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At least 667 records · Page 37
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NASA NTRS1975

Time-dependent 2.2-MeV and 0.5-MeV lines from solar flares

The time dependences of the 2.2- and 0.51-MeV gamma-ray lines from solar flares are calculated, and the results are compared with observations of the 1972 August 4 and 7 flares. The time lag between the nuclear reactions and the formation of these two lines is caused by capture of the neutrons and subsequent deceleration of the positrons and decay of the radioactive nuclei. Our main results are that the calculation is consistent with the observed rise of the 2.2-MeV line on August 4, and it does not require different time dependences for the accelerated protons and high-energy electrons in the flare region. The above lags can explain the delayed gamma-ray emission observed on August 7. Positrons of energies greater than about 10 MeV could be detected in interplanetary space following large solar flares.

Wang, H. T.↗
NASA NTRS1976

A two-region model of the solar wind including azimuthal velocity

The two-region model of the solar wind divides the interplanetary space into two regions: it assumes that the solar wind is one-fluid in an inner region within 0.4 AU and two-fluid in an outer region beyond 0.4 AU. This paper includes the angular motion of the solar wind in the two-region model. The flow in the one-fluid region is governed by the one-fluid magnetohydrodynamic equations. The second and third moment equations of the Vlasov equation together with other conservation equations are used to describe the solar-wind flow in the two-fluid region. The predicted azimuthal velocity at 1 AU is less than 2 km/s. All other macroscopic and microscopic properties from this model are in good agreement with experimental quiet-time observations at 1 AU. The numerical results also confirm that when the azimuthal velocity is included in the analysis, the amount of magnetic-field energy converted into kinetic energy in the solar wind is only a small fraction of the total expansion energy flux and has little effect upon the final radial expansion velocity.

Acuna, M. H.↗
NASA NTRS1975

The relative abundances of galactic cosmic ray Be-7, Be-9, and Be-10

The isotopic composition of galactic cosmic ray Be near 100 MeV/nucleon was measured in interplanetary space with high-resolution solid-state telescopes on the IMP-7 and IMP-8 satellites during 1973-1974. These two independent measurements yield Be-10/Be ratios above 10%. Taken together with the galactic propagation model described in the text, these results show that the cosmic ray 'clock' lifetime (most probable value of roughly 20 million years) is significantly greater than that deduced for a nominal interstellar gas density of about 1 to 3 atoms/cu cm.

Garcia-Munoz, M.↗
NASA NTRS1975

Simulation of the velocity diffusion of charged particles in turbulent magnetic fields

Numerical simulation experiments have been performed in order to study the velocity diffusion of charged particles in a static turbulent magnetic field. By following orbits of particles moving in a large ensemble of random magnetic field realizations with suitably-chosen statistical properties, a pitch-angle diffusion coefficient is derived. Results are presented for a variety of particle rigidities and r.m.s. random field strengths and a power spectrum typical of conditions found in interplanetary space.

Kaiser, T. B.↗
NASA NTRS1975

Measurements of cosmic ray anisotropies from Pioneers 10 and 11

A progress report is presented on cosmic ray anisotropy measurements performed in interplanetary space on the Pioneers 10 and 11. A directional Cerenkov counter, sensitive to protons and alpha particles with kinetic energies exceeding 480 MeV/nucleon, was used to determine east-west and north-south anisotropies. Large variations in anisotropies with a time scale of about 60 days were found for the period April-November 1973. The total data set shows an east-west anisotropy of 0.46 plus or minus 0.11% and a north-south anisotropy of 0.03 plus or minus 0.11%. This result for the east-west anisotropy is compatible with a large value of the ratio of the perpendicular to the parallel components of the diffusion coefficient.

Axford, W. I.↗
NASA NTRS1975

A field-ionization neutral detector - FIND

The field ionization neutral detector FIND operates according to the following principle: Neutral atoms are attracted toward the field ionization tips since they are polarized by the electric field of the tips. The atoms are singly ionized and repelled by the positive potential of the tips toward the detector situated behind a grid at ground potential. The ions deposit in the detector their kinetic energies, typically 26 keV, corresponding to the potential difference between the ionization region and the detector. Laboratory results show that FIND can have the resolution, sensitivities and durability required to perform in situ measurements of neutral H and He fluxes in interplanetary space, cometary halos and exospheres.

Curtis, C. C.↗
NASA NTRS1976

Galactic cosmic-ray intensity 0.99 to 5.26 astronomical units from the sun

The intensity of galactic cosmic radiation in interplanetary space has been observed over the heliocentric radial range 0.99 to 5.26 AU with five Geiger-Mueller tubes on Pioneer 10 and over the range 1.00 to 3.59 AU with three similar tubes on Pioneer 11. The observations span the time period 1972 March 3 to 1974 April 29, near the epoch of minimum solar activity. The contributions of solar energetic particles are eliminated. The effect of temporal trends is removed in a variety of ways - by comparison of simultaneous measurements on the two spacecraft; by comparison with data from Explorer 35 at 1.0 AU; and by comparison with terrestrial neutron monitor data. The radial gradient of the intensity of particles with energies greater than 80 MeV/nucleon is zero to within an experimental uncertainty of less than 2 per cent per AU over the range 0.99 to 5.26 AU. Hence, it is less than the theoretically expected value by at least a factor of 5.

Thomsen, M. F.↗
NASA NTRS1976

Longitudinal asymmetry of the Jovian magnetosphere and the periodic escape of energetic particles

An earlier model of the Jovian magnetosphere is utilized in which the centrifugal stress of corotating plasma distends the outer magnetosphere and opens the tail field. Because of a longitudinal asymmetry in the ionospheric plasma source strength, caused principally by the nonaxisymmetric surface field, the closed-field region in the tail expands and contracts with the rotation period, resulting in a 10-hour modulation of the flux of energetic particles escaping from the magnetosphere into interplanetary space.

Hill, T. W.↗
NASA NTRS1977

The streaming of 1.3 - 2.3 MeV cosmic-ray protons during periods between prompt solar particle events

The anisotropy of 1.3 to 2.3 MeV protons in interplanetary space was measured using the Caltech electron/isotope spectrometer aboard IMP-7 for 317 6 hour periods from 72/273 to 74/2. Periods dominated by prompt solar particle events are not included. The convective and diffusive anisotropies were determined from the observed anisotropy using concurrent solar wind speed measurements and observed energy spectra. The diffusive flow of particles was found to be typically toward the sun, indicating a positive radial gradient in the particle density. This anisotropy was inconsistent with previously proposed sources of low energy proton increases seen at 1 AU which involve continual solar acceleration. The typical properties of this new component of low-energy cosmic rays were determined for this period which is near solar minimum.

Marshall, F. E.↗
NASA NTRS1977

Solar-terrestrial interactions

The effects of solar radiation on man's environment are discussed. It is solar radiation that is the basic energy source driving the circulations of the earth's atmosphere and oceans. Solar radiation is responsible for the ionization of the earth's upper atmosphere to form the ionosphere, which is important to our understanding of the magnetosphere and its interaction with the solar wind. The solar wind, which is the continuous (but not steady) flow of the sun's coronal plasma and magnetic field into interplanetary space, plays both an active and passive role in its interaction with the earth's environment.

Source record↗
NASA NTRS1976

Dynamics of the Jovian magnetosphere and energetic particle radiation

Inferences are drawn from Jovian magnetosphere data acquired in the flybys of Pioneer 10 and Pioneer 11. Data on the outer magnetosphere and the inner core, and on observed 10-hr variations in particle intensity, are summarized, with attention given to the immense size and complexity of the magnetosphere and the behavior of trapped charged particles. The data support the maintenance and acceleration of charged particles trapped in Jupiter's magnetic field by inward diffusion in violation of the third adiabatic invariant. Prodigious quantities of high-energy particles are found to escape from Jupiter into interplanetary space, and MHD waves in the circumjovian plasma are considered. Whether the 10-hr variations are spatial or temporal in origin is weighed in favor of the latter. Production and loss mechanisms for the particles, and the nature of the Jovian magnetosphere itself, are noted among questions remaining obscure.

Simpson, J. A.↗
NASA NTRS1976

Observations of energetic Jovian electrons and protons

The Goddard/University of New Hampshire experiment aboard Pioneers 10 and 11 used high and low energy telescopes to measure the nucleon and electron components of the Jupiter magnetosphere. Proton energy spectra are of the form E to the -4th in the outer region and become more complex in the inner region. Particle absorption by several of Jupiter's satellites is an important effect which clearly establishes that radial diffusion is the dominant acceleration process in this region. Observed electron bursts or increases were typically several hundred times the normal quiet-time electron flux, resulting in the quasi-continuous presence of these electrons in interplanetary space. It is suggested that Jupiter could be the source of most of the ambient low energy electrons in the heliosphere.

Mcdonald, F. B.↗
NASA NTRS1976

The Jovian meteoroid environment

Meteoroid fluxes in interplanetary space at 5 AU and near Jupiter have been measured with the penetration detectors on Pioneer 10 and Pioneer 11. The data suggest that the size distribution of meteoroids at 5 AU is the same as that at 1 AU. Furthermore, the high flux observed near Jupiter appears due to meteoroids in orbit about the sun being gravitationally focused toward the planet. There is no indication of a large population of particles in orbit around Jupiter. Calculations show that the mass influx of meteoroids on Jupiter is 170 times that on the earth, but this does not have a significant effect on the energy balance of Jupiter. The high speed with which meteoroids enter the Jovian atmosphere causes them to be brighter than those on earth so that the number of visible meteors is 5800 times the number in the earth's atmosphere.

Humes, D. H.↗
NASA NTRS1977

The lifetime of ice particles in the solar system

The behavior of spherical water-ice particles in interplanetary space is investigated theoretically using an equation which gives the sublimation rate as a function of the solar energy distribution at 1 AU, solar distance, the temperature of the ice-particle surface, the temperature of the surrounding background, particle absorption efficiency, particle radius, and the complex refractive index of ice. The variation of sublimation rate with particle size is examined, and it is shown that the sublimation rate depends critically on the absorptivity of ice in the near-IR spectral region. Two different spectral-absorption curves are plotted on the basis of two different choices for the complex refractive index of ice, and an attempt is made to decide experimentally which energy distribution is more appropriate. Results of direct laboratory measurements of the sublimation rate of smooth spherical ice particles are compared with the theoretical results obtained from the cited sublimation-rate equation. Agreement between theory and experiment is found to be excellent when the complex refractive indices given by Bertie et al., (1969) are employed. Sublimation rates and particle lifetimes are then computed as a function of particle radius for heliocentric distances of 0.5, 0.75, and 1.0 AU.

Patashnick, H.↗
NASA NTRS1976

Low-energy particle events associated with sector boundaries

Onsets of some 40 to 45 low-energy proton events during the years 1957-1969 coincided in time with transits of well-defined sector boundaries across the earth. These events can be interpreted as long-lived proton streams filling up some of the magnetic sectors, indicating an acceleration of protons which is not associated with typical proton-producing flares. The sharp onsets of these particle streams, as well as a deficiency of flare-associated particle events shortly before the boundary transit, indicate that in some cases magnetic sector boundaries can inhibit transverse propagation of low-energy particles in the solar corona or in interplanetary space.

Svestka, Z.↗
NASA NTRS1977

Consequences of using nonlinear particle trajectories to compute spatial diffusion coefficients

In a study of cosmic ray propagation in interstellar and interplanetary space, a perturbed orbit resonant scattering theory for pitch angle diffusion in a slab model of magnetostatic turbulence is slightly generalized and used to compute the diffusion coefficient for spatial propagation parallel to the mean magnetic field. This diffusion coefficient has been useful for describing the solar modulation of the galactic cosmic rays, and for explaining the diffusive phase in solar flares in which the initial anisotropy of the particle distribution decays to isotropy.

Goldstein, M. L.↗
NASA NTRS1978

A three-dimensional model of corotating streams in the solar wind. 1: Theoretical foundations

The theoretical and mathematical background pertinent to the study of steady, corotating solar wind structure in all three spatial dimensions (3-D) is discussed. The dynamical evolution of the plasma in interplanetary space (defined as the region beyond roughly 35 solar radii where the flow is supersonic) is approximately described by the nonlinear, single fluid, polytropic (magneto-) hydrodynamic equations. Efficient numerical techniques for solving this complex system of coupled, hyperbolic partial differential equations are outlined. The formulation is inviscid and nonmagnetic, but methods allow for the potential inclusion of both features with only modest modifications. One simple, highly idealized, hydrodynamic model stream is examined to illustrate the fundamental processes involved in the 3-D dynamics of stream evolution. Spatial variations in the rotational stream interaction mechanism were found to produce small nonradial flows on a global scale that lead to the transport of mass, energy, and momentum away from regions of relative compression and into regions of relative rarefaction.

Pizzo, V. J.↗
NASA NTRS1977

Voyager mission description

The Voyager project, which involves the 1977 launch of two advanced three-axis attitude stabilized spacecraft for the exploration of the Jovian and Saturnian systems, as well as interplanetary space, is discussed. The missions include investigation of the gravitational fields, atmospheric dynamics and magnetospheres of Jupiter and Saturn, the atmospheres, surface composition and features of Titan, the Io flux tube, the Great Red Spot of Jupiter, and earth occultation by Saturn's rings. To reduce energy required to reach Saturn, gravity-assist swingbys of Jupiter will be employed; a continuation to Uranus by the second satellite may be implemented by reliance on gravity-assist at Saturn.

Kohlhase, C. E.↗