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  • Space Radiation  (4)
  • SPACE RADIATION  (1)
  • 1
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    Source location determination of Uranian kilometric radiation from ray tracing and emission lobe modelling (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: We use an analytical fit to an emission lobe profile together with three-dimensional ray tracing to model the broad-banded smooth Uranian kilometric radiation (UKR). We assume the radiation is gyroemission from sources along magnetic field lines. Using an iterative technique that modifies the lobe function and source region, the results are compared to observations at a frequency of 481 kHz. The best-fit calculations are compared to previously published models and to recent ultraviolet (UV) observations.
    Keywords: SPACE RADIATION
    Type: NASA-CR-190482 , JPL-9950-1369 , NAS 1.26:190482
    Format: application/pdf
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  • 2
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    Radio Emissions Observed by Galileo near Io (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The Galileo spacecraft observed spin modulation of radio wave emissions near Io in the frequency range from about 600 kHz to about 1.2 MHz. Assuming transverse EM radiation, we have used the modulation of the high-frequency sweep-frequency receiver signals of the electric dipole antenna over many spins to estimate the plane through the source. The emission has a range of frequencies close to the local upper hybrid frequency of the plasma near Io. We conclude that the emission may be associated with either the plasma torus or magnetic flux tubes in the wake of Io (the Alfven current system). We postulate this emission may be associated with a free-energy source such as density gradients, energetic plasma beams and/or an electron distribution with a temperature anisotropy. All of these free-energy sources are observed or expected in the torus near Io. The observations are the first in the hectometric frequency range that have a source associated with Io or in the Io torus.
    Keywords: Space Radiation
    Type: Paper-97GL03442 , Geophysical Research Letters (ISSN 0094-8534); 25; 1; 25-28
    Format: text
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  • 3
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    Local Time Dependence of Jovian Radio Emissions Observed by Galileo (1999)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Galileo has been in orbit around Jupiter since December 1995. All the orbits are equatorial and elliptical, with apogees between 60 R(sub J) - 142 R(sub J) and perigees from 8 - 12 R(sub J). Since orbit injection, the plasma wave instrument (PWS) has been collecting data over specific intervals of each of the orbits at all local times and a range of different radial distances. We present the results of a survey of the data for the frequency range 300 kHz to 5.6 MHz, which includes the hectometric (HOM) and low-frequency decametric (DAM) emissions. The results indicate that both the HOM and DAM emission are more intense and occur more frequently in the midnight sector of Jupiter. This is in analogy to Earth and consistent with a magnetic substorm source for a portion of the radio emissions in this frequency range. Another peak in the power levels is observed on the Jovian dayside in the local time range 11 hrs 〈 LT 〈 12 hrs. This peak does not have a terrestrial counterpart. We speculate that this dayside peak may be a result of sampling near perigee, but we cannot rule out the possibility that this is not the case.
    Keywords: Space Radiation
    Type: Paper-1999GL900047 , Geophysical Research Letters (ISSN 0094-8276); 26; 5; 569-572
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  • 4
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    A High-Resolution Study of Quasiperiodic Radio Emissions Observed by the Galileo Plasma Wave Instrument (2001)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We have conducted a study of quasiperiodic emission observed by the plasma wave instrument on board the Galileo spacecraft. These emissions appear as broadband bursts with dominant periods ranging from 10 min to over 40 min. For these emissions we have explicitly analyzed the high-resolution (waveform) data to determine the presence of impulsive, solitary signatures. Our investigations have indicated that the broadband bursts, as well as the background more narrowband continuum emission, are composed of a highly turbulent spectrum. Within the broadband burst, however, there are higher-frequency components present, but no impulsive electrostatic signatures. Also significantly, the broadband bursts show no low-frequency dispersion. We conclude that the bursts are consistent with a distant, electromagnetic source, probably in the near-Jupiter vicinity.
    Keywords: Space Radiation
    Type: Paper-2000RS002570 , Radio Science (ISSN 0048-6604); 36; 4; 815-824
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  • 5
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    The Influence of The Galilean Satellites on Radio Emissions From The Jovian System (2000)
    In:  Other Sources
    Details
    Publication Date: 2019-07-10
    Description: The Galilean satellites influence radio emissions from the Jovian system in a variety of ways. The best and most familiar example of these is the Io control of decametric radiation discovered in 1964 by Bigg. Voyager observations of broadband kilometric radiation revealed a low-latitude shadow zone cast by the Io torus at frequencies between a few tens of kHz and about 1 MHz. Voyager also discovered narrowband kilometric radio emissions emanating from the outer edge of the torus. In this paper we will discuss expansions in the suite of satellite influences based on new observations by Galileo. These include the discovery of Ganymede's magnetosphere and evidence of radio emissions generated via mode conversion from upper hybrid waves in the frequency range of about 20 - 100 kHz. There is evidence that Ganymede may control some of the hectometric or low-frequency decametric radio emissions based on occultation measurements and statistical studies of radio emission occurrence as a function of Ganymede phase. Direction-finding measurements in the vicinity of Io suggest that a portion of the hectometric emissions may be generated near the lo L-shell. A rotationally modulated attenuation band in the hectometric emission appears to be the result of scattering at or near the Io L-shell where the waves propagate nearly parallel to the magnetic field. There is even a tantalizing hint of a Europa connection to the source of narrowband kilometric radiation.
    Keywords: Space Radiation
    Type: Geophysical-Monograph-119 , Radio Astronomy at Long Wavelenghts; 213-225
    Format: text
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