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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
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NASA NTRS1982

Pioneer 10/11 data analysis of the trapped radiation experiment

The data handling operations and the database produced by the Trapped Radiation Experiment on the NASA Pioneer 10 and 11 spacecraft are outlined. In situ measurements of trapped radiation at both Jupiter and Saturn, the extension of cosmic ray observations to the outer heliosphere, the presence of Jovian electrons in interplanetary space, analyses of the interaction between planetary satellites and the trapped radiation that engulfs them, and further investigations of the radiation enviroments of both planets are reported.

Fillius, W.↗
NASA NTRS1981

Shock-associated low-energy ion enhancements observed by Voyagers 1 and 2

Observations of shock-associated ion enhancements at energies of not less than 30 keV are presented from data gathered by Voyagers 1 and 2. Observations include examples of energetic storm particle events associated with flare-produced shocks and examples of corotating particle events (CPE) associated with forward and reverse shocks that bound corotating interaction regions in the outer heliosphere. Most of the CPE have recurrent double-peaked intensity enhancements showing little or no velocity dispersion at peak intensities, time durations of several days, and soft energy spectra extending up to 5 MeV/nucleon. The lowest energy ion enhancements are confined mainly downstream of the corotating interaction regions with the magnitude and duration of the upstream enhancements increasing with increasing ion energy. The observations are consistent with the dynamical and kinematical effects expected when low energy ions are accelerated at quasi-perpendicular shocks.

Decker, R. B.↗
NASA NTRS1981

The solar modulation of the anomalous helium component from 1965 to 1980 and from 1 to 23 A.U.

The modulation of the anomalous He-4 component is investigated both in time and in space from 1 to 23 AU with the spacecraft network of IMP-8, and Pioneers 10 and 11. The times of appearance and disappearance of the anomalous He-4 are determined, and it is found to have a higher sensitivity to modulation both in time and space than cosmic ray protons and helium of equivalent or lower rigidity. The disappearance of the flux due to modulation progressed radially outward over several months suggests that the source lies in the outer heliosphere, probably beyond 25 AU, and possibly out of the ecliptic.

Garcia-Munoz, M.↗
NASA NTRS1983

Corotating pressure waves without streams in the solar wind

Voyager 1 and 2 magnetic field and plasma data are presented which demonstrate the existence of large scale, corotating, non-linear pressure waves between 2 AU and 4 AU that are not accompanied by fast streams. The pressure waves are presumed to be generated by corotating streams near the Sun. For two of the three pressure waves that are discussed, the absence of a stream is probably a real, physical effect, viz., a consequence of deceleration of the stream by the associated compression wave. For the third pressure wave, the apparent absence of a stream may be a geometrical effect; it is likely that the stream was at latitudes just above those of the spacecraft, while the associated shocks and compression wave extended over a broader range of latitudes so that they could be observed by the spacecraft. It is suggested that the development of large-scale non-linear pressure waves at the expense of the kinetic energy of streams produces a qualitative change in the solar wind in the outer heliosphere. Within a few AU the quasi-stationary solar wind structure is determined by corotating streams whose structure is determined by the boundary conditions near the Sun.

Burlaga, L. F.↗
NASA NTRS1983

Corotating pressure waves without fast streams in the solar wind

Voyager 1 and 2 magnetic field and plasma data are presented which demonstrate the existence of large scale, corotating, non-linear pressure waves between 2 AU and 4 AU that are not accompanied by fast streams. The pressure waves are presumed to be generated by corotating streams near the sun. For two of the three pressure waves that are discussed, the absence of a stream is probably a real, physical effect, viz., a consequence of deceleration of the stream by the associated compression wave. For the third pressure wave, the apparent absence of a stream may be a geometrical effect; it is likely that the stream was at latitudes just above those of the spacecraft, while the associated shocks and compression wave extended over a broader range of latitudes so that they could be observed by the spacecraft. It is suggested that the development of large-scale non-linear pressure waves at the expense of the kinetic energy of streams produces a qualitative change in the solar wind in the outer heliosphere. Within a few AU the quasi-stationary solar wind structure is determined by corotating streams whose structure is determined by the boundary conditions near the sun. Previously announced in STAR as N83-19694

Burlaga, L. F.↗
NASA NTRS1985

Latitude dependence of co-rotating shock acceleration

Energetic particle observations in the outer heliosphere (approx 12 A. U.) by the LECP instruments on the Voyager 1 and Voyager 2 spacecraft are discussed that show a definite latitude dependence of the number and intensity of particle enhancements produced by corotating interplanetary regions during an interval when no solar energetic particle events were observed. The particle enhancements are fewer in number and less intense at higher (approx 20 deg.) heliolatitudes. However, the similar spectral shapes of the accelerated particles at the two spacecraft indicate that the acceleration process is the same at the two latitudes, but less intense at the higher latitude.

Gold, R. E.↗
NASA NTRS1984

Exploring beyond the planets - The Pioneer 10 and 11 missions

The Pioneer 10 and 11 missions are surveyed and illustrated with drawings, maps, graphs, and diagrams, with an emphasis on their present exploration of the outer heliosphere. The main goals of this exploration are examined (search for the heliospheric boundary, measurement of galactic cosmic radiation, and search for a trans-Neptunian planet); the ten scientific instruments carried by each spacecraft are characterized; and the results obtained so far with regard to the solar wind and interplanetary magnetic field, cosmic rays, and asteroid belt, Jupiter, and Saturn are summarized.

Dyal, P.↗
NASA NTRS1983

Radial gradients of galactic cosmic rays measured by Pioneer 10 from 1-29 AU through the period of solar maximum

During the approach to maximum solar modulation in 1982, the radial gradient of high energy galactic cosmic rays gradually increased to about 2.5 percent/AU from the solar minimum value of about 1.5 percent/AU. In the same period, at energies lower than 70 MeV/n, the radial gradients for protons decreased from about 8 percent/AU to about 1 percent/AU. It is found that at solar maximum, in contrast to solar minimum, essentially all of the modulation of low energy cosmic rays occurs outside R = 29 AU. The combined effects of solar flare shocks coalescing in the far outer heliosphere may account for this dramatic change in the radial dependence of modulation.

Mckibben, R. B.↗
NASA NTRS1985

Evolution and interaction of large interplanetary streams

A computer simulation for the evolution and interaction of large interplanetary streams based on multi-spacecraft observations and an unsteady, one-dimensional MHD model is presented. Two events, each observed by two or more spacecraft separated by a distance of the order of 10 AU, were studied. The first simulation is based on the plasma and magnetic field observations made by two radially-aligned spacecraft. The second simulation is based on an event observed first by Helios-1 in May 1980 near 0.6 AU and later by Voyager-1 in June 1980 at 8.1 AU. These examples show that the dynamical evolution of large-scale solar wind structures is dominated by the shock process, including the formation, collision, and merging of shocks. The interaction of shocks with stream structures also causes a drastic decrease in the amplitude of the solar wind speed variation with increasing heliocentric distance, and as a result of interactions there is a large variation of shock-strengths and shock-speeds. The simulation results shed light on the interpretation for the interaction and evolution of large interplanetary streams. Observations were made along a few limited trajectories, but simulation results can supplement these by providing the detailed evolution process for large-scale solar wind structures in the vast region not directly observed. The use of a quantitative nonlinear simulation model including shock merging process is crucial in the interpretation of data obtained in the outer heliosphere.

Whang, Y. C.↗
NASA NTRS1986

Interaction of the solar wind with interstellar neutral hydrogen - Three-fluid model

It is commonly assumed in models of the solar wind-interstellar neutral hydrogen interaction that the ionized interstellar particles are quickly assimilated into the solar wind proton population and 'become indistinguishable' from the original solar wind. This assumption leads to the prediction that the solar wind proton temperature should increase with radius in the outer heliosphere. This temperature increase has not been observed. It is pointed out that assimilation of the interstellar particles to the point of indistinguishability takes place on the very long Coulomb collision time scale, and is not expected to occur within the heliosphere. Results are presented of a three-fluid model of the solar wind which consists of comoving thermal populations of protons of solar origin, protons produced by ionization of interstellar hydrogen, and electrons. The steady-state results yield a solar wind with a 'core' proton distribution which cools adiabatically, and a 'halo' of interstellar pickup protons which is maintained near 10 to the 7th K by the energy input of continued ionization and pickup. Such a distribution will not be observed to manifest the temperature increase at large heliocentric distances which is predicted from a one-fluid analysis. Further time-dependent calculations show a strong correlation between the densities of the solar wind and the interstellar pickup protons. It is suggested that the interstellar pickup population may be observable by the Voyager plasma instruments in low resolution mode during periods of high solar wind density and low solar wind temperature.

Isenberg, P. A.↗
NASA NTRS1987

Evolution of interstellar pickup ions in the solar wind

A model is constructed for the evolution of an interstellar pickup ion distribution in the solar wind. The model assumes that the ions are immediately isotropized at ionization and follows the subsequent development of the distribution function as the particles are convected with the solar wind. The effects of energy diffusion in an ambient wave field with a power law spectrum, adiabatic deceleration in the expanding solar wind, and continual addition of newly ionized particles are all included in the model. An analytical expression describing the evolution of the distribution function in phase space velocity and heliocentric radius is obtained. The distribution quickly approaches an asymptotic shape in phase space which depends on the relative efficiency of the energy diffusion process compared to that of adiabatic deceleration. At large distances from the sun the density of pickup ions falls as 1/r in this model. An expression for the distribution function at large distances and for large particle speed is presented. The asymptotic shape should describe the distribution of pickup ions in the outer heliosphere and could be used as an input distribution for a model of the anomalous component of heliosphere and could be used as an input distribution for a model of the anomalous component of cosmic rays. Comparison of this work with the recent observation of He(+) at 1 AU implies that the energy diffusion process is very weak inside 1 AU.

Isenberg, Philip A.↗
NASA NTRS1987

Solar wind stream structure at large heliocentric distances Pioneer observations

Time profiles and histograms of plasma data from Pioneers 10 and 11 are examined for the period between 1975 and 1983. During this time, Pioneer 10 traveled between a heliocentric distance of 8.7 and 30.4 AU. The velocity structure of the solar wind at these heliocentric distances is found to have one of two distinct forms: approximately 70 percent of the time the solar wind has a nearly flat velocity profile. Occasionally, this flat velocity profile is accompanied by quasi-periodic variations in density and in thermal speed consistent with the concept that the 'corotating interaction regions' which are produced by the interaction of high- and low-speed streams at intermediate heliocentric distances are replaced by 'pressure regions' in the outer heliosphere. The remaining 30 percent of the time the solar wind is marked by large (50-200 km/s) long-term (30-120 days) shifts in the average solar wind velocity.

Gazis, P. R.↗
NASA NTRS1988

The charge state of the anomalous cosmic-ray component

H, He, and O cosmic-ray energy spectra obtained in the outer heliosphere by the Voyager 2 and Pioneer 10 spacecraft during the most recent periods of declining solar activity are presented graphically and analyzed. The recovery of high-rigidity particles is shown to be significantly delayed relative to that of the low-rigidity particles. This finding and the demodulated source spectra are attributed to the presence of singly ionized anomalous He and O, as predicted by Fisk et al. (1974).

Mcdonald, F. B.↗
NASA NTRS1989

Electron heat flux dropouts in the solar wind - Evidence for interplanetary magnetic field reconnection?

An examination of ISEE-3 data from 1978 reveal 25 electron heat flux dropout events ranging in duration from 20 min to over 11 hours. The heat flux dropouts are found to occur in association with high plasma densities, low plasma velocities, low ion and electron temperatures, and low magnetic field magnitudes. It is suggested that the heat flux dropout intervals may indicate that the spacecraft is sampling plasma regimes which are magnetically disconnected from the sun and instead are connected to the outer heliosphere at both ends.

Mccomas, D. J.↗
NASA NTRS1989

Remote sensing of the termination of the solar wind via in situ plasma measurements

Since 1983 the Plasma Wave experiments on the two Voyager spacecraft have detected low frequency radio noise in the outer heliosphere which has been postulated to emanate from the terminal shock of the solar wind or, possibly, from the heliopause itself. The solar wind data from the Plasma Science experiment on the Voyager spacecraft are studied to search for correlations with these radio emissions. It is found that two anomalous high speed streams passed Voyager 2 in late 1982 and early 1983 and it is suggested that the interaction of the streams with the heliospheric terminal shock is responsible for the generation of the most intense radio noise observed later in the same year. If the stream speeds did not decrease in traveling to the interaction region, that region is about 135 AU from the sun. This is consistent with previous estimates of the distance to the inner heliospheric shock.

Mcnutt, R. L., Jr.↗
NASA NTRS1990

Simulation of period doubling of recurrent solar wind structures

Based on satellite observations of a recurrent solar wind structure conducted in 1974, an MHD simulation model, and input functions generated from plasma and magnetic field data, the continuing evolution of the solar wind structure outside 5 AU is studied. The model uses the Rankine-Hugoniot relations to describe the jumps in flow properties across the shocks, and it treats shocks as surfaces of discontinuity with zero thickness. Two interaction processes (the collision and the merging of shocks) play important roles in restructuring the solar wind in the outer heliosphere. The simulation result shows that period doubling occurs between 5 and 10 AU. The recurrent solar wind appears to be a persistent new structure between 10 and 20 AU, and it consists of one merged interaction region per solar rotation.

Whang, Y. C.↗
NASA NTRS1991

Cosmic ray modulation - Voyager 2 observations, 1987-1988

The intensity profile of cosmic rays above 70 MeV observed by Voyager 2 and its relation to the interplanetary magnetic field and plasma at the beginning of the new modulation cycle from day 190, 1987 to day 345, 1988 in the region from 23.3 AU to 27.8 AU is analyzed. The cosmic ray intensity profile was approximately a series of four plateaus separated by three steps in which the intensity dropped abruptly. Each step was associated with a region in which the magnetic field, density and temperature were higher than average. The plateaus were associated with regions in which the magnetic field was alternately strong and weak. The solar wind within 200 AU during this interval can be roughly pictured as consisting of three shells between which the flow was quasiperiodic with a 26 day periodicity. The latitudinal extent of the shells in the northern hemisphere was probably less than 33 deg, since no steps were observed by Voyager 1. Drift motions might play a role during the recovery phase, just prior to the onset of the new modulation cycle, in the plateau regions between the shells, within the shells where drifts in various directions might mimic diffusion, and close to 1 AU, where large regions of intense magnetic fields have not yet formed. However the principal decreases in the cosmic ray intensity in the outer heliosphere during 1987 and 1988 were associated with the passage of broad regions of intense magnetic fields, consistent with the diffusion/convection model.

Burlaga, L. F.↗