Engineering topics

Horwitz, J. L.

Publications and source records attributed to Horwitz, J. L..

At least 73 records · Page 4

NASA NTRS1987

Model for the geomagnetic ion spectrometer in the magnetotail lobes

A two-dimensional kinetic tail-lobe ion spectrometer model for the transport of ionospheric ions from the polar-cleft ionosphere into the tail lobes is developed to simulate semiquantitatively the behavior of the observed O(+) ion streams in the magnetotail lobes. The consequences of the present model include: (1) the increase in velocity of the O(+) streams away from the tail midplane and (2) the existence of tongues of O(+) density from the cleft ionosphere into the tail lobes whose distribution configuration depends on the convection electric field and the source thermal energies. These consequences are reasonably consistent with the trends in lobe streams observed by recent spacecraft.

Horwitz, J. L.↗

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

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

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

The tail lobe ion spectrometer

A two-dimensional kinetic 'tail lobe ion spectrometer' model for the transport of ionospheric ions from polar cleft ionosphere into the tail lobes is developed to semiquantitatively simulate the behavior of the observed O(+) ion streams in the magnetotail lobes. The consequences of the present model include: (1) the increase in velocity of the O(+) streams away from the tail midplane; (2) the existence of 'tongues' of O(+) density from the cleft ionosphere into the tail lobes whose distribution configuration depends on the convection electric field and the source thermal energies; and (3) very low parallel thermal energies and speeds in the lobes which are correlated with the parallel ion bulk velocities. These consequences are reasonably consistent with the trends in lobe streams observed by recent spacecraft.

Horwitz, J. L.↗

NASA NTRS1986

Velocity filter mechanism for ion bowl disributions (Bimodal conics)

The 'bowl-shaped' ion distributions in the high altitude auroral region observed by Klumpar et al. (1984) were originally interpreted as being due to a two-stage acceleration involving transverse ion heating and upward-aligned electric field acceleration. In this paper, it is shown that qualitatively similar bowl-shaped distributions can also be formed by transverse heating in a region of finite horizontal extent, followed by essentially adiabatic convective flow to the observation location. The latter stage contributes a velocity-filtering effect which produces some characteristics of the distributions observed. It is suggested it may be possible to use ion species observations to distinguish the mechanism proposed by Klumpar et al. from the alternative mechanism outlined in the present study.

Horwitz, J. L.↗

NASA NTRS1986

Destiny of earthward streaming plasma in the plasmasheet boundary layer

The dynamics of the earth's magnetotail have been investigated, and it has become clear that the plasmasheet boundary layer field lines map into the Region I Field-Aligned Currents (FAC) of the auroral zone. It is pointed out that the role of earthward streaming ions in the plasmasheet boundary layer may be of fundamental importance in the understanding of magnetotail dynamics, auroral zone physics, and especially for ionospheric-magnetospheric interactions. The present paper has the objective to evaluate propagation characteristics for the earthward streaming ions observed in the plasmasheet boundary layer. An investigation is conducted of the propagation characteristics of protons in the plasmasheet boundary layer using independent single particle dynamics, and conclusions are discussed. The density of earthward streaming ions found in the plasmasheet boundary layer should include the ring current as well as the auroral zone precipitaiton and inner plasmasheet regions of the magnetosphere.

Green, J. L.↗

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

Models of the plasmaspheric thermal plasma distribution

Current understanding of the thermal plasma in the atmosphere and its coupling to the ionosphere is reviewed. Existing models appear adequate to explain the gross behavior of the cold thermal plasma, but there remain some vexing problems. Notably, (1) why does the density in flux tubes appear to saturate at lower values than are predicted theoretically, (2) what causes the sunset peak in measured Te, and (3) why does the equatorial plasmapause signature differ in latitude from the ionosphere signatures. The more difficult problem of what happens during the early stages of refilling after a magnetic storm, when the high altitude plasma is likely to be supersonic and collisionless, has received much attention, but the results are not definite. A number of papers have dealt with the interaction of supersonic counterstreaming fluxes and there are now models that can handle the transition from supersonic to subsonic flows although the transition from a collisionless to a collision-dominated plasma remains difficult to deal with.

Richards, P. G.↗

NASA NTRS1986

Transport of accelerated low-energy ions in the polar magnetosphere

Recent satellite observations of low-energy (0-50 eV) ionospheric ions in the polar cap magnetosphere suggest that these ions are injected at the dayside cleft topside ionosphere. Using a two-dimensional kinetic model, several consequences of this ion flow from a narrow cleft source have been simulated and observed. These include: (1) the Kp/convection-dependent filling of the polar magnetosphere with ionospheric heavy ions, in which these ions are 'blown' further into the polar cap magnetosphere from the cleft during high Kp/convection; (2) the mass- and energy-dependent dispersion of these ions, as in a kind of 'geomagnetic spectrometer'; (3) the creation of 'supersonic' ion outflows as a natural velocity-filter effect of this geomagnetic spectrometer; and (4) the 'parabolic flow' of gravitationally bound heavy ions from the cleft ionosphere resulting in downward flow into the polar cap.

Horwitz, J. L.↗

NASA NTRS1985

Supersonic ion outflows in the polar magnetosphere via the geomagnetic spectrometer

Observations of 'supersonic' O(+) outflows by DE-1 in the polar magnetosphere are interpreted as a velocity-filter effect resulting from the transport of these low energy ions from a horizontally narrow source associated with the polar cleft topside ionosphere into the polar cap magnetosphere. Under certain simplifying circumstances, it is shown that the 'Mach number' for the flow is essentially a geometrically determined quantity, approximately the ratio of the horizontal distance of the observation location to the source over the horizontal width of the source. A recently developed two-dimensional kinetic model of ion transport in the polar magnetosphere is used to calculate distribution functions and the associated bulk flow parameters, and these calculated quantities are compared with measured flow parameters from DE-1.

Horwitz, J. L.↗

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

The cleft ion fountain - A two-dimensional kinetic model

The transport of ionospheric ions from a source in the polar cleft ionosphere through the polar magnetosphere is investigated using a two-dimensional, kinetic, trajectory-based code. The transport model includes the effects of gravitation, longitudinal magnetic gradient force, convection electric fields, and parallel electric fields. Individual ion trajectories as well as distribution functions and resulting bulk parameters of density, parallel average energy, and parallel flux for a presumed cleft ionosphere source distribution are presented for various conditions to illustrate parametrically the dependences on source energies, convection electric field strengths, ion masses, and parallel electric field strengths. The essential features of the model are consistent with the concept of a cleft-based ion fountain supplying ionospheric ions to the polar magnetosphere, and the resulting plasma distributions and parameters are in general agreement with recent low-energy ion measurements from the DE 1 satellite.

Horwitz, J. L.↗

NASA NTRS1985

The geomagnetic mass spectrometer - Mass and energy dispersions of ionospheric ion flows into the magnetosphere

Observations of ion flows in the polar magnetosphere, made by the retarding ion mass spectrometer on NASA's Dynamics Explorer (DE) 1, are compared with those made simultaneously in the topside ionosphere by the ion drift meter on the lower-altitude DE 2 spacecraft. The results show the dayside auroral ionosphere to be a significant and highly persistent source of plasma for the magnetosphere. The upwelling ionospheric ions are spatially dispersed, according to both their energy and mass, by the combined actions of the geomagnetic field and the dawn-to-dusk convection electric field, in an effect analogous to the operation of an ion mass spectrometer.

Lockwood, M.↗

NASA NTRS1985

Structure of the plasmapause from ISEE 1 low-energy ion and plasma wave observations

Low-energy ion pitch angle distributions are compared with plasma density profiles in the near-earth magnetosphere using ISEE 1 observations. The classical plasmapause determined by the sharp density gradient is not always observed in the dayside region, whereas there almost always exists the ion pitch angle distribution transition from cold, isotropic to warm, bidirectional, field-aligned distributions. In the nightside region the plasmapause density gradient is typically found, and it normally coincides with the ion pitch angle distribution transition. The sunward motion of the plasma is found in the outer part of the 'plasmaspheric' plasma in the dusk bulge region.

Nagai, T.↗

NASA NTRS1985

The substorm as an internal magnetospheric instability Substorms and their characteristic time scales during intervals of steady interplanetary magnetic field

In a study of the dynamics of dayside aurora, Horwitz and Akasofu (1977) adopted the basic methodology of examining substorms which occurred during intervals when the interplanetary magnetic field was steady. By using this approach, it was possible to remove the obvious ambiguity in the interpretation of dayside auroral dynamics which arises if interplanetary medium variations are not excluded. It is believed that for an understanding of the natural, internal instability behavior of the magnetosphere it will be necessary to employ the same methodology in many 'substorm' studies. The present investigation has the objective to present some examples of substorms occurring during intervals of steady interplanetary magnetic field. Subsequently, the approximate time scales of expansion and recovery for such substorms are determined. The obtained results are compared with a substorm model proposed by Hill and Reiff (1980).

Horwitz, J. L.↗