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At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

A reverse shock associated with a stream-stream interaction - The February 29, 1968, event

A clearly defined perpendicular fast reverse shock was found in the interplanetary plasma and magnetic field data from Explorer 33 and 35. A Pioneer 8 observation, which is not unambiguously identifiable because of insufficient data, indicates the evolution of this event. It is suggested that this reverse shock was formed from a stream-stream interaction and that an associated forward shock was developing and probably formed beyond the earth's orbit.

Chao, J. K.↗
NASA NTRS1986

Interplanetary magnetic field control of the Venus magnetosheath field and bow shock location

Six Venus years of Pioneer Venus Orbiter (PVO) data are analyzed in a coordinate system which isolates magnetic effects. The field draping pattern features two lobes easily identifiable even in the near planet region. The magnetosheath magnetic magnitude has a hemispherical asymmetry controlled by the IMF orientation in a manner suggesting preferrential ion pickup in one hemisphere. This result complements recent findings that the bow shock position is responsive to IMF direction. Examination of the ionopause position to evaluate ionospheric effects on the overall asymmetry of thfe Venus-solar wind interaction produces negative but not conclusive results.

Phillips, J. L.↗
NASA NTRS1973

A reverse shock associated with a stream-stream interaction: The 29th February 1968 event

A clearly defined perpendicular fast reverse shock was found in the interplanetary plasma and magnetic field data from Explorers 33 and 35. An observation by Pioneer 8, which is not unambiguously identifiable because of insufficient data, indicates the evolution of this event. It is suggested that this reverse shock was formed from a stream-stream interaction and that an associated foward shock was developing and probably formed beyond the earth's orbit.

Chao, J. K.↗
NASA NTRS1986

Shock acceleration of nucleons at 16 deg and above solar latitude associated with interplanetary corotating interaction regions

The analysis of magnetic field and nuclei measurements in the 1 to 10 MeV/nucleon range for protons and helium at about 16 deg N solar latitude near solar cycle minimum (1975-76) shows both: (1) that nucleons are accelerated locally in corotating shocks, and (2) that the associated recurring corotating interaction regions (CIRs) at about 16 deg latitude have approximately the same temporal and spatial parameters found for CIRs in the equatorial plane at radial distances less than 5 AU. The evidence indicates that both the CIR structures and nucleon acceleration by shocks extend to intermediate solar latitudes and are likely to be observed during the Ulysses Mission out of the ecliptic plane.

Simpson, J. A.↗
NASA NTRS1989

The magnetospheric response to 8-minute period strong-amplitude upstream pressure variations

This paper documents a series of brief, strong (delta p/p = 1), dynamic pressure oscillations that occurred in the region upstream of the earth's bow shock during a period of radial interplanetary magnetic field. The analyzed set of oscillations, which may be either intrinsic solar wind or bow shock-related phenomena, recur approximately every 8-10 min, and their magnetic field signatures occur nearly simultaneously over great distances transverse to the earth-sun line. The pressure oscillations appear to drive tailward-moving magnetopause surface wavelets. In turn, the surface wavelets can be identified as hydromagnetic waves with strong compressional components in the outer magnetosphere and as quasi-periodic variations in electron precipitation and high-latitude ground pulsations. Observations by spacecraft in the outer dayside magnetosphere are used to predict geosynchronous and subsolar magnetic field strengths, the location of the subsolar magnetopause, the solar wind dynamic pressure, and variations in the energetic magnetospheric ion flux.

Sibeck, D. G.↗
NASA NTRS2023

The Effect of the Ambient Solar Wind Medium on a CME-driven Shock and the Associated Gradual Solar Energetic Particle Event

We present simulation results of a gradual solar energetic particle (SEP) event detected on 2021 October 9 by multiple spacecraft, including BepiColombo (Bepi) and near-Earth spacecraft such as the Advanced Composition Explorer (ACE). A peculiarity of this event is that the presence of a high-speed stream (HSS) affected the low-energy ion component (≲5 MeV) of the gradual SEP event at both Bepi and ACE, despite the HSS having only a modest solar wind speed increase. Using the EUHFORIA (European Heliospheric FORecasting Information Asset) magnetohydrodynamic model, we replicate the solar wind during the event and the coronal mass ejection (CME) that generated it. We then combine these results with the energetic particle transport model PARADISE (PArticle Radiation Asset Directed at Interplanetary Space Exploration). We find that the structure of the CME-driven shock was affected by the nonuniform solar wind, especially near the HSS, resulting in a shock wave front with strong variations in its properties such as its compression ratio and obliquity. By scaling the emission of energetic particles from the shock to the solar wind compression at the shock, an excellent match between the PARADISE simulation and in situ measurements of ≲5 MeV ions is obtained. Our modeling shows that the intricate intensity variations observed at both ACE and Bepi were influenced by the nonuniform emission of energetic particles from the deformed shock wave and demonstrates the influence of even modest background solar wind structures on the development of SEP events.

Solar energetic particles↗
NASA NTRS1979

Pitch angle distributions of energetic protons near the earth's bow shock

Measurements of energetic protons between about 28 and about 145 keV on ISEE-1 upstream and downstream of the earth's bow shock during times of a radial interplanetary magnetic field are presented. The protons exhibited a slight antisunward flow in the spacecraft system in front of the bow shock and a strong flow along the magnetic field in the spacecraft system in the magnetosheath. Compton-Getting transformations of these anisotropies into the plasma frame of reference have been performed. It is argued that the observations can be explained best in terms of particle acceleration by multiple reflection between the bow shock and upstream scattering centers.

Scholer, M.↗
NASA NTRS1985

The Propagation of Solar Energetic Particles in Magnetic Channels

The existence of interplanetary flow systems produced by the entrainment of interplanetary transients, consisting of flare produced shocks, high speed solar wind streams and coronal mass ejection, has been established. This entrainment process produces enhanced regions of the interplanetary magnetic field that should be connected back to the solar corona. These compressed regions can provide a preferred magnetic channel for the propagation of solar cosmic rays. The characteristics of these events appear to be different from those previously reported by the NASA/University of New Hampshire team and the University of Chicago in their study of a large number of events in the region beyond 1 AU. These new events have a very flat energy spectra (with gamma = approx. 1.5) that frequently extend to energies above 100 MeV and have a significant enhancement of MeV electrons.

Mcdonald, F. B.↗
NASA NTRS1992

Endogenous production, exogenous delivery and impact-shock synthesis of organic molecules - An inventory for the origins of life

The contribution of organic-rich comets, carbonaceous asteroids, and interplanetary dust particles and of impact shock-synthesized organics in the atmosphere to the origin of life on earth is studied and quantitatively compared with the principal non-heavy-bombardment sources of prebiotic organics. The results suggest that heavy bombardment before 3.5 Gyr ago either produced or delivered quantities of organics comparable to those produced by other energy sources.

Chyba, Christopher↗
NASA NTRS1986

Coupled hydromagnetic wave excitation and ion acceleration upstream of the Jovian bow shock

We extend the Lee (1982) self-consistent theory of upstream wave excitation and particle energization to address observations by Voyager 2 of sunward propagating MHD waves and diffuse suprathermal particle populations upstream of the Jovian bow shock. Two new ideas are incorporated into the theory. First, the interplanetary seed wave population is taken to be an equal admixture of waves propagating both toward and away from the shock parallel to the interplanetary magnetic field. Second, finite connection times are incorporated approximately into the theory in an effort to understand whether the particle spectra at high energy are limited by particle escape or finite connection time. It is found that finite connection times dominate the particle distribution at energies above 40 keV. In this manner the suprathermal proton distributions can be accounted for by a multiple reflection, shock acceleration theory. We find that the theory can also account for the low-frequency waves observed upstream of the shock in conjunction with the suprathermal ions.

Smith, C. W.↗
NASA NTRS1984

Magnetohydrodynamic modelling of interplanetary disturbances between the sun and earth

A time-dependent, nonplanar, two-dimensional magnetohydrodynamic computer model is used to simulate a series, separately examined, of solar flare-generated shock waves and their subsequent disturbances in interplanetary space between the sun and the earth's magnetosphere. The 'canonical' or ansatz series of shock waves include initial velocities near the sun over the range 500 to 3500 km/s. The ambient solar wind, through which they propagate, is taken to be a steady state homogeneous plasma (that is, independent of heliolongitude) with a representative set of plasma and magnetic field parameters. Complete sets of solar wind plasma and magnetic field parameters are presented and discussed. Particular attention is addressed to the MHD model's ability to address fundamental operational questions vis-a-vis the long-range forecasting of geomagnetic disturbances. These questions are: (1) will a disturbance (such as the present canonical series of solar flare shock waves) produce a magnetospheric and ionospheric disturbance, and, if so, (2) when will it start, (3) how severe will it be, and (4) how long will it last? The model's output is used to compute various solar wind indices of current interest as a demonstration of the model's potential for providing 'answers' to these questions.

Dryer, M.↗
NASA NTRS1984

Characteristics of the magnetospheric source of interplanetary energetic particles

The Earth's bow shock is frequently cited as an example of an astrophysical shock where particle acceleration is observed. However, because energetic particles observed upstream of the bow shock may be accelerated within the magnetosphere, it is important to understand the properties of the magnetospheric source. A first order picture of the spatial distribution of magnetospheric particles in the magnetosheath and upstream is obtained by mapping those magnetic field lines which drape over the magnetopause through the bow shock. Subsets of these field lines that connect to potential sites of magnetic merging on the magnetopause are also traced in the event that leakage occurs preferentially where normal components of the field are present across the boundary. The results can be used to determine whether the so-called diffuse particles observed upstream are accelerated locally or within the magnetosphere.

Luhmann, J. G.↗
NASA NTRS1978

Energetic protons associated with interplanetary active regions 1-5 AU from the sun

Pioneer 11 has yielded data on approximately 100 energetic proton events at heliocentric distances between 1 and 2 AU. Measurements of absolute intensities, anisotropies, and crude energy spectra are studied in connection with interplanetary active regions (IAR's). It is found that in close vicinity to IAR's, the number of events observed per unit time interval is 10 times greater than in other areas of interplanetary space, and that the frequency of events has a maximum at plus or minus 5 hours of the time IAR edges are crossed. It is also noted that events in IAR vicinity have greater particle densities, softer energy spectra, and smaller time widths than other events. For many events associated with IAR's, particle anisotropies correspond to the net flow of particles along the interplanetary magnetic field toward the sun. This suggests that a mechanism in MHD shocks is responsible for local acceleration in the interplanetary medium.

Pesses, M. E.↗
NASA NTRS1976

Solar cosmic ray measurements at high heliocentric latitudes

A brief review is presented of what might result from a program of solar cosmic ray observations on 'out-of-the-ecliptic' spacecraft. The following topics are discussed: (1) The magnetic fields of the sun at high latitudes, (2) propagation of fast charged particles in the solar corona and in interplanetary space at high latitudes, (3) origin of interplanetary particle populations and the solar wind, (4) other particle phenomena in interplanetary space (e.g., acceleration of shock waves), and (5) effect of spacecraft mission characteristics on solar cosmic ray studies at high latitudes. Maps of polar coronal magnetic fields are shown.

Anderson, K. A.↗
NASA NTRS1983

ISEE/IMP observations of simultaneous upstream ion events

Propagation of upstream energetic (50-200 keV) ions is analyzed in sixteen events observed simultaneously by solid state detectors on ISEE 3 at about 200 earth radii and on IMP 8 at about 35 earth radii from the earth. Conclusions are based on comparisons of the pitch angle distributions observed at the two spacecraft and transformed into the solar wind frame. They are beamlike at ISEE 3 and are confined to the outward hemisphere. When IMP 8 is furthest from the bow shock, they are also usually beamlike, or hemispheric. However, when IMP 8 is closer to the bow shock, pancakelike distributions are observed. This systematic variation in the IMP 8 pitch angle distributions delimits a scattering region l less than about 15 earth radii upstream of the earth's bow shock (l measured along the interplanetary magnetic field) that dominates ion propagation, influences the global distribution of fluxes in the foreshock, and may play a role in acceleration of the ions. When IMP 8 is beyond l of about 15 earth radii the propagation appears to be essentially scatter-free between IMP 8 and ISEE 3; this is deduced from the absence of earthward fluxes at IMP 8 as well as the tendency for the spin-averaged fluxes to be comparable at the two spacecraft.

Mitchell, D. G.↗