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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Variations in plasma wave intensity with distance along the electron foreshock boundary at Venus

Plasma waves are observed in the solar wind upstream of the Venus bow shock by the Pioneer Venus Orbiter. These wave signatures occur during periods when the interplanetary magnetic field through the spacecraft position intersects the bow shock, thereby placing the spacecraft in the foreshock region. Wave intensity is analyzed as a function of distance along the electron foreshock boundary. It is found that the peak wave intensity may increase along the foreshock boundary from the tangent point to a maximum value at several Venus radii, then decrease in intensity with subsequent increase in distance. These observations could be associated with the instability process: the instability of the distribution function increasing with distance from the tangent point to saturation at the peak. Thermalization of the beam for distances beyond this point could reduce the distribution function instability resulting in weaker wave signatures.

Crawford, G. K.↗
NASA NTRS1990

Modeling of a series of interplanetary disturbance events in September 1978

A series of three interplanetary disturbance events in September 1978 are modeled. Flares responsible for the three shock waves are tentatively identified. It is shown that the computed interplanetary scintillation (IPS) sky maps for flares on September 21 and 23 clearly show that the September 21 flare was responsible for the IPS event and the geomagnetic storms which were observed on September 24-25, although it has been generally believed that a flare on September 23 was their origin. Thus, this is a good example to show the usefulness of IPS observations to identify the responsible solar event and predict the arrival of the shock wave. It is also shown that the IPS event was not caused by a high speed stream from a coronal hole.

Akasofu, S.-I.↗
NASA NTRS1979

Electrostatic noise at the plasma frequency beyond the earth's bow shock

Scarf et al. (1971) and Dunckel (1974) have shown that there are, very frequently, intense electrostatic waves whose frequency is near the plasma frequency upstream of the earth's bow shock and that these waves are correlated with the presence of energetic electrons from the bow shock. Also, Fredericks et al. (1971) have postulated a two-stream instability. The paper investigates these phenomena further, by comparing electrostatic noise at or near the ambient solar wind plasma frequency with times when the interplanetary magnetic field probably connects to the shock. Evidence is presented that Scarf et al. and Fredericks et al. were correct in their explanation of the phenomenon, and that the double-humped distribution would be expected only in a region too small to be resolved by the plasma measurements made so far.

Filbert, P. C.↗
NASA NTRS1980

Energetic particles in space

A review is presented of observations of suprathermal particles in the interplanetary medium along with new data on low energy particles from experiments aboard the ISEE spacecraft. Energy spectra of protons in the near earth atmosphere are plotted in the rest frame of the solar wind noting that at energies above 10 to the 9th eV, the galactic cosmic ray electron component has an unattenuated access into the heliosphere. Solar transient events such as flares accelerate and release energetic particles into the interplanetary medium; flare particle fluxes generate shock waves propagating past 1 AU following the event. It is concluded that the energy spectra for shock wave accelerations show a characteristic shape in accordance with the power law with a rapid steepening at high energies.

Lin, R. P.↗
NASA NTRS1982

Starprobe - The science opportunities

The scientific objectives of the NASA Starprobe mission for an unmanned spacecraft to pass within three solar radii of the sun's surface are reviewed. Fundamental observations of gravitation, relativity, and factors related to the solar interior, measurements of the static and dynamic electromagnetic fields and the particle populations close to the sun, and observations of the solar atmosphere from the photosphere to the corona with high spatial resolution would be possible with the Starprobe. A determination of the quadrupole coefficient in the expansion of the gravitational potential field of the sun is noted to be possible by measuring the departure from a Keplerian orbit of the Starprobe as it passes perihelion, yielding data on the rate of revolution of the interior of the sun. Further information on shock acceleration, energy losses, radio bursts, interplanetary propagation, and diffusion will be available at 10-60 solar radii.

Underwood, J. H.↗
NASA NTRS1984

Power spectral signatures of interplanetary corotating and transient flows

Studies of the time behavior of the galactic cosmic ray intensity have concluded that long term decreases in the intensity are generally associated with systems of interplanetary flows that contain flare generated shock waves, magnetic clouds and other transient phenomena. The magnetic field power spectral signatures of such flow systems are compared to power spectra obtained during times when the solar wind is dominated by stable corotating streams that do not usually produce long-lived reduction in the cosmic ray intensity. The spectral signatures of these two types of regimes (transient and corotating) are distinct. However, the distinguishing features are not the same throughout the heliosphere. In data collected beyond 1 AU the primary differences are in the power spectra of the magnitude of the magnetic field rather than in the power in the field components. Consequently, decreases in cosmic ray intensity are very likely due to magnetic mirror forces and gradient drifts rather than to small angle scattering due to cyclotron wave-particle interactions.

Goldstein, M. L.↗
NASA NTRS1984

Power spectral signatures of interplanetary corotating and transient flows

Studies of the time behavior of the galactic cosmic ray intensity have concluded that long term decreases in the intensity are generally associated with systems of interplanetary flows that contain flare generated shock waves, magnetic clouds and other transient phenomena. The magnetic field power spectral signatures of such flow systems are compared to power spectra obtained during times when the solar wind is dominated by stable corotating streams that do not usually produce long-lived reduction in the cosmic ray intensity. The spectral signatures of these two types of regimes (transient and corotating) are distinct. However, the distinguishing features are not the same throughout the heliosphere. In data collected beyond 1 AU the primary differences are in the power spectra of the magnitude of the magnetic field rather than in the power in the field components. Consequently, decreases in cosmic ray intensity are very likely due to magnetic mirror forces and gradient drifts rather than to small angle scattering due to cyclotron wave-particle interactions. Previously announced in STAR as N84-18131

Goldstein, M. L.↗
NASA NTRS1985

Influence of magnetic clouds on cosmic ray intensity variations

Neutron monitor data has been analyzed to study the nature of galactic cosmic ray transient modulation associated with three types of interplanetary magnetic clouds - clouds associated with shocks, stream interfaces and cold magnetic enhancements.

BADRUDDIN↗
NASA NTRS1988

Earth rocks on Mars: Must planetary quarantine be rethought

Recent geochemical, isotopic, and rare gas studies suggest that eight SNC meteorites originated on the planet Mars. Since Martian rocks are found on Earth, consideration is being given to finding Earth rocks on Mars. Detailed consideration of the mechanism by which these meteorites were lofted into space strongly suggest that the process of stress-wave spallation near a large impact with, perhaps, an assist from vapor plume expansion, is the fundamental process by which lightly-shocked rock debris is ejected into interplanetary space. The theory of spall ejection was used to examine the mass and velocity of material ejected from the near vicinity of an impact. It seems likely that the half-dozen largest impact events on Earth would have ejected considerable masses of near surface rocks into interplanetary space. No computations were performed to indicate how long Earth ejecta would take to reach Mars.

Melosh, H. J.↗
NASA NTRS1994

Magnetosheath magnetic field variability

A case study using simulations IRM and CCE observations demonstrates that transient magnetospheric events correspond to pressure pulses in the magnetosheath, inward bow shock motion, and magnetopause compression. Statistical surveys indicate that the magnetosheath magnetic field orientation rarely remains constant during periods of magnetopause and bow shock motion (both characterized by periods of 1 to 10 min). There is no tendency for bow shock motion to occur for southward interplanetary magnetic field (IMF) orientations.

Sibeck, D. G.↗
NASA NTRS2018

Magnetospheric Multiscale Observations of Turbulent Magnetic and Electron Velocity Fluctuations in Earth's Magnetosheath Downstream of a Quasi-Parallel Bow Shock

We present statistical single-spacecraft observations of magnetic and electron velocity fluctuations in Earth's magnetosheath, likely in the vicinity of the magnetopause, downstream of a bow shock immersed in quasi-parallel interplanetary magnetic field conditions, a situation conducive to plasma turbulence in the downstream flow. These fluctuations exhibit scale-dependent behavior, wherein histograms of their Partial Variance of Increments (PVIB or PVIV(sub e)) demonstrate highly non-Gaussian forms at small scales and are reasonably well-described by kappa distributions, albeit with fitted values of the kappa parameter only slightly larger than 1.5, exemplifying their power law nature at large values of PVI. At larger scales, the PVI histograms lose their non-Gaussian nature and are well described by both Gaussian and kappa distributions with large values of the kappa parameter. The PVI histograms furthermore exhibit kurtosis that increases with decreasing scale, a characteristic that is much more prominent in the magnetic fluctuations than in the electron velocity fluctuations. This feature that is not yet explained. In both cases, the results are characteristic of turbulent intermittency.

Pollock, C. J.↗
NASA NTRSDate not supplied

Inner Magnetospheric Physics

A brief overview of inner magnetospheric physics will be given. As a discipline, magnetospheric physics is a young science. Its earliest experimental beginnings were in the 1950s with the study of low frequency radio waves originating from lightning and later with the first orbiting satellite, Explorer 1. The solar wind drives the coupled magnetospheric system from the ionosphere-thermosphere, plasmasphere, ring current, radiation belts, out through the region of interface to interplanetary space, the magnetosheath and bow shock. The basic plasma systems, their motions, and responses to the driving solar wind will be mentioned. These highlights of the magnetospheric system are intended only to provide points of reference for further more in-depth study.

inner magnetosphere, physical processes↗
NASA NTRS1983

Dependence of 50-keV upstream ion events at IMP 7 and 8 upon magnetic field bow shock geometry

Results are presented for a statistical study of four years (1972-1976) of IMP 7 and 8 observations at approximately 40 R(E) of 50-200 keV upstream ion events measured with the Energetic Particle Experiment. A monotonic increase in the probability of observing upstream particle events is found with a decrease in the angle (theta-Bn) between the interplanetary magnetic field (IMF) and the local shock normal at the point where the IMF intersects the bow shock, independent of the length of time of bow shock connections exceeding approximately 10 min. Approximately equal probabilities are found for observing an event above a given flux from any portion of the bow shock with the same value of theta-Bn, a growth time of the 50-200 keV events of approximately 10 min, a maximum attainable flux of approximately 25,000/sq cm s sr, and a positive correlation between the probability of exceeding a given flux and the 3 hr Kp index. It is concluded that the local structure of the bow shock in the immediate vicinity of the field line connection is the dominant influence in the generation process of energetic upstream particle events and that wave-particle interactions produce a self-throttling mechanism that limits the maximum flux of ions escaping the upstream foreshock.

Mitchell, D. G.↗
NASA NTRS1974

Magnetic field observations near Venus - Preliminary results from Mariner 10

The NASA-GSFC magnetic field experiment on Mariner 10 is the first flight of a dual magnetometer system conceived to permit accurate measurements of weak magnetic fields in space in the presence of a significant and variable spacecraft magnetic field. Results from a preliminary analysis of a limited data set are summarized in this report, which is restricted primarily to Venus encounter. A detached bow shock wave that develops as the super Alfvenic solar wind interacts with the Venusian atmosphere has been observed. However, the unique coincidence of trajectory position and interplanetary field orientation at the time of bow shock crossing led to a very disturbed shock profile with considerably enhanced upstream magnetic fluctuations. At present it is not possible to ascertain the nature and characteristics of the obstacle responsible for deflecting the solar wind flow. Far downstream disturbances associated with the solar wind wake have been observed.

Ness, N. F.↗
NASA NTRS1984

A kinky heliospheric current sheet - Cause of CDAW-6 substorms

Two magnetospheric substorms and the intensification of the second are caused by interplanetary magnetic field and ram pressure changes associated with a kinky heliospheric current sheet (KHCS). The responsible interplanetary features occur in a highly compressed region between a solar flare-associated shock wave and the cold driver gas. The possibility that the interplanetary structure is a 'magnetic cloud' is ruled out.

Tsurutani, B. T.↗
NASA NTRS1981

Measurements of bow shock particles far upstream from the earth

Electrons and ions moving upstream frequently appear at distances up to 240 earth radii from earth at times when the direction of the interplanetary magnetic field allows their propagation from the bow shock. Strong asymmetries in the ion angular pitch angle distribution are often observed, a consequence of the sharp gradient in guiding center density and very weak scattering. The gradient is due to the restricted spatial region over which these particles are accelerated. The solar wind electric field acts on these particles and produces striking effects in both the ion angular distributions and the ion energy spectra. The frequent occurrence of these effects implies that the source region of the diffuse ions at the bow shock is not more than a few tens of thousands of km.

Anderson, K. A.↗