Engineering topics

Comfort, R. H.

Publications and source records attributed to Comfort, R. H..

At least 55 records · Page 3

NASA NTRS1988

An empirical model of the earth's plasmasphere

An empirical model is developed for plasmaspheric low-energy plasma consisting of H(+). The model is developed from a data base derived from measurements taken by the Retarding Ion Mass Spectrometer on the DE-1 satellite. An analytical expression that reproduces the density profiles for moderate geomagnetic activity is given and discussed. This expression reproduces the density fall-off in the ionosphere as well as the sharp density decrease at the plasmapause.

Gallagher, D. 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

Intercomparison among plasma wake models for plasmaspheric and ionospheric conditions

The angular distributions of ions in the wake of a body moving through a space plasma computed from three different models are compared in order to investigate wake current depletion ratios under conditions simulating the topside ionosphere and plasmasphere. Results demonstrate the importance of taking into account the thermal flux at low Mach numbers and the angular acceptance of ion detectors in making theory-experiment comparisons. For all models considered, gradients in the angular variations of the fluxes are shown to be steeper near the wake-ambient interface than closer to the maximum rarefaction region.

Samir, U.↗

NASA NTRS1987

MHD wave breaking in the outer plasmasphere

Empirical models of the average magnetospheric magnetic field, plasma density, and temperature distributions are used to construct a model of the distribution of MHD wave mode speeds within the magnetosphere. A persistent feature of the derived optical structure is a pronounced minimum of the wave speeds in the outer plasmasphere, i.e., a magnetospheric 'shoal'. This feature does not map along magnetic field lines, but is confined to the equatorial region, leading to a positive radial gradient of wave speeds near synchronous orbit. The breaking of earthward propagating disturbances in this region may play an essential role in the formation of the substorm injection boundary and in the creation of equatorially trapped warm ion distributions.

Moore, T. E.↗

NASA NTRS1987

The role of ring current O(+) in the formation of stable auroral red arcs

Observations of thermal and energetic ion populations by the Dynamics Explorer 1 satellite in the magnetospheric energy source region as well as nearly simultaneous Langmuir probe measurements of enhanced electron temperatures by Dynamics Explorer 2 within the stable auroral red (SAR) arc at F region heights are used to examine the role of heavy ions in the formation of SAR arcs. It is found that sufficient energy is transferred to the electron gas at high altitudes via Coulomb collisions between the observed ring current ions and thermal electrons to support the enhanced F region electron temperatures measured on these field lines. The latitudinal variation in the electron heating rates calculated using observed ion populations is consistent with the observed variation in electron temperature across the SAR arc. In all cases, ring current O(+) is the major source of energy for the SAR arcs.

Kozyra, J. U.↗

NASA NTRS1987

Satellite observations of new particle and field signatures associated with SAR arc field lines at magnetospheric heights

Enhancements in thermal ion densities, an oxygen dominated ring current at energies below 17 keV, and invariant latitude-limited bands of intense ELF hiss have been discovered on Stable Auroral Red (SAR) arc field lines at magnetospheric heights. These new signatures were revealed by an examination of 31 coordinated data sets taken simultaneously at magnetospheric and ionospheric heights by the De-1 and -2 satellites during SAR arc traversals within the period September 1981 through April 1982. Data sets from DE-2, for the first time, provide information on the location of a SAR arc (determined by the F region electron temperature enhancement) during the nearly simultaneous passage of these field lines by DE-1 in the magnetosphere. These new high altitude signatures are examined in the context of possible magnetospheric SAR arc energy source mechanisms.

Kozyra, J. U.↗

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

Investigation of low energy space plasma

A statistical study of 1982 data for occurrences of equatorially trapped plasma has been extended. The previous survey, which utilized only the MSFC summary fiche, has been supplemented with the GSFC summary fiche, which has had the effect of substantially improving the late 1982 coverage. It was found that in the post midnight region (1 - 3 LT), the trapped plasma is limited to + or - 5 degrees magnetic latitude, while in the early afternoon (13-15 LT), latitude ranges as high as + or 30 degrees are found. This survey has provided a link to earlier ATS-6 and ISEE studies of pancake distributions. Although the most energetic, and most anisotopic plasmas are trapped within a few degrees of the equator, the results of these equatorial interactions extend substantially along the magnetic field line in the afternoon and dusk region and these high latitude extensions were previously studied by the Huntsville group. Results of this study were incorporated into a revision of the equatorial ion paper, which has been resubmitted and accepted for publication.

Comfort, R. H.↗

NASA NTRS1986

Space plasma research

Four basic areas were covered: development of analysis techniques and software and numerical simulations; data analysis and interpretation; spacecraft sheath studies; and laboratory studies. The important details were documented in terms of either appropriate software documentation or publication in referred publication, conference proceeding and technical reports. The major accomplishments are summarized, followed by a chronological listing of the publications and presentations which resulted from the research.

Comfort, R. H.↗

NASA NTRS1986

Space plasma research

Temperature and density analysis in the Automated Analysis Program (for the global empirical model) were modified to use flow velocities produced by the flow velocity analysis. Revisions were started to construct an interactive version of the technique for temperature and density analysis used in the automated analysis program. A sutdy of ion and electron heating at high altitudes in the outer plasmasphere was initiated. Also the analysis of the electron gun experiments on SCATHA were extended to include eclipse operations in order to test a hypothesis that there are interactions between the 50 to 100 eV beam and spacecraft generated photoelectrons. The MASSCOMP software to be used in taking and displaying data in the two-ion plasma experiment was tested and is now working satisfactorily. Papers published during the report period are listed.

Comfort, R. H.↗

NASA NTRS1986

Observations of low-energy ions in the wake of a magnetospheric satellite

Measurements of low-energy ions made by the retarding ion mass spectrometer (RIMS) onboard the Dynamics Explorer 1 (DE 1) satellite are used to study some aspects of 'body-plasma interactions' in the terrestrial plasmasphere. Preliminary results are presented, yielding the degree of H+ and He+ ion depletion in the wake of the satellite in terms of specific and average ion Mach numbers, average ion mass, body size normalized to ionic Debye length, and body potential normalized to ion thermal energy. Some results from the RIMS measurements are compared with relevant results from the Explorer 31 and the Atmosphere Explorer C ionospheric satellites. Wake depletion is found to vary approximately linearly for small bodies (R-sub-Di less than about 12) and exponentially for large bodies (R-sub-Di greater than 50).

Samir, U.↗

NASA NTRS1986

Thermal ion heating in the vicinity of the plasmapause: A Dynamics Explorer guest investigation

The ion thermal structure of the plasmasphere was investigated in a series of experiments. It appears that energy may be generally available to ion and electrons in the vinicity of the plasmapause from Coulomb interactions between ambient thermal plasma and low energy ring current and suprathermal ions, particularly O+. The amount of energy transferred depends on the densities and energies of each of the components. The spatial distribution of heating in turn depends critically on the spatial distribution of the different populations, especially on the density gradients. The spatial distribution of the thermal plasma is found to vary significantly on a diurnal time scale and is complicated by the plasmasphere erosion and refilling processes associated with magnetic activity and its aftermath. Thermal ion composition also appears to be influenced by the heating taking place, often increasing the heavy ion population in the vicinity of the plasmapause. The observations of equatorial heating near the plasmapause in the presence of equatorial noise also raise the likelihood of a wave source of energy. It is not unreasonable to expect that both particle and wave heat sources are significant, although not necessarily at the same times and places.

Comfort, R. H.↗

NASA NTRS1986

Plasmaphere and plasmapause region characteristics as measured by DE-1

Thermal ion composition measurements by the retarding ion mass spectrometer (RIMS) on the Dynamics Explorer-1 have revealed new and intriguing features of the thermal ion distributions in the plasmasphere and plasmapause regions. Some of the interesting new findings include: the presence of intense fluxes of heated and equatorially-trapped light ions within the plasmapause region; the existence of a heavy ion 'torus' or 'shell' in the outer plasmasphere; and the relatively stable nature of the He(+)/(H+) concentration ratio within the plasmasphere. The relatively short orbital period of DE-1 has also allowed improved observations on the formation of the new outer plasmasphere during the recovery of geomagnetic storms. Statistical studies of the plasmaspheric density structure and boundaries are beginning to reveal a picture of their relation to other magnetospheric boundaries, such as the inner edge of the electron plasma sheet, and trends in the internal density structure of the plasmasphere.

Horwitz, J. L.↗

NASA NTRS1986

Plasmasphere thermal structure as measured by ISEE-1 and DE-1

Characteristics of plasmaspheric ion thermal structure are presented from a statistical survey of low-energy of ion measurements made by the retarding ion mass spectrometer (RIMS) on the DE-1 satellite. Morning and evening results are compared to illustrate diurnal trends. Typical day side temperature range from about 4000 K in the inner plasmasphere to over 10,000 K in the outer plasmasphere, while corresponding evening side temperatures range from near 2000 K to over 10,000 K. Magnetic activity is found to affect the morning and evening sides somewhat differently. Temperatures are found to remain constant or increase with altitude along magnetic field lines, depending on local time and L shell. Thermal equilibrium between H(+) and He(+) prevails to a high degree throughout the plasmasphere. Ion temperatures from the Plasma Composition Experiment (PCE) on ISEE-1 are generally consistent with those from DE-1/RIMS, but are lower and tend to indicate more large scale structure on the day side.

Comfort, R. H.↗

NASA NTRS1985

Auroral thermosphere temperatures from observations of 6300 A emissions

Doppler temperatures determined from observations of the atomic oxygen OI 6300 A line during March 1984 at the University of Alaska/Fairbanks are presented. Temperatures are obtained from Fabry-Perot Interferometer pressure scans using a Fourier transform smoothing and fitting technique; this technique is presented in detail. The temperatures and the spread in the temperatures are consistent from day to day. On the clear nights of March 10 to 13, the temperatures were 800, 750, 750 and 800 K, respectively, with a spread of + or - 100 K. These temperatures are compared to the MSIS (84) model atmosphere for similar geomagnetic conditions and found to be in general agreement; they are also consistent with results obtained by other investigators.

Bird, J. C.↗

NASA NTRS1985

Plasma and magnetospheric research

Several programs and variations have been developed to determine statistical means of different plasma parameters when binned in different variables. These parameters include temperature, densities and spacecraft potentials for any of the ion species, as well as ratios of these variables for any other ion species to the corresponding variable for H(+). The variables for binning include L, radial distance, and geomagnetic latitude; and separate statistics are automatically run for local morning and local evening data. These programs all run from output files from the plasma parameter thin sheath analysis program. A variant program also bins for magnetic activity, using either Kp or Dst, which requires an additional magnetic activity input file. These programs can be run either interactively or in batch mode, using file listings generated by a DIRECTORY command. In addition to printed output, these programs generate output files which can be used to plot the results. Programs to plot these averaged data are under development.

Comfort, R. H.↗

NASA NTRS1985

DE 1 RIMS operational characteristics

The Retarding Ion Mass Spectrometer (RIMS) on the Dynamics Explorer 1 spacecraft observes both the thermal and superthermal (50 eV) ions of the ionosphere and inner magnetosphere. It is capable of measuring the detailed species distribution function of these ions in many cases. It was equipped with an integral electrometer to permit in-flight calibration of the detector sensitivities and variations thereof. A guide to understanding the RIMS data set is given. The reduction process from count rates to physical quantities is discussed in some detail. The procedure used to establish in-flight calibration is described, and results of a comparison with densities from plasma wave measurements are provided. Finally, a discussion is provided of various anomalies in the data set, including changes of channeltron efficiency with time, spin modulation of the axial sensor heads, apparent potential differences between the sensor heads, and failures of the radial head retarding potential sweep and of the -Z axial head aperture plane bias. Studies of the RIMS data set should be conducted only with a thorough awareness of the material presented here, or in collaboration with one of the scientists actively involved with RIMS data analysis.

Olsen, R. C.↗