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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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NASA NTRS1983

Solar flare neutron fluxes derived from interplanetary charged particle measurements

The first observation of interplanetary protons produced by the decay of solar neutrons made by Evenson et al. (1983) after a solar flare which occurred on June 3, 1982, is expanded, extending the measurement of the spectrum of the decay protons to higher energy. The spectrum of the decay protons for the June 21, 1980, neutron event observed by Chupp et al. (1982) is also determined. The measurements suggest that neutron emission from solar flares is isotropic and that different flares emit neutrons with similar spectra. The importance of such measurements in the study of interplanetary propagation of charged particles is discussed.

Evenson, P.↗
NASA NTRS1986

Study of Travelling Interplanetary Phenomena (STIP) workshop travel

Thirty six abstracts are provided from the SCOSTEP/STIP Symposium on Retrospective Analyses and Future Coordinated Intervals held in Switzerland on June 10 to 12, 1985. Six American scientists participated in the symposium and their abstracts are also included. The titles of their papers are: (1) An analysis of near surface and coronal activity during STIP interval 12, by T. E. Gergely; (2) Helios images of STIP intervals 6, B. V. Jackson; (3) Results from the analysis of solar and interplanetary observations during STIP interval 7, S. R. Kane; (4) STIP interval 19, E. Cliver; (5) Hydrodynamic buoyancy force in the solar atmosphere, T. Yeh; and (6) A combined MHD modes for the energy and momentum transport from solar surface to interplanetary space, S. T. Wu.

Wu, S. T.↗
NASA NTRS1986

Laboratory studies of interplanetary dust

Interplanetary dust particles (IDPs) are a form of primitive extraterrestrial material. In spite of the formidable experimental problems in working with particles that are too small to be seen with the naked eye, it has proven possible to obtain considerable information concerning their properties and possible origins. Dust particles collected in the stratosphere were reviewed. These particles are the best available samples of interplanetary dust and were studied using a variety of analytical techniques.

Walker, R. M.↗
NASA NTRS1986

Preparation, analysis and release of simulated interplanetary grains into low Earth orbit

Astronomical observations which reflect the optical and dynamical properties of interstellar and interplanetary grains are the primary means of identifying the shape, size, and the chemistry of extraterrestrial grain materials. Except for recent samplings of extraterrestrial particles in near-Earth orbit and in the stratosphere observations were the only method of deducing the properties of extraterrestrial particles. In order to elucidate the detailed characteristics of observed dust, the observations must be compared with theoretical studies, some of which are discussed in this volume, or compared with terrestrial laboratory experiments. The formation and optical characterization of simulated interstellar and interplanetary dust with particular emphasis on studying the properties on irregularly shaped particles were discussed. Efforts to develop the techniques to allow dust experiments to be carried out in low-Earth orbit were discussed, thus extending the conditions under which dust experiments may be performed.

Stephens, J. R.↗
NASA NTRS1985

Evidence of scattering effects on the sizes of interplanetary Type III radio bursts

An analysis is conducted of 162 interplanetary Type III radio bursts; some of these bursts have been observed in association with fast electrons and Langmuir wave events at 1 AU and, in addition, have been subjected to in situ plasma parameter measurements. It is noted that the sizes of burst sources are anomalously large, compared to what one would anticipate on the basis of the interplanetary plasma density distribution, and that the variation of source size with frequency, when compared with the plasma frequency variation measured in situ, implies that the source sizes expand with decreasing frequency to fill a cone whose apex is at the sun. It is also found that some local phenomenon near the earth controls the apparent size of low frequency Type III sources.

Steinberg, J. L.↗
NASA NTRS1986

An interplanetary magnetic field ensemble at 1 AU

A method for calculation ensemble averages from magnetic field data is described. A data set comprising approximately 16 months of nearly continuous ISEE-3 magnetic field data is used in this study. Individual subintervals of this data, ranging from 15 hours to 15.6 days comprise the ensemble. The sole condition for including each subinterval in the averages is the degree to shich it represents a weakly time-stationary process. Averages obtained by this method are appropriate for a turbulence description of the interplanetary medium. The ensemble average correlation length obtained from all subintervals is found to be 4.9 x 10 to the 11th cm. The average value of the variances of the magnetic field components are in the approximate ratio 8:9:10, where the third component is the local mean field direction. The correlation lengths and variances are found to have a systematic variation with subinterval duration, reflecting the important role of low-frequency fluctuations in the interplanetary medium.

Matthaeus, W. H.↗
NASA NTRS1985

Acceleration of interplanetary solar electrons in the 1982 August 14 flare

The solar flare on August 14, 1982 (about 0507 UT) produced hard X-rays, gamma-rays, and an electron-rich interplanetary particle event. Because of its location (N11, W61), the flare site was magnetically well connected to the ISEE 3 spacecraft. The ISEE 3 observations have provided a detailed time history of 15 keV-1.9 MeV photon emission from the flare and the relativistic (greater than 3 MeV) solar electrons in interplanetary space. These observations indicate that a significant fraction of the relativistic electrons escaping from the sun were accelerated during the impulsive phase simultaneously with the energetic electrons producing the hard X-ray and gamma-ray continuum at the sun.

Kane, S. R.↗
NASA NTRS1986

On ion acceleration in interplanetary quasi-perpendicular shock waves

The kinematic and pitch angle scattering constraints for multiple shock encounters to occur are investigated. The results suggest that (1) large particle anisotropies and a large number of shock encounters are not mutually exclusive and (2) solar wind ions are not directly injected into the nearly perpendicular interplanetary shock acceleration process. Also, the average number of shock encounters required to accelerate an ion between two energies is calculated. The results are consistent with the shock geometry dependence observed in interplanetary shock spike and corotating interaction region associated energetic ion events.

Pesses, M. E.↗
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 NTRS1987

Studies of the interplanetary magnetic field: IMP's to Voyager

During the last two decades, spacecraft projects and individual experiments for which Frank McDonald was a leader have contributed very significantly to the current understanding of the structure of interplanetary space and the correlation between solar and interplanetary disturbances. Studies on the IMP, HELIOS, and Pioneer spin-stabilized spacecraft and the larger attitude-stabilized Voyager spacecraft have provided data sets from which the modern view of the heliosphere has evolved. That concept in which the inner solar system is shown to be dominated by individual streams associated with specific source regions on the Sun is illustrated. As these high-speed streams overtake the preexisting solar plasma, they coalesce and modify the characteristics so that at larger heliocentric distances, these disturbances appear as radially propagating concentric shells of compressed magnetic fields and enhanced fluctuations

Ness, Norman F.↗
NASA NTRS1986

Modeling of ion acceleration through drift and diffusion at interplanetary shocks

A test particle simulation designed to model ion acceleration through drift and diffusion at interplanetary shocks is described. The technique consists of integrating along exact particle orbits in a system where the angle between the shock normal and mean upstream magnetic field, the level of magnetic fluctuations, and the energy of injected particles can assume a range of values. The technique makes it possible to study time-dependent shock acceleration under conditions not amenable to analytical techniques. To illustrate the capability of the numerical model, proton acceleration was considered under conditions appropriate for interplanetary shocks at 1 AU, including large-amplitude transverse magnetic fluctuations derived from power spectra of both ambient and shock-associated MHD waves.

Decker, R. B.↗
NASA NTRS1987

Field line draping about fast coronal mass ejecta - A source of strong out-of-the-ecliptic interplanetary magnetic fields

Fast coronal mass ejecta interact strongly with the ambient interplanetary plasma and magnetic field into which they propagate. A shock forms in front of an ejection, and the slower moving ambient plasma ahead is accelerated and deflected from its path. It is argued that such flow accelerations and deflections of the ambient plasma must produce a draping of the ambient interplanetary magnetic field about the ejected material similar to that which occurs in the magnetosheath surrounding the earth's magnetosphere. The draping pattern should depend upon the overall size and shape of the ejection, its speed relative to the ambient plasma ahead, the orientation of the ambient magnetic field, and the position where the shocked plasma is sampled. At some locations upstream from an ejection draping leads to an enhancement of the out-of-the-ecliptic field component B(Z) at the expense of the ecliptic components. It is suggested that draping plays an important role in producing intervals of strong and prolonged negative B(Z) in the ecliptic plane at 1 AU, and thus may be an important factor in stimulating geomagnetic activity.

Gosling, J. T.↗
NASA NTRS1987

The cause of high-intensity long-duration continuous AE activity (HILDCAAS) - Interplanetary Alfven wave trains

It is shown that high intensity (AE of greater than 1,000 nT), long duration (T of greater than 2d) continuous auroral activity events are caused by outward (from the sun) propagating interplanetary Alfven wave trains. The Alfven waves are often (but not always) detected several days after major interplanetary events, such as shocks and solar wind density enhancements. Presumably, magnetic reconnection between the southward components of the Alfven wave magnetic fields and magnetospheric fields is the mechanism for transfer of solar wind energy to the magnetosphere.

Tsurutani, Bruce T.↗
NASA NTRS1987

Interplanetary radial cosmic-ray gradients and their implication for a possible large modulation effect at the heliospheric boundary

It is proposed here that a large and time-variable part of the overall 11-year cosmic ray modulation in the heliosphere takes place near the heliosphere boundary itself. This conclusion is reached by examining interplanetary radial gradient measurements which show that out to 30-40 AU this gradient remains nearly independent of heliocentric distance throughout the solar cycle. Properties of the solar wind which suggest that the distance to the pressure balance boundary does not vary by more than + or - 25 percent over the solar cycle are also used in support of the proposal. The importance of the large modulation effect at the boundary could exceed that of interplanetary effects expected from present models.

Webber, W. R.↗
NASA NTRS1987

Energetic interplanetary shocks, radio emission, and coronal mass ejections

The interplanetary shocks which generate detectable low-frequency radio emission, represent as a group, the most energetic shocks produced by the sun. For all interplanetary (IP) shocks which generated so-called IP type II events, the associated solar events involved fast coronal mass ejections (CMEs). In comparison with the set of all CMEs detected by the Solwind coronagraph, the CMEs associated with IP type II events are the most massive and energetic. The majority belong to the structural classes described by the Solwind researchers as 'curved front' or 'halo'.

Cane, H. V.↗
NASA NTRS1987

Change in interplanetary shock acceleration preceding STIP Interval 17

The intensity and frequency of shock acceleration events in the interplanetary medium decreased dramatically in early 1985. Low energy ions were observed by IMP 8 at 1 AU and Voyagers 1 and 2 at 22 and 16 AU, respectively. Voyager 1 was at 25 deg heliographic latitude while IMP 8 and Voyager 2 were near the solar equatorial plane. The decrease in low energy shock events led to a drop in the average ion flux by a factor of 20 to 50. It started about day 10 of 1985 in the approximately .5 MeV channel on IMP8 and took approximately 75 days to reach the new, lower, background level. The decrease at the Voyagers started approximately 50 days later. The time delay between the start of the decrease at IMP and at Voyager 2 implies that decrease was convected outward with a velocity of approximately 535 km/sec. The intensity and frequency of interplanetary shock events remained at the lower level for at least 1.5 years.

Gold, R. E.↗
NASA NTRS1987

Dynamics of magnetic clouds in interplanetary space

Magnetic clouds observed in interplanetary space may be regarded as extraneous bodies immersed in the magnetized medium of the solar wind. The interface between a magnetic cloud and its surrounding medium separates the internal and external magnetic fields. Polarization currents are induced in the peripheral layer to make the ambient magnetic field tangential. The motion of a magnetic cloud through the interplanetary medium may be partitioned into a translational motion of the magnetic cloud as a whole and an expansive motion of the volume relative to the axis of the magnetic cloud. The translational motion is determined by two kinds of forces, i.e., the gravitational force exerted by the Sun, and the hydromagnetic buoyancy force exerted by the surrounding medium. On the other hand, the expansive motion is determined by the pressure gradient sustaining the gross difference between the internal and external pressures and by the self-induced magnetic force that results from the interaction among the internal currents. The force resulting from the internal and external currents is a part of the hydromagnetic buoyancy force, manifested by a thermal stress caused by the inhomogeneity of the ambient magnetic pressure.

Yeh, Tyan↗
NASA NTRS1987

Plasma-tail activity and the interplanetary medium at Halley's Comet during Armada Week: 6-14 March 1986

The encounters of five spacecraft with Halley's Comet during 6-14 March 1986 offered a unique opportunity to calibrate the solar-wind interaction with cometary plasmas as recorded by remote wide-field and narrow-field/narrowband imaging. Perhaps not generally recognized in the comet community is the additional opportunity offered by the Halley Armada to study the structure of the solar-wind and interplanetary magnetic field (IMF) in three dimensions using five sets of data obtained over similar time intervals and heliocentric distances, but at somewhat different heliolatitudes. In fact, the two problems, i.e., comet physics and the structure of the interplanetary medium, are coupled if one wants to understand what conditions pertained at the comet between the encounters. This relationship is discussed.

Niedner, Malcolm B., Jr.↗