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  • ASTROPHYSICS  (35)
  • Lunar and Planetary Science and Exploration  (1)
  • SPACE SCIENCES (GENERAL)  (1)
  • Space Sciences (General)  (1)
  • 1
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    The relationship between interplanetary discontinuities and Alfven waves: Ulysses observations (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The rate of occurrence of interplanetary discontinuities (ROID) is examined using Ulysses magnetic field and plasma data from 1 to 5 AU radial distance from the Sun and at high heliographic latitudes. We find two regions where the ROID is high: in stream-stream interaction regions and in Alfven wave trains. This latter feature is particularly obvious at high latitudes when Ulysses enters a high speed stream associated with a polar coronal hole. These streams are characterized by the presence of continuous, large-amplitude (Delta (vector 13)/absolute value of B is about 1-2 Alfven waves and an extraordinarily high ROID value (approximately 150 discontinuities/day). In a number of intervals examined, it is found that (rotational) discontinuities are an integral part of the Alfven waves. The nonlinear Alfven waves are spherically polarized, i.e., the tip of the perturbation vector resides on the surface of a sphere (a consequence of constant absolute value of B). The slowly rotating part of the wave rotates approximately 270 deg in phase. There is a slight arc in the B(sub 1) - B(sub 2) hodogram, suggesting an almost linear polarization. The phase rotation associated with the discontinuity is about 90 deg, lies in the same plane as the slowly rotaing part of the Alfven wave, and therefore completes the 360 deg phase rotation. The best description of the overall Alfven wave plus discontinuity is a spherical, arc-polarized, phase-steepened wave.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 21; 21; p. 2267-2270
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  • 2
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    The interplanetary magnetic field from 1 to 5 AU - Ulysses observations (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Observations of the IMF carried out from October 1990 to February 1992 during the in-ecliptic phase of the Ulysses mission are presented. The observations were made between 1 and 5.4 AU during a different phase of the solar cycle from previous missions. The large-scale reorganization of the solar coronal fields following the maximum in Solar Cycle 22 generated numerous transient events, causing large-scale disturbances in interplanetary space, particularly during the first half of 1991. From about the middle of 1991, solar activity apparently decreased, resulting in fewer transient events, allowing the formation of corotating interaction regions (CIRs) recurring in successive solar rotations. Observations of the IMF reflect this temporal evolution in solar activity. However, the average orientation of the IMF, the observed sector structure, and the evolution of the CIRs show that the dynamic interaction of transient events with evolving stream-stream structures in this heliocentric distance range results in significant deviations from the expected IMF topology, even when signature of the transients is less apparent.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 13; 6; p. 15-24.
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  • 3
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    The interaction of a very large interplanetary magnetic cloud with the magnetosphere and with cosmic rays (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The observation of one of the largest magnetic clouds ever observed at a distance of 1 AU, with a diameter of greater than about 0.4 AU, is reported. The cloud is shown to be almost unchanged structurally by interaction with the earth bow shock. The first observations are reported of an auroral activity response to the passage of a magnetic cloud, with a nearly immediate increase in auroral activity when the IMF theta(B) angle reversed polarity to negative near the cloud center. The results provide strong evidence that turbulent magnetic fields behind interplanetary shocks are a possible cause of Forbush decreases, but contest the idea that relatively smooth, strong fields in clouds are a cause of such decreases. The cloud field modeling supports the existence of magnetic force-free fields in describing cloud structure.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 9425-943
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  • 4
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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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  • 5
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    Cometary kilometric radio waves and plasma waves correlated with ion pick-up effect at Comet Halley (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Bow-shock movements at Comet Halley are inferred from the discrete spectra of the cometary kilometric radiation (30-195 kHz); the observed emissions can be interpreted as being generated and propagating from the moving shock. The shock motion is possibly associated with the time variation of the solar wind and cometary outgassing. It is concluded that these plasma wave phenomena are manifestations of ion pick-up processes, which occur even in a remote region 7 million to 10 million km from the cometary nucleus.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 5; 12, 1; 83-88
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  • 6
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    Discovery of cometary kilometric radiations and plasma waves at Comet Halley (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The plasma-wave probe carried by the spacecraft Sakigake discovered discrete spectra of emissions from Comet Halley in the frequency range 30-195 kHz. The observed cometary kilometric radiation appears to come from moving shocks in the coma region which are possibly associated with temporal variations of the solar wind. Waves due to plasma instabilities associated with the pick-up of cometary ions by the solar wind were observed within a region almost 10 million km from the comet nucleus.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 321; 307-310
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  • 7
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    The bow wave of Comet Giacobini-Zinner - ICE magnetic field observations (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Fitting of a Mach 2 shock surface to the ICE magnetic field data obtained near Comet Giacobini-Zinner has provided subsolar bow wave distances that infer neutral gas outflow rates comparable to previous measurements, and orientations of the bow wave symmetry axis that are consistent with the plasma measurements and motion of the comet relative to the solar wind. Mach values of 1.5-2 and transition thicknesses of the order of 10,000 km are inferred when the field magnitude and variance data are compared. Cross spectra of the transverse field components in and near the bow wave exhibit a peak near 0.01 Hz, or near the cyclotron frequency of ions from the water group. However, the level of turbulence is not consistent with that observed for similar configurations at planetary bow shocks.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 13; 243-246
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  • 8
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    Comet-solar wind interaction - Dynamical length scales and models (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: ICE magnetometer measurements at Comet Giacobini-Zinner and model simulations of comet-solar wind interactions are analyzed. The magnetometer data reveal the existence of intense hydromagnetic turbulence, a draping of the magnetic field lines to form a magnetotail, a weak shock, and a magnetic barrier region in the magnetosphere. The global models of the comet-solar wind interaction are described. The observed data and models are compared and good correlation is displayed.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 13; 239-242
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  • 9
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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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  • 10
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    Unusual characteristics of electromagnetic waves excited by cometary newborn ions with large perpendicular energies (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The characteristics of electromagnetic waves excited by cometary newborn ions with large perpendicular energies are examined using a model of solar wind permeated by dilute drifting ring distributions of electrons and oxygen ions with finite thermal spreads. The model has parameters compatible with the ICE observations at the Giacobini-Zinner comet. It is shown that cometary newborn ions with large perpendicular energies can excite a wave mode with rest frame frequencies in the order of the heavy ion cyclotron frequency, Omega(i), and unusual propagation characteristics at small obliquity angles. For parallel propagation, the mode is left-hand circularly polarized, might be unstable in a frequency range containing Omega(i), and moves in the direction of the newborn ion drift along the static magnetic field.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 187; 1-2,
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