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NASA NTRS1973

Directional diffusion coefficients of solar protons inside and outside the bow shock.

The directional diffusion coefficients of low-energy (greater than or equal to 0.3 MeV) solar protons inside and outside the bow shock are examined during the solar flare event of Jan. 24, 1969. The data are derived from simultaneous observations obtained by Explorer 33 inside the magnetosheath and by Explorer 35 in the interplanetary medium. Although the gross properties of the spin-averaged intensities on a diffusion-type plot appear to be the same in both media, the directional intensities show significant variations. It is shown that directional intensities of low-energy protons can be described reasonably well by anisotropic diffusion with an associated diffusion coefficient. Directional diffusion coefficients are found to differ by a factor of as much as three among different directions in space, and from the spin-averaged diffusion coefficient. This suggests that anisotropic diffusion does indeed take place and that so called 'isotropic' diffusion coefficients derived in the past from spin-averaged intensities may actually be directional diffusion coefficients in cases where substantial anisotropies (greater than 50%) exist.

Verzariu, P.↗

NASA NTRS1973

Analysis and synthesis of coronal and interplanetary energetic particle, plasma, and magnetic field observations over three solar rotations.

In a previous paper (Krimigis et al., 1971), simultaneous observations in 1967 of solar particle events at low (less than 1 MeV) energies were presented. In the present paper, the full complement of simultaneous plasma, magnetic field, and energetic particle data is combined, and a complete analysis is made of all the events discussed in the original paper. The essential concept of 'collimated convection' is introduced, whereby the bulk velocity along the field lines of low-energy solar particles is independent of solar local plasma velocity, and the particles are strongly collimated along the field line with no transverse velocity component other than that of the field line itself. Collimated convection effects are shown to exist in small-scale convection and large-scale evolution of particle fluxes; the particle fluxes are, in turn, used to delineate the small-scale and large-scale evolution of the interplanetary magnetic field. Use of collimated convection is made in demonstrating a technique whereby energetic particle intensity profiles in the interplanetary medium can be related to equatorial high coronal magnetic field structures, by using the instantaneous solar wind velocity. This technique is applied in mapping particle intensities from Mariner 5 onto H alpha synoptic charts of chromospheric magnetic field structures for Carrington rotations 1523 to 1525.

Roelof, E. C.↗

NASA NTRS1973

Apollo 16 far-ultraviolet camera/spectrograph - Instrument and operations.

A far-ultraviolet camera/spectrograph experiment was designed and constructed for studies of the terrestrial upper atmosphere and geocorona, the interplanetary medium, and celestial objects from the lunar surface. The experiment was successfully operated during the Apollo 16 mission 21-23 April 1972. Discussed are the design and operating principles of the instrument, the actual events and operations during the Apollo 16 mission, and also anomalies encountered and suggested improvements for future experiments of this type. This experiment demonstrated the utility of the electronographic technique in space astronomy, as well as the great potential of the lunar surface as a base for astronomical observations.

Carruthers, G. R.↗

NASA NTRS1973

Electron observations in the solar wind and magnetosheath.

Electron temperature measurements taken by a triaxial electron analyzer on Ogo 5 in the solar wind and in the magnetosheath are interpreted. In the interplanetary medium, observations made on the bow shock connected lines of magnetic force have been separated from those made on non-bow-shock connected lines. The dependence of electron thermal properties on the local field geometry is discussed together with features of electron temperature and density discontinuities across the bow shock. The velocity distribution function is characterized together with temperature and density variations in a part of the dawn magnetosheath.

Scudder, J. D.↗

NASA NTRS1973

The remote sensing of Saturn's rings. 1: The magnetic alinement of the ring particles

Because of the potential implications for the optical properties of Saturn's rings, the orientation of nonspherical ring particles at equilibrium is investigated with respect to four stochastic influences: interactions with the interplanetary medium, interactions with the expected magnetic field of Saturn, thermal fluctuations due to the internal temperature of the ring particles; collisions between ring particles. The solution of the homogeneous Fokker-Planck equation for nearly spherical spheroids is presented and investigated in general. Values of the pertinent physical parameters in the vicinity of Saturn are estimated, and the implications for the alignment of the ring particles are investigated. It is concluded that for some alignment mechanisms, small ring particles can be expected to be almost completely aligned. This alignment results in each particle spinning around its shortest body axis with this axis parallel to the magnetic field direction (perpendicular to the ring plane).

Evans, L. C.↗

NASA NTRS1973

Low frequency gyro-synchrotron radio noise from the earth's outer radiation belt

The problem of detecting cyclotron and synchrotron noise from superthermal electrons is analyzed for the frequency range 30 kHz 300 kHz. Due to the earth's ionosphere, ground based observation of this noise is improbable. Therefore, the calculations are made for an observer in the interplanetary medium. In particular, the location is chosen in the geomagnetic equatorial plane at a geocentric distance of 32 earth radii. This position of the observer allows the theoretical results to be compared directly with data obtained from the radio astronomy experiment aboard the IMP-6 spacecraft.

Frankel, M. S.↗

NASA NTRS1974

Charged particles

Calibrations compensating for the effects of charged particles in the ionosphere and in the interplanetary medium were applied to the Doppler tracking data acquired during Mariner 9 missions on a demonstration basis. The combined effects of the space plasma and the ionosphere were measured by a comparison of the range and Doppler observables (Differenced Range Versus Integrated Doppler (DRVID). Independent measurements of the ionospheric effects were obtained from polarimeter devices located at the Goldstone, California, tracking complex.

Madrid, G. A.↗

NASA NTRS1973

The relationship of solar flare electrons to the flare flash phase and type 3 radio bursts

The energy spectrum and temporal behavior of the 10 to 100 keV solar flare electrons observed at 1 AU are interpreted in terms of: (1) the location of the acceleration region, (2) the time of acceleration and duration of the injection into the interplanetary medium, and (3) type 3 radio burst origin at the sun and at 1 AU. For at least some and possibly the majority of electron flare events the density of the acceleration region is approximately 2 X 10 to the 9th power cu/cm, the time of acceleration and release coincides to within minutes of the flash phase as indicated by the type 3 radio burst, and the duration of the release less than or approximately 3 minutes. Evidence for the origin of type 3 radio bursts in 10 to 100 keV electron streams is shown and discussed.

Lin, R. P.↗

NASA NTRS1972

Microwave conductivity of slightly ionized gases and electromagnetic scintillations

Two areas of research are briefly summarized. The first is concerned with calculating the conductivity of a slightly ionized gas. A method is proposed which involves an expansion of the Boltzmann collision operator (of the electron distribution function, involving the neutral gas-electron interactions) in powers of the electron-gas mass ratio. The second area of investigation focuses on the problem of a radio wave propagating through the interplanetary medium, taking account of the decreasing plasma density with distance from the sun.

Mintzer, D.↗

NASA NTRS1973

Characteristics of type III exciters derived from low frequency radio observations

Low-frequency radio observations (2.8 MHz to 67 kHz) from the RAE-1 and IMP-6 satellites allow the tracking of type III solar burst exciters out to large distances from the sun (of the order of 1 AU). A study of the interaction processes between the exciter and the interplanetary medium was made using the time-intensity profiles of the radio emission. The change in exciter length with distance from the sun, and the resulting exciter velocity dispersion which can be deduced from this change are investigated. From detailed measurements on 35 simple bursts it is found that the exciter length increases at a faster rate than a constant velocity dispersion would give. The damping of the radio emission is also investigated, and it is concluded that some current theories of the damping mechanism give results which are not consistent with the low-frequency observations.

Evans, L. G.↗

NASA NTRS1973

Lunar electromagnetic scattering. II - Magnetic fields and transfer functions for parallel propagation

Magnetic field and transfer function amplitudes, resulting from a transverse electromagnetic wave in the interplanetary medium scattering from the moon and its diamagnetic cavity, are presented. Calculations are made using an asymmetric scattering theory for a spherical two-layer model of the lunar electrical conductivity profile and a nonconducting cylindrical model of the downstream lunar plasma void. Both the field and transfer function magnitudes are calculated as functions of position on the surface of the moon for frequencies relevant to the observations of the lunar surface and orbiting magnetometers. The amplitudes of the magnetic field components on the cavity boundary are also computed as functions of frequency and distance downstream from the lunar limb. Comparisons of the results are made with those of (1) spherically symmetric descriptions of lunar electromagnetic scattering, (2) the quasi-static approximation to asymmetric scattering theory, and (3) observations of the scattering phenomenon by lunar surface and orbiting magnetometers.

Schubert, G.↗

NASA NTRS1974

Isotopic composition of low energy beryllium in the galactic cosmic rays

The multielement charged-particle telescope on the IMP-5 satellite obtained data essentially continuously for more than three years in the interplanetary medium under stable instrument conditions which have made it possible to separate the H, He, and Be isotopes in the galactic cosmic radiation using the technique of double dE/dx vs residual E and particle range measurements. Special emphasis is placed on demonstrating that in the energy range from 50 to 150 MeV/nucleon the instrument clearly resolved Be-7 vs Be-9. A detailed analysis of approximately 100 Be events collected over the mission lifetime yields the ratios (Be-7/Be) = 0.50 plus or minus 0.07, (Be-9/Be) = 0.41 plus or minus 0.10, and (Be-10/Be) = 0.09 plus or minus 0.10. These results are consistent with current models of galactic cosmic ray propagation after taking account of the effects of solar modulation.

Garcia-Munoz, M.↗

NASA NTRS1974

Analytic approximations in the study of the solar modulation of electrons

Numerical solutions to the transport equation of galactic cosmic rays in the interplanetary medium have been used to investigate the applicability of commonly used approximate analytic solutions for electrons (10 MeV to 10 GeV). We find that for a given cosmic-ray diffusion coefficient the force-field approximation is in reasonable agreement with the numerical solution at energies above 200 MeV, but deviates significantly at lower energies, depending on the shape of the interstellar electron spectrum. The diffusion-convection approximation agrees generally with the numerical solution within a factor of 2 over the entire energy range.

Cummings, A. C.↗

NASA NTRS1974

Large-amplitude hydromagnetic waves

Several aspects of the theory of large-amplitude hydromagnetic waves and their behavior in the interplanetary medium are examined. The characteristic modes of the full (i.e., nonlinearized) MHD equations and their modification by collisionless and finite-frequency effects are considered. Special attention is paid to the transverse Alfven mode, which is undamped and characterized by strictly constant pressure, density, and B; this seems to be the predominant propagating fluctuation at 1 AU. It is shown that its propagation in the small-wavelength (WKB) approximation is essentially identical to that of the small-amplitude Alfven wave of linearized theory. It is also suggested that its presence at 1 AU may provide a natural explanation of the observed power anisotropy of the fluctuations. A second-order analysis is used to study fluctuations that are not characteristic modes. It is found that for a small range of propagation directions, and subject to third-order effects, a finite-amplitude wave can exist that is linearly polarized with delta B perpendicular to both B sub zero and k; such a wave can damp nonlinearly.

Barnes, A.↗

NASA NTRS1974

The origin of life in a cosmic context

It is shown that there is at present no aspect of contemporary biology where the contingent can be distinguished from the necessary, or the evolutionary accident from the biological sine qua non; and no amount of terrestrial experimentation alone is likely to make such distinctions possible. Hence, biology suffers from a deadening parochialism, much like the physics of falling bodies before Newton showed that the same laws applied to the motion of apples in England and to the planets about the sun. The deparochialization of biology can only come in the same way and must therefore await the search for extraterrestrial life. It is in this sense that the significance of explorations of the planets and their satellites, asteroids, comets, and the interplanetary medium for the origin of life is assessed.

Sagan, C.↗

NASA NTRS1973

Pioneer F and G spacecraft

Two spacecraft, Pioneers F and G, each with a launch weight of approximately 256 kg, were launched in March 1972 and April 1973 on trajectories which will result in close Jupiter encounters in late 1973 and 1974, respectively. The Pioneer mission objectives are to investigate the interplanetary medium beyond Mars, to determine the nature of the asteroid belt, and to explore Jupiter and its environment. A review is given of the system and subsystem design with emphasis on the simplicity of design, the selective use of redundancy for reliability enhancement, and the environmental protection provided.

Obrien, B. J.↗

NASA NTRS1974

Interplanetary stream interfaces

At 1 AU there is a distinct boundary (the stream interface) in the interaction region of a stream in the solar wind, characterized by an abrupt drop in density, a similar increase in temperature, and a small increase in speed. In some cases, this is a tangential discontinuity, in others it is probably evolving into a tangential discontinuity. It is suggested that stream interfaces form in the interplanetary medium as a consequence of the nonlinear evolution of streams generated by an increase in temperature in the solar envelope. This evolution eventually leads to the formation of a reverse shock behind the interface and a forward shock ahead of it. Two instances in which both a stream interface and a reverse shock had developed at 1 AU are presented. Examples of flare-generated shocks that passed through a stream and were observed near a stream interface are also presented. It is shown that stream interfaces are definitely not the same structures that others have identified as piston boundaries.

Burlaga, L. F.↗

NASA NTRS1974

High energy particles and quanta in astrophysics

The various subdisciplines of high-energy astrophysics are surveyed in a series of articles which attempt to give an overall view of the subject as a whole by emphasizing the basic physics common to all fields in which high-energy particles and quanta play a role. Successive chapters cover cosmic ray experimental observations, the abundances of nuclei in the cosmic radiation, cosmic electrons, solar modulation, solar particles (observation, relationship to the sun acceleration, interplanetary medium), radio astronomy, galactic X-ray sources, the cosmic X-ray background, and gamma ray astronomy. Individual items are announced in this issue.

Mcdonald, F. B.↗