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  • 1
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    ULF turbulence in the Neptunian polar cusp (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Results of a spectral analysis of the ULF wave turbulence in the Neptunian polar cusp are presented. The activity is characterized as broadbanded, extending up to a maximum frequency of about 0.5 Hz, and having maximum wave amplitudes as large as 6 percent of the dc magnetic field. Activity in the cusp region was particularly intense at its frontside and backside, associated with the magnetopause and cusp/magnetosphere boundaries, respectively. The turbulence, particularly that above f(ci), is tentatively identified as whistler mode. It is argued that such whistler mode turbulence should resonate with electrons having energies in the tens of kiloelectron volts. Observations indicate a very strong correlation of the ULF turbulence with the energetic electrons between 22 and 35 keV measured by Voyager's low-energy charged particle experiment. A vigorous interaction between the two is inferred. ULF wave turbulence in the cusp may represent a significant but not complete power source for the magnetosphere.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; A3; p. 3631-3643.
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  • 2
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    Large amplitude MHD waves upstream of the Jovian bow shock (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Observations of large amplitude MHD waves upstream of Jupiter's bow shock are analyzed. The waves are found to be right circularly polarized in the solar wind frame, which suggests that they are propagating in the fast magnetosonic mode. A complete spectral and minimum variance eigenvalue analysis of the data was performed. The power spectrum of the magnetic fluctuations contains several peaks. The fluctuations at 2.3 MHz have a direction of minimum variance anti-parallel to the direction of the average magnetic field. Several harmonics at 6, 9, and 12 MHz are also present. The direction of minimum variance of these fluctuations lies at approximately 40 deg to the magnetic field. It is argued that these fluctuations are waves excited by protons reflected off the Jovian bow shock. The inferred speed of the reflected protons is about two times the solar wind speed in the solar wind frame. A linear instability analysis is presented that suggests an explanation for many of the observed features of the observations. The fluctuations apparently contain a significant fraction of magnetic energy that is linearly polarized and in the Alfven mode.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 88; 9989-999
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  • 3
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    Large-amplitude MHD waves upstream of the Jovian bow shock Reinterpretation (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Observations of large amplitude magnetohydrodynamic (MHD) waves upstream of the Jovian bow shock were previously interpreted as arising from a resonant electromagnetic ion beam instability. That interpretation was based on the conclusion that the observed fluctuations were predominantly right elliptically polarized in the solar wind rest frame. Because it was noted that the fluctuations are, in fact, left elliptically polarized, a reanalysis of the observations was necessary. Several mechanisms for producing left hand polarized MHD waves in the observed frequency range were investigated. Instabilities excited by protons appear unlikely to account for the observations. A resonant instability excited by relativistic electrons escaping from the Jovian magnetosphere is a likely source of free energy consistent with the observations. Evidence for the existence of such a population of electrons was found in both the Low Energy Charged Particle experiments and Cosmic Ray experiments on Voyager 2.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 302-310
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  • 4
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    Turbulence analysis of the Jovian upstream 'wave' phenomenon (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: As Voyager 2 approached Jupiter's bow shock, large-amplitude fluctuations were seen in both the magnetic field and plasma fluid velocity. These fluctuations generally coincided with the occurrence of long-lived energetic particle events similar to the upstream waves often observed near the earth's bow shock. In this paper an analysis of the magnetic field and plasma observations using spectral methods is presented. The characteristic spectral features related to the upstream waves are generally seen near 1 mHz. The measured correlation lengths of these fluctuations suggest that they are coherent over only a few wavelengths. The analysis is consistent with the hypothesis that these fluctuations are driven by streaming ions, possibly protons. No evidence for the existence of whistler waves is found. It is argued that some of the observed spectral features suggest that dynamical turbulent processes are occurring in the uptream wave region, including a possible observation of an inverse cascade of magnetic helicity to large spatial scales.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 88; July 1
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  • 5
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    Large amplitude MHD waves upstream of the Jovian bow shock: Reinterpretation (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Observations of large amplitude magnetohydrodynamic (MHD) waves upstream of the Jovian bow shock were previously interpreted as arising from a resonant electromagnetic ion beam instability. That interpretation was based on the conclusion that the observed fluctuations were predominantly right elliptically polarized in the solar wind rest frame. Because it was noted that the fluctuations are, in fact, left elliptically polarized, a reanalysis of the observations was necessary. Several mechanisms for producing left hand polarized MHD waves in the observed frequency range were investigated. Instabilities excited by protons appear unlikely to account for the observations. A resonant instability excited by relativistic electrons escaping from the Jovian magnetosphere is a likely source of free energy consistent with the observations. Evidence for the existence of such a population of electrons was found in both the Low Energy Charged Particle experiments and Cosmic Ray experiments on Voyager 2.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-TM-86131 , NAS 1.15:86131
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  • 6
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    Large amplitude MHD waves upstream of the Jovian bow shock (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Observations of large amplitude magnetohydrodynamics (MHD) waves upstream of Jupiter's bow shock are analyzed. The waves are found to be right circularly polarized in the solar wind frame which suggests that they are propagating in the fast magnetosonic mode. A complete spectral and minimum variance eigenvalue analysis of the data was performed. The power spectrum of the magnetic fluctuations contains several peaks. The fluctuations at 2.3 mHz have a direction of minimum variance along the direction of the average magnetic field. The direction of minimum variance of these fluctuations lies at approximately 40 deg. to the magnetic field and is parallel to the radial direction. We argue that these fluctuations are waves excited by protons reflected off the Jovian bow shock. The inferred speed of the reflected protons is about two times the solar wind speed in the plasma rest frame. A linear instability analysis is presented which suggests an explanation for many of the observed features of the observations.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-TM-85005 , NAS 1.15:85005
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  • 7
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    Upstream waves at Uranus (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Since the Mach number of the solar wind increases with increasing heliocentric distance, the ratio of thermal to magnetic pressure, or beta, of the Uranian magnetosheath is expected to be much higher than in the terrestrial magnetosheath. Consistent with this expectation, the magnetosheat is observed to be extremely turbulent, and many particles may leak back upstream into the solar wind and/or be scattered from the bow shock. In accord with the expected presence of backstreaming particles, waves of the type associated with terrestrial backstreaming particles are seen outbound along the trajectory of Voyager in the preshock solar wind with frequencies close to 0.001 Hz. The wave frequency is close to that expected for upstream waves based on measurements closer to the sun. Upstream from the bow shock, the magnetic field was found to be much weaker than expected from observations in the inner solar system. The cause of this depression is unlikely to be the upstream particles; rather, the cause is probably intrinsic to the solar wind such as reconnection across the heliospheric current sheet.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 2273-227
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