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  • 1
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    Energetic water-group ions at Comet Giacobini-Zinner - An overview of observations by the EPAS instrument (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: An overview is presented of the observations of energetic (45-480 keV) cometary water group ions made by the EPAS instrument on the ICE spacecraft during the fly-by of Comet Giacobini-Zinner in September 1985. The discussion covers ion observations in the large-scale ion pick-up region surrounding the comet on about 10 exp 6 km spatial scales, observations of the cometary shock at about 100,000 km and the region of slowed mass-loaded flows which occur downstream, and the finite gyroradius effects which occur near the closest approach.
    Keywords: ASTROPHYSICS
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  • 2
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    Comparison of magnetosonic wave and water group ion energy densities at Comet Giacobini-Zinner (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Measurements of the Comet Giacobini-Zinner (GZ) are presented to determine to what extent wave-particle scattering redistributed the initial pick-up energy of the ion population. Also examined is the difference between the ion thermal energy and the energy in the magnetic fields of the waves. In spite of uncertainty of about a factor of 2 noted in the pick-up and mass-loaded regions, it is shown that less than approximately 50 percent of the pick-up energy is converted into wave magnetic energy in the inbound pick-up region.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 11; 9, 19; 83-86
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  • 3
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    Properties of a large-scale interplanetary loop structure as deduced from low-energy proton anisotropy and magnetic field measurements (1987)
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    Publication Date: 2011-08-19
    Description: Correlated particle and magnetic field measurements by the ISEE 3 spacecraft are presented for the loop structure behind the interplanetary traveling shock event of Nov. 12, 1978. Following the passage of the turbulent shock region, strong bidirectional streaming of low-energy protons is observed for approximately 6 hours, corresponding to a loop thickness of about 0.07 AU. This region is also characterized by a low relative variance of the magnetic field, a depressed proton intensity, and a reduction in the magnetic power spectral density. Using quasi-linear theory applied to a slab model, a value of 3 AU is derived for the mean free path during the passage of the closed loop. It is inferred from this observation that the proton regime associated with the loop structure is experiencing scatter-free transport and that either the length of the loop is approximately 3 AU between the sun and the earth or else the protons are being reflected at both ends of a smaller loop.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 6-14
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  • 4
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    In-situ observations of cometary pick-up ions greater than 0.2 AU upstream of Comet Halley - ICE observations (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Burst-like enhancements of energetic ions were observed by the EPAS instrument on the International Cometary Explorer (ICE) during its closest approach to (28 x 10 to the 6th km upstream of) Comet P/Halley, in late March 1986. The ion intensity was modulated by the varying solar wind speed (the latter reaching maxima of around 600 km/s), as was found to be the case for heavy cometary ions accelerated by pick-up in the solar wind flow, during the ICE encounter with Comet P/Giacobini-Zinner (G-Z). Therefore it is concluded that the observed pick-up ions (most probably greater than or equal to 65 keV oxygen ions) are produced by heavy neutrals from Comet Halley. The observations of energetic ions at such large distances suggest the presence, in the neutral atmosphere surrounding the nucleus, of a component with an ionization scale length of 5-10 million km, resulting from a relatively high expansion speed of a few km/s and/or an ionization time scale of a few times 10 to the 6ths.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 13; 861-864
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  • 5
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    Observations of the interactions of heavy ions from Comet P/Giacobini-Zinner with the solar wind (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: During the encounter between the ICE spacecraft and Comet Giacobini-Zinner, intense fluxes of energetic heavy ions were observed up to 4 x 10 to the 6th km from the comet. In this paper the authors correlated observations of heavy ions, the solar wind velocity and the magnetic field direction, and compare the observations of the ions with the theoretical predictions for their variations with distance from the comet, wih the solar wind velocity and with the magnetic field direction.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 1, 19
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  • 6
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    Gyroradius effects on the energetic ions in the tail lobes of Comet P/Giacobini-Zinner (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: It is reported that during the ICE fly-by of comet P/Giacobini-Zinner, a depletion was seen in the energetic ion intensities (E greater than 65 keV for 'water group' ions) extending to about 40 min on either side of the time of closest approach (1102 UT on September 11, 1985). It is demonstrated that the physical size of this hole is a few ion gyroradii (about 1.5 x 10 to the 4 km). Angular analysis of the ion distributions in the 'gyroradius region' can distinguish those ions whose gyromotion is entirely in one comet lobe from those that cross the current sheet into the other lobe. In the central tail within a few minutes of closest approach, the single-lobe ions exhibit high intensities and little pitch angle dependence, whereas the ions crossing the current sheet have lower intensities and are streaming along the magnetic field away from the comet. The derived density gradients are used to determine the orientation of the current sheet at closest approach, as 44 degrees east of north.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 13; 419-422
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  • 7
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    Correlated particle and magnetic field observations of a large-scale magnetic loop structure behind an interplanetary shock (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: From a survey of observations on ISEE-3, an example of correlated particle and magnetic field observations of a large-scale magnetic loop structure is presented. Bidirectional proton fluxes were observed for a period of 40 hours in the energy range 35-1600 keV approximately 12 hours after the passage of the interplanetary shock of December 11, 1980, and directly after the passage of a discontinuity. For each of the eight logarithmically spaced energy channels, a three-dimensional anisotropy analysis reveals streaming along both directions of the magnetic field. The magnetic field rotated slowly but steadily through approximately 180 deg during this same 40-hour period; this is consistent with the existence of a large-scale loop with extent greater than 0.5 AU. The observations suggest that the particles are being injected into the loop sunward of the spacecraft; they appear as bidirectional fluxes in the outermost regions of the loop arising from a combination of focusing and near scatter-free transport.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 10; Sept
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  • 8
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    Observations of heavy energetic ions far upstream from Comet Halley (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: On March 25, 1986, when the ICE spacecraft came within 28 million km of the nucleus of comet Halley, and for several days around this time, bursts of heavy ions were observed by the ICE energetic ion experiment. The bursts were observed only during periods when the solar wind velocity was considerably higher than its nominal value. The characteristics of these ions, in particular their anisotropies, were examined. Using the well known formulae for transformation of distributions from the solar wind frame of reference to the spacecraft frame, the angular distributions expected from either protons, or heavy ions from the water group, were studied, showing that the measurements are consistent with heavy ions, and not with protons. Other sources of heavy ions are considered, and the most likely source of these ions is comet Halley.
    Keywords: ASTROPHYSICS
    Type: ESA Proceedings of the 20th ESLAB Symposium on the Exploration of Halley's Comet. Volume 1: Plasma and Gas; p 105-108
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  • 9
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    The interaction of heavy ions from Comet P/Giacobini-Zinner with the solar wind (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The encounter between the ICE spacecraft and Comet P/Giacobini-Zinner was characterized in the solar wind by intense fluxes of heavy ions, measurable over a region 6 x 10 to the 6th km in extent. The ions are observed with highly anisotropic angular distributions, steep energy spectra, and a change in the energy spectrum at around 80 keV, consistent with a composition predominantly of the water group. Flux versus time profiles follow a general fall off with increasing distance from the comet, but with a marked inbound/outbound asymmetry. This asymmetry is due to the higher solar wind velocity on the outbound pass, giving rise to an increased energy gain of the pick-up ions. The flux versus time profiles are strongly modulated by the rapid changes in the direction of interplanetary magnetic field. Correlated observations of energetic ions, the interplanetary magnetic field and the solar wind are presented, and these observations are compared with theoretical predictions of the ion pick-up process.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 13; 411-414
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  • 10
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    ISEE/IMP observations of simultaneous upstream ion events (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: 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.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 88; July 1
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