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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Studies of conjugate plasma convection in the vicinity of the Harang discontinuity

This paper presents two case studies of the large-scale nightside ionospheric plasma convection observed in the two polar regions utilizing HF backscatter radars. The times at which the nightside flow reversal (the Harang discontinuity) occurs is seen to differ by several hours between the two study periods and between the two hemispheres. Flow reversal appeared simply to be shifted to later magnetic times in the Southern Hemisphere, while the evening westward flow was disrupted by the occurrence of eastward flow ahead of the Harang discontinuity in the Northern Hemisphere.

Dudeney, J. R.↗
NASA NTRS2003

Pressure Balance at Mars and Solar Wind Interaction with the Martian Atmosphere

The strongest crustal fields are located in certain regions in the Southern hemisphere. In the Northern hemisphere, the crustal fields are rather weak and usually do not prevent direct interaction between the SW and the Martian ionosphere/atmosphere. Exceptions occur in the isolated mini-magnetospheres formed by the crustal anomalies. Electron density profiles of the ionosphere of Mars derived from radio occultation data obtained by the Radio Science Mars Global Surveyor (MGS) experiment have been compared with the crustal magnetic fields measured by the MGS Magnetometer/Electron Reflectometer (MAG/ER) experiment. A study of 523 electron density profiles obtained at latitudes from +67 deg. to +77 deg. has been conducted. The effective scale-height of the electron density for two altitude ranges, 145-165 km and 165-185 km, and the effective scale-height of the neutral atmosphere density in the vicinity of the ionization peak have been derived for each of the profiles studied. For the regions outside of the potential mini-magnetospheres, the thermal pressure of the ionospheric plasma for the altitude range 145-185 km has been estimated. In the high latitude ionosphere at Mars, the total pressure at altitudes 160 and 180 km has been mapped. The solar wind interaction with the ionosphere of Mars and origin of the sharp drop of the electron density at the altitudes 200-210 km will be discussed.

A M Krymskii↗
NASA NTRS1991

Magnetization of the ionospheres of Venus and Mars - Results from radio occultation measurements

Remote sensing radio occultation measurements are used here to study magnetization of the ionospheres of Venus and Mars. For Venus, the measurements yield results on frequency of occurrence of magnetization during solar maximum that are similar to those obtained from Pioneer Venus in situ magnetic field measurements. During solar minimum, magnetization of the Venus ionosphere is more pervasive than at solar maximum. Magnetization extends to higher solar zenith angles and appears stronger than at solar maximum. These results confirm that during solar minimum the high solar wind dynamic pressure state is more prevalent at Venus because the ionospheric plasma pressure is weaker than at solar maximum. Comparison of a large number of electron density profiles of Mars with those of Venus shows an absence of the ledge and disturbed topside plasma observed in the Venus profiles. These results do not constitute evidence against magnetization of the ionosphere of Mars.

Woo, Richard↗
NASA NTRS2003

Global Scale Observations of Ionospheric Instabilities from GPS in Low Earth Orbit

The GPS receiver used for navigation on the Space Shuttle exhibits range rate noise which appears to result from scintillation of the satellite signals by irregularities in ionospheric plasma. The noise events cluster in geographic regions previously identified as susceptible to instability and disturbed ionospheric conditions. These mechanisms are reviewed in the context of the GPS observations. Range rate data continuously monitored during the free orbiting phase of several space shuttle missions reveals global scale distribution of ionospheric irregularities. Equatorial events cluster +/- 20 degrees about the magnetic equator and polar events exhibit hemispheric asymmetry suggesting influence of off axis geomagnetic polar oval system. The diurnal, seasonal and geographic distribution is compared to previous work concerning equatorial spread F, Appleton anomaly and polar oval. The observations provide a succinct demonstration of the utility of space based ionospheric monitoring using GPS. The susceptability of GPS receivers to scintillation represents 'an unanticipated technical risk not factored into the selection of receivers for the United States space program.

Kramer, Leonard↗
NASA NTRS1977

Nuclear burst plasma injection into the magnetosphere and resulting spacecraft charging

The passage of debris from a high altitude ( 400 km) nuclear burst over the ionospheric plasma is found to be capable of exciting large amplitude whistler waves which can act to structure a collisionless shock. This instability will occur in the loss cone exits of the nuclear debris bubble, and the accelerated ambient ions will freestream along the magnetic field lines into the magnetosphere. Using Starfish-like parameters and accounting for plasma diffusion and thermalization of the propagating plasma mass, it is found that synchronous orbit plasma fluxes of high temperature electrons (near 10 keV) will be significantly greater than those encountered during magnetospheric substorms. These fluxes will last for sufficiently long periods of time so as to charge immersed bodies to high potentials and arc discharges to take place.

Pavel, A. L.↗
NASA NTRS2010

Observed Coupling Between the International Space Station PCU Plasma and a FPMU Langmuir Probe Facilitated by the Geomagnetic Field

Electrical charging of the International Space Station (ISS) is a matter of serious concern resulting from the possibility of vehicle arcing and electrical shock hazard to crew during extravehicular activity (EVA). A Plasma Contactor Unit (PCU) was developed and integrated into ISS in order to control the ISS floating potential, thereby, minimize vehicle charging and associated hazards. One of the principle factors affecting ISS electrical charging is the ionosphere plasma state (i.e., electron temperature and density). To support ISS electrical charging studies a Floating Potential Monitoring Unit (FPMU) is also integrated into ISS in order to measure the ionosphere properties using Langmuir probes (LP). The FPMU was located on the Starboard side of ISS. The PCU is located near the center of ISS with its plasma exhaust pointed to port. From its integration on ISS in 2006 through November of 2009, the FPMU data exhibited nominal characteristics during PCU operation. On November 21, 2009 the FPMU was relocated from the Starboard location to a new Port location. After relocation significant enhanced noise was observed in both the LP current-voltage sweeps and the derived electron temperature data. The enhanced noise only occurred when the PCU was in discharge and at unique and repeatable locations of the ISS orbit. The cause of this enhanced noise was investigated. It was found that there is coupling occurring between the PCU plasma and the FPMU LP. In this paper we shall 1) present the on-orbit data and the presence of enhanced noise, 2) demonstrate that the coupling of the PCU plasma and the FPMU measurements is geomagnetically organized, 3) show that coupling of the PCU plasma and the FPMU is primarily due to and driven by particle-wave interaction and 4) show that the ionosphere conditions are adequate for Alfven waves to be generated by the PCU plasma.

Hartman, William↗
NASA NTRS1976

Longitudinal asymmetry of the Jovian magnetosphere and the periodic escape of energetic particles

An earlier model of the Jovian magnetosphere is utilized in which the centrifugal stress of corotating plasma distends the outer magnetosphere and opens the tail field. Because of a longitudinal asymmetry in the ionospheric plasma source strength, caused principally by the nonaxisymmetric surface field, the closed-field region in the tail expands and contracts with the rotation period, resulting in a 10-hour modulation of the flux of energetic particles escaping from the magnetosphere into interplanetary space.

Hill, T. W.↗
NASA NTRS1986

Solar wind control of the Geomagnetic Mass Spectrometer

Evidence from Dynamics Explorer retarding-ion mass-spectrometer data collected between 1981 and 1983 for the mass dispersion of ionospheric plasma in the polar cap, known as the Geomagnetic Mass Spectrometer, is discussed, and implications of this new source of ionospheric ions for the magnetosphere are considered. A localized source of energization of ionspheric H(+), He(+), O(+) and N(+) ions in the polar cusp yields a source of upswelling plasma that is transported into the magnetosphere, and equal heating of the ion species results in field-aligned flow velocities which are inversely proportional to the square root of the ion mass. The present phenomenon is produced by the resulting velocity filter effect of solar-driven ExB ion convection. The influence of solar wind conditions on the outflow via the polar cap ExB convection pattern is also discussed.

Waite, J. H., Jr.↗
NASA NTRS1986

Relationship of the interplanetary electric field to the high-latitude ionospheric electric field and currents Observations and model simulation

The electrical coupling between the solar wind, magnetosphere, and ionosphere is studied. The coupling is analyzed using observations of high-latitude ion convection measured by the Sondre Stromfjord radar in Greenland and a computer simulation. The computer simulation calculates the ionospheric electric potential distribution for a given configuration of field-aligned currents and conductivity distribution. The technique for measuring F-region in velocities at high time resolution over a large range of latitudes is described. Variations in the currents on ionospheric plasma convection are examined using a model of field-aligned currents linking the solar wind with the dayside, high-latitude ionosphere. The data reveal that high-latitude ionospheric convection patterns, electric fields, and field-aligned currents are dependent on IMF orientation; it is observed that the electric field, which drives the F-region plasma curve, responds within about 14 minutes to IMF variations in the magnetopause. Comparisons of the simulated plasma convection with the ion velocity measurements reveal good correlation between the data.

Clauer, C. R.↗
NASA NTRS1978

A self-consistent model of a corotating Jovian magnetosphere

In the rotation-dominated model of the Jovian magnetosphere, proposed in the present paper, the plasma current distribution is dynamically consistent with the magnetic field. The model is constructed under the assumptions of an ionospheric plasma source without pitch angle scattering; loss-free radiation transport through flux tube interchange diffusion; and a static balance between centrifugal force and magnetic stress. Using these assumptions, a dynamic equation is derived for a self-consistent field configuration having a single adjustable parameter that is related to the plasma source strength. The equation is solved by an iterative technique. The self-consistent field resembles a radially distorted dipole field, rather than the flat magnetodisk configuration inferred from Pioneer data. The implication is that such a magnetodisk field would require an equatorial plasma source rather than a source at the feet of the field lines.

Carbary, J. F.↗
NASA NTRS1980

Plasma convection in the high-latitude F-region

Plasma convection patterns in the high-latitude F region are examined, and their implications for F region plasma distributions and the magnetosphere-solar wind interaction are discussed. In-situ electric field measurements in the ionospheric plasma above invariant latitudes of 60 deg are presented which show that the dominant plasma motion is one of two-cell convection perpendicular to the magnetic field, with motion directed away from the sun at invariant latitudes above 70-75 deg and return flow at lower latitudes. AE-C data revealing the presence of eastward, rather than antisunward, convection in the polar cap region is also noted. Analysis of the F region plasma distributions that may result from the two convection patterns indicates that total ion concentrations may differ by two or three orders of magnitude in different signatures of the high-latitude F region, and may account for the mid-latitude F region trough. The F region patterns are also shown to imply that in an open magnetosphere, a region of reconnection extends across a substantial portion of the magnetotail, while in a closed magnetosphere, the viscous interaction may weaken as the plasma moves down the tail, or remain strong with the boundary layer extending down the tail. The importance of further measurements of the stability of the F region convection pattern is pointed out.

Heelis, R. A.↗
NASA NTRS1988

A three-dimensional diffusion/convection model of the large scale magnetic field in the Venus ionosphere

A three-dimensinal diffusion/convection model of the dayside Venus ionosphere magnetic field was developed on the basis of previously published one-dimensional diffusion/convection models, and assuming that the field and flow at the upper boundary (in the magnetic barrier) as well as the ionospheric plasma velocity are known. The results indicate that the low-altitude magnetosheath field draping may be distorted by the interaction with the ionosphere in such a manner that there is an apparent 'focusing' of the field toward the subsolar point, caused by the shear in the horizontal velocity between the magnetosheath and ionospheric flows. A comparison of published magnetic-field observations with the present results indicates that the simple nesting of external and internal velocity fields may be a good approximation to global plasma flows near Venus under normal conditions.

Luhmann, J. G.↗
NASA NTRS1981

Magnetosphere-Ionosphere coupling through the auroral acceleration region

An important form of coupling between the magnetosphere and the ionosphere occurs through acceleration mechanisms operative in the high altitude ionosphere on magnetic field lines connecting to the auroral zone. Energetic ion mass spectrometer data from within these auroral acceleration regions are presented to illustrate the characteristics of the mechanisms. Observations of ionospheric plasmas in the ring current, the distant plasma sheet, and the magnetotail lobes are shown illustrating the extent of their circulation and the importance of their contribution to the plasma in each regime. Finally the precipitating plasmas in the auroral region and the extent and peculiar effects of the 0(+) component of that precipitation on the ionosphere are illustrated.

Sharp, R. D.↗
NASA NTRS1992

Ionospheric models for Venus and Mars

The ways in which different models employ the multifluid continuity, momentum, and energy equations to characterize the ionospheres of Mars and Venus on the basis of in situ neutral and ion compositions are discussed. The Venus ionosphere is permeated by large-scale magnetic fields when the solar wind dynamic pressure is high, but is free from such fields under conditions of low solar wind dynamic pressure. Large-scale magnetic fields are nearly always present in the Mars ionosphere. Plasma moves downward on both planets for magnetized conditions, and magnetic flux is carried from the magnetosheath down into the ionosphere. Ohmic dissipation of the currents responsible for the magnetic field takes place deep in the ionospheres of both planets.

Cravens, T. E.↗
NASA NTRS1999

Polar UVI Observations of Auroral Oval Intensifications during a Transpolar Arc Event on December 7, 1996

The evolution of the northern hemisphere aurora is examined during a time when the Interplanetary Magnetic Field (IMF) makes three brief southward excursions after an extended period of northward IMF. POLAR UltraViolet Imager (UVI) provides images of the aurora while DMSP provides in situ measurements of precipitating particles, ionospheric plasma flows and ion density. Substorm-like events are correlated with northward turnings of the IMF, while the intensity of the ionospheric response is correlated with the duration of the southward IMF period prior to the northward turning. Observations indicate that when the transpolar arc reaches the highest latitudes it is located on a spatially narrow region of closed field lines which extends along the noon-midnight meridian. UV observations indicate a connection between the transpolar arc and the nightside auroral enhancements. Precipitating particles associated with both features are attributed to a plasma sheet boundary layer source in the magnetotail implying a magnetospheric connection between the transpolar arc and the nightside auroral oval intensification.

Cumnock, J. A.↗
NASA NTRS2008

Simulating Sources of Superstorm Plasmas

We evaluated the contributions to magnetospheric pressure (ring current) of the solar wind, polar wind, auroral wind, and plasmaspheric wind, with the surprising result that the main phase pressure is dominated by plasmaspheric protons. We used global simulation fields from the LFM single fluid ideal MHD model. We embedded the Comprehensive Ring Current Model within it, driven by the LFM transpolar potential, and supplied with plasmas at its boundary including solar wind protons, polar wind protons, auroral wind O+, and plasmaspheric protons. We included auroral outflows and acceleration driven by the LFM ionospheric boundary condition, including parallel ion acceleration driven by upward currents. Our plasmasphere model runs within the CRCM and is driven by it. Ionospheric sources were treated using our Global Ion Kinetics code based on full equations of motion. This treatment neglects inertial loading and pressure exerted by the ionospheric plasmas, and will be superceded by multifluid simulations that include those effects. However, these simulations provide new insights into the respective role of ionospheric sources in storm-time magnetospheric dynamics.

Fok, Mei-Ching↗
NASA NTRS1983

Mass composition of substorm-related energetic ion dispersion events

The mass dependent characteristics in two ion dispersion events is studied using data obtained by an ion mass spectrometer flown onboard the SCATHA (P78-2) spacecraft. It is found that the dispersion events are associated with substorm activity and that the dispersing ions originated in the dusk-midnight sector near the time of substorm onset. The question of the source of the dispersing plasma is examined since the mass spectrometer can discriminate between protons and oxygen. It is shown that a local injection of ionosphere plasma near the time of substorm onset can explain some of the signatures in the energetic ion spectra for different masses.

Strangeway, R. J.↗