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Mckibben, R. B.

Publications and source records attributed to Mckibben, R. B..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

An LDEF 2 dust instrument for discrimination between orbital debris and natural particles in near-Earth space

The characteristics of a space dust instrument which would be ideally suited to carry out near-Earth dust measurements on a possible Long Duraction Exposure Facility reflight mission (LDEF 2) is discussed. As a model for the trajectory portion of the instrument proposed for LDEF 2, the characteristics of a SPAce DUSt instrument (SPADUS) currently under development for flight on the USA ARGOS mission to measure the flux, mass, velocity, and trajectory of near-Earth dust is summarized. Since natural (cosmic) dust and man-made dust particles (orbital debris) have different velocity and trajectory distributions, they are distinguished by means of the SPADUS velocity/trajectory information. The SPADUS measurements will cover the dust mass range approximately 5 x 10(exp -12) g (2 microns diameter) to approximately 1 x 10(exp -5) g (200 microns diameter), with an expected mean error in particle trajectory of approximately 7 deg (isotropic flux). Arrays of capture cell devices positioned behind the trajectory instrumentation would provide for Earth-based chemical and isotopic analysis of captured dust. The SPADUS measurement principles, characteristics, its role in the ARGOS mission, and its application to an LDEF 2 mission are summarized.

Tuzzolino, A. J.↗
NASA NTRS1990

Energetic ion and cosmic ray characteristics of a magnetic cloud

The large interplanetary shock event of February 11, 1982, has yielded ISEE-3 energetic ion and magnetic field data as well as ground-based neutron-monitor cosmic-ray data. The timing and the onset of the Forbush decrease associated with this shock event coincide with the arrival at the earth of its magnetic cloud component; the duration of the decrease, similarly, corresponds to that of the cloud's passage past the earth. The large scattering mean free path readings suggest that while magnetic cloud ions can easily travel along magnetic field lines, they cannot travel across them, so that they cannot escape the cloud after entering it. Similarly, the cloud field lines prevented cosmic ray entrance, and could have prevented their reaching the earth. The cloud is therefore a major basis for the Forbush decrease.

Sanderson, T. R.↗
NASA NTRS1989

Reanalysis and confirmation of positive latitude gradients for anomalous helium and Galactic cosmic rays measured in 1975-1976 with Pioneer II

Reanalysis of the 1975-1978 observations from Pioneer 10, Pioneer 11, and IMP 8 confirm earlier reports of a positive latitude gradient during this period for low-energy anomalous helium and, possibly, for low-energy Galactic protons. The observations are most consistent with an intensity distribution that is asymmetric with respect to the heliographic equatorial plane, rather than symmetric, as had been assumed in the earlier reports, and as would be most naturally consistent with currently available models for the solar modulation. Attempts to relate the intensity to the relative positions of the spacecraft with respect to the interplanetary equatorial neutral sheet yield no improvement in the organization of the data.

Mckibben, R. B.↗
NASA NTRS1988

Toward a descriptive model of galactic cosmic rays in the heliosphere

Researchers review the elements that enter into phenomenological models of the composition, energy spectra, and the spatial and temporal variations of galactic cosmic rays, including the so-called anomalous cosmic ray component. Starting from an existing model, designed to describe the behavior of cosmic rays in the near-Earth environment, researchers suggest possible updates and improvements to this model, and then propose a quantitative approach for extending such a model into other regions of the heliosphere.

Mewaldt, R. A.↗
NASA NTRS1988

Gradients of galactic cosmic rays and anomalous components

Measurements of radial and latitudinal gradients of galactic cosmic rays and anomalous components now cover radii from 0.3 to 40 AU from the sun and latitudes up to 30 deg above the ecliptic plane for particle energies from approx. 10 MeV/n up to relativistic energies. The most accurate measurements cover the period 1972 through 1987, which includes more than one full 11 year cycle of solar activity. Radial gradients for glactic cosmic rays of all energies and species are small (similar to less than 10 percent AU), and variable in time, reaching a minimum of near 0 percent AU out to 30 AU for some species at solar maximum. Gradients for anomalous components are larger, of order 15 percent AU, may show similar time variability, and are relatively independent of particle species and energy. For the period 1985 through 1986 the intensity decreased away from the ecliptic for all species and energies. For galactic cosmic rays, the measured gradients are approx. 0.5 percent/degree near 20 AU, while for anomalous components the gradients are larger, ranging from 3 to 6 percent/degree. Comparison with a similar measurement for anomalous helium in 1975 through 1976 suggests that the latitude gradients for anomalous components have changed sign between 1975 and 1985. For galactic cosmic rays, the available evidence suggests no change in sign of the latitudinal gradient for relativistic particles.

Mckibben, R. B.↗
NASA NTRS1987

Solar modulation of the cosmic radiation in the heliosphere

Changes in the solar modulation of galactic and anomalous component cosmic rays reflect changes in the structure and magnetic topology of the interplanetary medium. Therefore, to the extent that the modulation process is understood, the cosmic rays can be used as a probe of the medium to infer the extent and structure of the heliosphere in regions not directly sampled by spacecraft. The challenge to modulation theory and observation has been to determine which properties of the solar wind are most important for producing the observed modulation. Significant progress has been made in answering this question during the last solar cycle using observations from spacecraft at radii to 40 AU from the Sun and at latitudes up to 30 degrees with respect to the ecliptic. A brief summary of new results and observations (with specific attention to the STIP intervals XV-XIX) will be presented to illustrate the present state of our understanding of the relation between the solar wind and interplanetary magnetic field and the modulations of the cosmic radiation.

Mckibben, R. B.↗
NASA NTRS1987

Galactic cosmic rays and anomalous components in the heliosphere

The progress made during 1983-1986 by U.S scientists on modulation of Galactic cosmic rays by the sun and on the origin, acceleration, and modulation of the anomalous components in the heliosphere is reviewed. In these years, simultaneous observations of modulation, covering a radial range from 1 to more than 30 AU and a heliospheric latitude range from 0 to greater than 20 deg, made it possible to investigate directly the dynamics and spatial scale of modulation during both the increasing and declining phases of solar activity and to make in situ correlations between changes in the interplanetary medium and changes in the modulation of cosmic rays. Particular attention is given to the use of the observations related to time-dependent modulation effects, curvature drifts, and anomalous components, as well as of the measurements of the cosmic-ray radial gradients and latitudinal intensity variations, in the modeling of solar modulation effects.

Mckibben, R. B.↗
NASA NTRS1986

Pionener 11 observations of effects of Ganymede and Callisto on Jupiter's trapped radiation

Charged particle data for low-energy protons and electrons from the Pioneer 11 high-latitude flyby of Jupiter in 1974 are reviewed in the light of the Voyager 1 magnetic field model of Connerney et al. (1981). It is found that if the trajectory of Pioneer 11 is mapped to the equatorial plane along the model magnetic field lines, significant features in the time-intensity profiles of trapped protons and electrons, including one microsignaturelike feature, are found to correspond to shells of closed field lines crossed by the orbits of Ganymede and Callisto. It is suggested that these features are signatures of interaction of the trapped particles with Ganymede and Callisto.

Mckibben, R. B.↗
NASA NTRS1986

Modulation of galactic cosmic rays in the heliosphere

Observations of the intensity of galactic cosmic rays and anomalous components near earth and in the outer heliosphere are providing important tests for theories of solar modulation. The most recent observations show effects that seem to require that models for modulation include gradient and curvature drifts as well as the conventional processes of convection, adiabatic deceleration, and diffusion. New observations are required to define the interplay of these processes in the three-dimensional heliosphere.

Mckibben, R. B.↗
NASA NTRS1985

Galactic cosmic ray radial gradients and the anomalous He component near maximum solar modulation and to radii beyond 34 AU from the Sun

Radial gradients for relativistic galactic cosmic rays (E 70 MeV) remained nearly constant at approx. 2.5%/AU from 1978-84, which includes the period of maximum solar modulation in 1981-82. For energies 30-70 MeV/n, gradients decreased at solar maximum to values of 1%/AU (protons) and 4%/AU (helium), and appear to be increasing again in 1983-84 toward the values found for solar minimum. The anomalous helium component has not reappeared, either at 1 AU or at Pioneer 10 at R 34 AU.

Mckibben, R. B.↗
NASA NTRS1985

Changes in radial gradients of low-energy cosmic rays between solar minimum and maximum: - Observations from 1 to 31 AU

Observations of the fluxes and radial gradients of protons and helium (with energies of 10-70 Mev per n) between the period of minimum solar modulation ending in 1977 and the period of maximum modulation in 1981-1983 show that, over the radial range 1-31 AU, radial gradients decreased for both species from their solar minimum values (5-10 percent per AU for galactic protons and helium) to values of 2-4 percent per AU or less. For these low-energy cosmic rays it is found that the variation in modulation with the phase of the solar cycle is much stronger at radii of 20-30 AU than at 1 AU, and that at solar maximum, more than 99 percent of the total modulation takes place beyond 31 AU.

Mckibben, R. B.↗
NASA NTRS1983

Pioneer 11 observations of trapped particle absorption by Amalthea

The discovery of a microsignatury of trapped radiation in the Amalthea orbit as detected by Pioneer 11 in a flyby of Juptier in 1974 is reported and its implications for the radial diffusion coefficient in Jupiter's inner magnetosphere are discussed. A low energy telescope registered the absorption of low-energy protons as a function of the magnetic L shell durig inbound and outbound trajectories. Drift velocities of the 1 MeV particles were calculated. No correspondingly heightened effects were observed from high-energy electrons or heavier nuclei. Further analysis of the 0.5-8.7 MeV protons showed data to be consistent erosion of the particle drift shadows by a diffusion process. A limit was calculated for the highest diffusion coefficient value for the 1 MeV protons at the Amalthea orbit. The results indicate that the diffusion is driven by fluctuating electric or magnetic fields.

Mckibben, R. B.↗
NASA NTRS1983

Pioneer 11 observations of trapped particle absorption by the Jovian ring and the satellites 1979, J1, J2, and J3

Pioneer 11 low energy telescope observation of charged particles around the Jovian satellites Amalthea, 1979 J1, J2, and J3, and the Jupiter ring are examined in the light of Voyager optical data from the same region. Good agreement was found in the absorption features of 0.5-8.7 MeV protons, electrons with energies of 3.4 MeV or more, and medium-Z nuclei. The heavier nuclei are suggested to be oxygen and sulfur particles with energies exceeding 70 MeV/nucleon. The observed intensity features in the regularly spaced radiation bands are interpreted as ring and satellite absorption.

Pyle, K. R.↗
NASA NTRS1983

Radial gradients of galactic cosmic rays measured by Pioneer 10 from 1-29 AU through the period of solar maximum

During the approach to maximum solar modulation in 1982, the radial gradient of high energy galactic cosmic rays gradually increased to about 2.5 percent/AU from the solar minimum value of about 1.5 percent/AU. In the same period, at energies lower than 70 MeV/n, the radial gradients for protons decreased from about 8 percent/AU to about 1 percent/AU. It is found that at solar maximum, in contrast to solar minimum, essentially all of the modulation of low energy cosmic rays occurs outside R = 29 AU. The combined effects of solar flare shocks coalescing in the far outer heliosphere may account for this dramatic change in the radial dependence of modulation.

Mckibben, R. B.↗
NASA NTRS1982

The heliospheric intensity gradients of the anomalous He4 and the galactic cosmic-ray components

Measurements made with Pioneers 10 and 11 over the radial range of 1 to about 25 AU from 1972 to 1981 are presented to show that at solar minimum (1972-1977), the radial gradient for the anomalous helium component from 11 to 20 MeV/n is about 14%/AU. This result is significantly smaller than that predicted for either charge state of the component based on the observed spectrum and assumptions of conventional solar modulation for particles propagating inward from the heliospheric boundary. It is confirmed that the solar modulation mechanism that determines the level and distribution of low-energy galactic cosmic rays in the heliosphere, also modulates the He(A) spectrum. With increasing modulation between solar minimum and maximum, the 10-20 MeV/n He(A) flux decreases below the flux of modulated galactic He first at 1 AU and then progressively outward to 22-25 AU over an approximately two year period.

Mckibben, R. B.↗
NASA NTRS1982

The galactic cosmic-ray radial intensity gradient and large-scale modulation in the heliosphere

Measurements of fluxes from 1 AU on the IMP 8 satellite to 11 AU on the Pioneer 11 and to greater than 24 AU on the Pioneer 10 spacecraft show that the nucleon integral gradient is a function of the level of the approximately 11-year solar modulation cycle. The gradient decreases from approximately 4.5% to 1.5% throughout the solar minimum of 1975-1977, and increases to approximately 2.5-3.0% per AU near maximum modulation. Pioneer 10 at greater than 24 AU is still deep in the modulation region, leading to estimates of 50-70 AU for the radial distance to the heliopause at both solar minimum and solar maximum modulation.

Mckibben, R. B.↗
NASA NTRS1982

Gradients of galactic cosmic rays and anomalous helium to more than 23 A.U. during the increase of solar modulation in 1978-80

During the transition to solar maximum (1978-81) the radial gradient of high energy galactic cosmic rays increased slightly, while the gradients of lower energy cosmic rays and the anomalous helium decreased. It is concluded that (1) Pioneer-10 at about 23 AU was still deep in a modulation region extending to more than 50 AU for both the galactic cosmic rays and the anomalous helium component, and (2) the modulation is controlled by changes in the size/geometry of heliospheric magnetic fields and/or propagation parameters, changes associated with large solar-flare shocks in 1978 and later.

Bastian, T. S.↗