMS

The paper presents mean temperatures and densities of plasmaspheric H(+) ions obtained from observations by the retarding ion mass spectrometer on Dynamics Explorer 1. Composition is shown in terms of ratios of densities of the various ion species to those of H(+). The spatial variations are indicated in terms of L shell profiles, with separate profiles for local morning and evening sides.

Comfort, R. H.↗
NASA NTRS1988

Dynamic evolution of low-energy ions in the terrestrial magnetosphere

Results of a statistical study of low-energy (0-50 eV) field-aligned ion pitch angle distributions for H(+), He(+), and O(+) observed by the Dynamics Explorer retarding ion mass spectrometer instrument are presented. Ion distributions are characterized as uni- and bi-directional field-aligned and bi-directional conic distributions. The spatial relationships of these distributions can be interpreted as dynamic evolution of low-energy ion flow in which injected unidirectional field-aligned streams originating in the nightside auroral zone evolve first into bi-directional flows under the influence of convection in the mirror magnetic field configuration. Characteristic convection times are evaluated with a pitch angle diffusion model in which field-aligned flows evolve into conical distributions through charge exchange loss of particles to the atmosphere during particle mirroring periods.

Giles, B. L.↗
NASA NTRS1987

Space experiments with particle accelerators (SEPAC): Description of instrumentation

SEPAC (Space Experiments with Particle Accelerators) flew on Spacelab 1 (SL 1) in November and December 1983. SEPAC is a joint U.S.-Japan investigation of the interaction of electron, plasma, and neutral beams with the ionosphere, atmosphere and magnetosphere. It is scheduled to fly again on Atlas 1 in August 1990. On SL 1, SEPAC used an electron accelerator, a plasma accelerator, and neutral gas source as active elements and an array of diagnostics to investigate the interactions. For Atlas 1, the plasma accelerator will be replaced by a plasma contactor and charge collection devices to improve vehicle charging meutralization. This paper describes the SEPAC instrumentation in detail for the SL 1 and Atlas 1 flights and includes a bibliography of SEPAC papers.

Taylor, W. W. L.↗
NASA NTRS1987

Heavy ion density enhancements in the outer plasmasphere

The occurrences of density enhancements of thermal heavy ions O(+), O(2+), and N(+) observed on numerous occasions by mass spectrometer aboard the Dynamics Explorer 1 (DE 1) are studied. A statistical study, covering almost 600 passes of DE 1 through the plasmasphere, shows that O(+) and O(2+) enhancements occur over 64 percent of the observed passes, with the highest frequency of occurrence being in the late evening and morning regions. The O(+) enhancements tend to be seen more frequently in the morning, while the O(2+) enhancements are seen more often in the evening. Two models for the generation of the enhancements are described, and the data from the analysis are interpreted in light of these models.

Roberts, W. T., Jr.↗
NASA NTRS1987

The ionosphere as a fully adequate source of plasma for the earth's magnetosphere

The ionospheric contribution of the polar wind and cleft ion fountain at energies less than 10 eV has been added to previously measured sources; this total ion outflow has then been used to calculate the resulting ion density in the different internal regions of the earth's magnetosphere: plasmasphere, plasma trough, plasma sheet, and magnetotail lobes. Using estimated volumes for these regions and an ion residence time characteristic of each region, it is found that the observed magnetospheric densities can be attained in all cases with no contribution from the solar wind plasma. In the case of the plasma sheet the ionospherically supplied density is more than enough to match the observations and even suggests an invisible component of low-energy plasma (less than 10 eV) which has never been observed. A detailed comparison between the calculated ionospheric source effects in the plasma sheet and those recently measured by ISEE shows excellent agreement and suggests a direct polar low-energy ion source for the plasma sheet which has remained unmeasured because of spacecraft potential effects. Although the solar wind is clearly the earth's magnetospheric energy source and energetic solar wind ions are observed in the magnetosphere, these calculations suggest the possibility that the ionospheric source alone is sufficient to supply the entire magnetospheric plasma content under all geomagnetic conditions.

Chappell, C. R.↗
NASA NTRS1987

Plasma observations at the earth's magnetic equator

New observations of particle and wave data from the magnetic equator from the DE 1 spacecraft are reported. The results demonstrate that the equatorial plasma population is predominantly hydrogen and that the enhanced ion fluxes observed at the equator occur without an increase in the total plasma density. Helium is occasionally found heated along with the protons, and forms about 10 percent of the equatorially trapped population at such times. The heated H(+) ions can be characterized by a bi-Maxwellian with kT(parallel) = 0.5-1.0 eV and kT = 5-50 eV, with a density of 10-100/cu cm. The total plasma density is relatively constant with latitude. First measurements of the equatorially trapped plasma and coincident UHR measurements show that the trapped plasma is found in conjunction with equatorial noise.

Olsen, R. C.↗
NASA NTRS1986

Plasma and field observations of a Pc 5 wave event

The particle detector and electric field data collected by the Dynamo Explorer 1 on the Pc 5 wave event encounter on July 14, 1982 are presented, yielding a nearly complete picture of the event. The overall structure of the Pc 5 seems to order the event into two distinct halves, suggesting a temporal or spatial variation of the micropulsation. Thermal plasma measurements showed that the dominant ion throughout both lobes was H(+). Significant quantities of He(+), O(+), N(+), and O(2+) were also observed to be present and rotating together in a plane normal to the magnetic field direction, due to the Pc5 E x B drift. The plasma parameters determined for the two lobes were used in theoretical calculations to predict the period of the observed resonance.

Waite, J. H.↗
NASA NTRS1986

Dual-spacecraft measurements of plasmasphere-ionosphere coupling

An extensive set of plasmaspheric measurements by the DE 1 satellite and ionospheric measurements by the DE 2 satellite are presented. The developments in the ionosphere and plasmasphere during the recovery phase of a magnetospheric storm are described. Isolated profile comparisons are used to indicate some of the structural relations and complexities involving the ionosphere and plasmasphere latitudinal profiles. A transition in the ionospheric electron temperature Te from a relatively smooth profile of low Te at the base of the inner plasmasphere to enhanced and highly structured Te at higher invariant latitudes occurs near or along a plasmaspheric density gradient. Plasmaspheric enhancements of the heavy ions O(+) and O(2+) are often closely aligned with distinct ionospheric Te enhancements.

Horwitz, J. L.↗
NASA NTRS1986

Observations of the flow of H(+) and He(+) along magnetic field lines in the plasmasphere

Based on Retarding Ion Mass Spectrometer data from Dynamics Explorer 1 collected from October 1981 through January 1982, the field-aligned flow of H(+) and He(+) are studied, representing the first direct observation of ion velocities along magnetic field lines at high altitudes of ion velocities along magnetic field lines at high altitudes in the plasmasphere. Downward directed velocities noted in the Northern Hemisphere within 30 deg of the equatorial plane are thought to be interhemispheric flows, and typical velocities are of the order of a few hundred meters per second. Flows of up to 1 km/s in the outer plasmasphere may be associated with refilling, and a summer-to-winter or spring-to-autumn pattern was seen in the flow of both ions, except in the cases of counterstreaming in which He(+) was moving from winter to summer. Counterstreaming in the autumn and winter hemispheres was observed with He(+) flowing upward and H(+) flowing downward.

Chandler, M. O.↗
NASA NTRS1986

Plasma boundaries in the inner magnetosphere

Based principally on data collected aboard the DE 1 and 2 spacecraft during the October 7 to December 1, 1981 period, plasma boundaries in the inner magnetosphere are studied. Results indicate that in the evening sector, the low-energy ion transition and the 100-eV inner edge of the electron plasma sheet are coincident with each other, with the field lines threading the 100-eV equatorward edge of the auroral electron precipitation, and with variations in magnetic activity. A characteristic energy dispersion, observed in the plasma sheet inner edges at 100 eV, 1 keV and 10 keV, with the lower energy boundaries located earthward of the higher energy boundaries, is shown to increase from the midnight sector toward dusk, and to decrease with increasing magnetic activity. In the evening sector, these boundaries are shown to be accurate signatures of the boundary between closed and open convection trajectories, and the characteristic electron energy sheet dispersion is found to be similarly governed by the convection pattern such that the inner edges may be seen as the Alfven layers at those energies.

Horwitz, J. L.↗
NASA NTRS1986

Latitudinal plasma distribution in the dusk plasmaspheric bulge - Refilling phase and quasi-equilibrium state

Very low-energy trapped ions, mostly protons, have been observed in a region of moderate density characteristic of the plasmapause boundary and of the plasmaspheric bulge. The present paper is concerned with an examination of the latitudinal structure of the bulge under quasi-steady conditions and the conditions of the recovery phase. Details regarding the data base are considered along with observations of the morphology and dynamics of the bulge, the latitudinal density distribution in the expanded bulge, the convection scenario during the replenishment phase, and latitudinal effects on plasma characteristics during plasmasphere refilling. The data utilized have been mainly provided by the DE 1 and GEOS 2 spacecraft traveling in two perpendicular planes. It is found that the bulge is a dynamic region, where no reasonable interpretation of the observed density distribution can be achieved without taking into account the mechanism of magnetospheric convection.

Decreau, P. M. E.↗