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  • 1
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    Plasma fluctuations and large-scale mixing near Comet Giacobini-Zinner (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The relationship among plasma densities, flow speeds and directions, and temperatures, at distances within about 100,000 km of Comet Giacobini-Zinner's nucleus, are presently examined in view of lowpass-filtered data from the International Cometary Explorer's electron spectrometer. While the largest amplitude density spikes often have more significant flow changes associated with them, a consistent pattern is not found. Power spectral analyses in and near the sheath/transition regions show that density fluctuation levels are enhanced at all detectable frequencies, consistent with strong density fluctuations on all time scales. Such mechanisms as the amplification of convected ion pickup waves and cometary rays for producing the large plasma variations are discussed. It is suggested that the Rayleigh-Taylor effect-driven mixing mechanism at a mass-loading boundary abut 100,000 km from the nucleus may be operative.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 13; 271-274
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  • 2
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    Energetic-ion acceleration and transport in the upstream region of Jupiter: Voyager 1 and 2 (1982)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Long-lived upstream energetic ion events at Jupiter appear to be very similar in nearly all respects to upstream ion events at Earth. A notable difference between the two planetary systems is the enhanced heavy ion compositional signature reported for the Jovian events. This compositional feature has suggested that ions escaping from the Jovian magnetosphere play an important role in forming upstream ion populations at Jupiter. In contrast, models of energetic upstream ions at Earth emphasize in situ acceleration of reflected solar wind ions within the upstream region itself. Using Voyager 1 and 2 energetic ( approximately 30 keV) ion measurements near the magnetopause, in the magnetosheath, and immediately upstream of the bow shock, the compositional patterns are examined together with typical energy spectra in each of these regions. A model involving upstream Fermi acceleration early in events and emphasizing energetic particle escape in the prenoon part of the Jovian magnetosphere late in events is presented to explain many of the features in the upstream region of Jupiter.
    Keywords: ASTROPHYSICS
    Type: NASA-TM-85179 , NAS 1.15:85179 , DE82-019574 , LA-UR-82-1914 , CONF-82058-3 , Symp. on Giant Planets and Their Satellites; May 17, 1982 - May 27, 1982; Ottawa
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  • 3
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    Relativistic electrons at geosynchronous orbit, interplanetary electron flux, and the 13-month Jovian synodic year (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Results are reported from a search to determine the correlation, if any, between the temporal behaviors of 0.2-7 MeV or higher electrons at GEO (6.6 earth radii) and 6-10 MeV electrons in the interplanetary region near earth at the period of the Jovian synodic year (about 13 months). The 13-month intensity variation results from the synodic interplanetary magnetic field conection of earth to Jupiter. Direct compariosn of intensity-time flux profiles for the years 1976-1984, about 7 synodic Jovian electron seasons, shows that the intensity envelope of peak electron flux at GEO does not appear to be correlated to the observed 13 month intensity envelope of relativistic electron flux in the interplanetary region near earth. A persistent 13-month variation of GEO flux is not obvious, thus indicating that the intensity of electron flux at GEO is not directly and soley related to the intensity of Jovian electron flux near earth. It is concluded that dynamic erergization and redistribution processes in earth's magnetosphere must be invoked to produce the intensity variations of relativistic electron flux at GEO and not interplanetary magnetic field connection to Jupiter.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 16; 1129-113
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  • 4
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    The collective emission of electromagnetic waves from astrophysical jets - Luminosity gaps, BL Lacertae objects, and efficient energy transport (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A model of the inner portions of astrophysical jets is constructed in which a relativistic electron beam is injected from the central engine into the jet plasma. This beam drives electrostatic plasma wave turbulence, which leads to the collective emission of electromagnetic waves. The emitted waves are beamed in the direction of the jet axis, so that end-on viewing of the jet yields an extremely bright source (BL Lacertae object). The relativistic electron beam may also drive long-wavelength electromagnetic plasma instabilities (firehose and Kelvin-Helmholtz) that jumble the jet magnetic field lines. After a sufficient distance from the core source, these instabilities will cause the beamed emission to point in random directions and the jet emission can then be observed from any direction relative to the jet axis. This combination of effects may lead to the gap turn-on of astrophysical jets. The collective emission model leads to different estimates for energy transport and the interpretation of radio spectra than the conventional incoherent synchrotron theory.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 326; 110-124
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  • 5
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    An examination of possible solar wind sources for a sudden brightening of Comet IRAS-Araki-Alcock (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Terrestrial and near-earth measurements are examined in order to investigate possible solar wind sources for the sudden global brightenings noted in Comet IRAS-Araki-Alcock. These brightenings are not found to be associated with increases in the solar wind momentum flux, quantity of solar energetic particles, or solar activity, in contradiction to the proposal of Lutz and Wagner (1986). If a radial alignment of the IMF seen at IMP-8 after about 0800 UT was not responsible for the cometary brightening, then it is suggested that the brightening must have been intrinsic to the comet.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 14; 991-994
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  • 6
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    Three component plasma electron distribution in the intermediate ionized coma of Comet Giacobini-Zinner (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The observation of three distinct components of the electron distribution function measured in the intermediate ionized coma (IIC) and plasma tail of Comet Giacobini-Zinner is reported. It is believed that the cold component represents electrons produced close to the comet nucleus by ionization of cometary matter and subsequent cooling by Coulomb collisions. The second component also appears to be composed of electrons produced by photoionization of cometary neutrals, but sufficiently far from the nucleus that the distributions are largely unaffected by Coulomb interactions. The hot component is probably a population of electrons originating in the solar wind. Throughout the IIC, the electrostatic potential of the spacecraft was very low (less than 0.8 eV), implying that ICE generated very little impact-produced plasma during its passage.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 13; 401-404
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