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  • 1
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    Observational study of the IMF spiral north and south of the current sheet (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: We have analyzed 23 years of spacecraft observations spanning 27 AU. Our analysis reveals both an overwinding of the interplanetary magnetic field (IMF) and a sustained asymmetry between the northern and southern hemispheres of the heliosphere. Nonzero azimuthal field components at the source boundary may account for the observed overwinding. The north-south asymmetry, whereby the IMF spiral north of the current sheet is more tightly wound than the IMF spiral south of the current sheet, persists due to unknown sources. It is also shown that there exist significant, correlated departures from the Parker theory in the azimuthal component of the field.
    Keywords: ASTROPHYSICS
    Type: In: Solar Wind Seven; Proceedings of the 3rd COSPAR Colloquium, Goslar, Germany, Sept. 16-20, 1991 (A93-33554 13-92); p. 273-276.
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Ion cyclotron harmonic resonances driven by ion ring-beam distributions (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Enhanced magnetic fluctuations with frequencies peaking at the ion cyclotron frequency and its harmonics have been observed at Comet Halley and also in the upstream regions of planetary bow shocks. It is thought that these waves are generated at comets by pickup ions that are unstable to the generation of waves at harmonics of the ion cyclotron wave number. In the spacecraft frame of reference these waves are observed as harmonics of the ion cyclotron frequency. In this report, it is shown that the ring-beam distributions of pickup ions observed in the cometary environment are capable of generating these waves if the beam speed component of the distribution (parallel to the ambient magnetic field) is much larger than the ring speed (perpendicular to the magnetic field). As the ring speed increases relative to the beam speed, other instabilities occur at the same wave number which have even larger growth rates. These additional instabilities do not lead to generation of harmonics.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 285-288
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Coupled hydromagnetic wave excitation and ion acceleration upstream of the Jovian bow shock (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: We extend the Lee (1982) self-consistent theory of upstream wave excitation and particle energization to address observations by Voyager 2 of sunward propagating MHD waves and diffuse suprathermal particle populations upstream of the Jovian bow shock. Two new ideas are incorporated into the theory. First, the interplanetary seed wave population is taken to be an equal admixture of waves propagating both toward and away from the shock parallel to the interplanetary magnetic field. Second, finite connection times are incorporated approximately into the theory in an effort to understand whether the particle spectra at high energy are limited by particle escape or finite connection time. It is found that finite connection times dominate the particle distribution at energies above 40 keV. In this manner the suprathermal proton distributions can be accounted for by a multiple reflection, shock acceleration theory. We find that the theory can also account for the low-frequency waves observed upstream of the shock in conjunction with the suprathermal ions.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 81-90
    Format: text
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    NASA TECHNICAL REPORTS
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