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  • 11
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    Latitudinal beaming of Jupiter's low frequency radio emissions (1979)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Observations of Jupiter's radio emissions from Jovigraphic latitudes greater than 3.3 deg are reported. The measurements were obtained from the Voyager 2 spacecraft at declinations up to 6.5 deg, and when these results are compared with simultaneous observations from Voyager 1 near the ecliptic plane (at a Jovigraphic latitude of about 3 deg), they indicate that the latitudinal-beaming effects persist and may even become stronger with higher latitudes. The results were combined with earlier low-frequency measurements from periods with De as low as -3 deg in order to show the beaming effects the occurrence of the emission over a full 10 deg range of altitude. The results of observations at frequencies near 1 MHz are also discussed, which were obtained from Voyager 1 and 2 in 1978, Rae 1 in 1969, and Imp 6 in 1971-1972. The implications of the new results for models of Jupiter's radio-emission beam pattern are considered.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 84; Sept. 1
    Format: text
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  • 12
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    A beaming model of the Io-independent Jovian decameter radiation based on multipole models of the Jovian magnetic field (1979)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: A geometrical model is presented in which the apparent source locations of the Io-independent decameter radiation are computed. The calculations assume that the radiation is produced by stably trapped electrons radiating near the local electron gyrofrequency and that the emission is then beamed onto a conical surface. The maximum occurrence probability of noise storms is associated with regions in the Jovian magnetosphere where the axis of the emission cone is most inclined toward the Jovian equatorial plane. The calculations utilize and compare two of the octopole spherical harmonic expansions of the Jovian magnetic field constructed from data accumulated by the fluxgate and vector helium magnetometers on board Pioneer 11.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal; vol. 229
    Format: text
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  • 13
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    Master data directories and Catalog Interoperability (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: While the 'Catalog Interoperability' (CI) project began as a NASA effort to facilitate identification, location, and access to data of interest to space and earth sciences researchers, it now has a membership encompassing numerous U.S. and international agencies as well as academic institutions. CI is creating a global network of interconnected directory, catalog, and inventory systems. Its directories contain brief summary information about data sets, and can either furnish automated links to other information systems yielding greater detail on matters of interest or indicate to whom requests for additional information can go.
    Keywords: DOCUMENTATION AND INFORMATION SCIENCE
    Type: AIAA PAPER 90-5062
    Format: text
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  • 14
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    The formation of arcs in the dynamic spectra of Jovian decameter bursts (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A model is presented that can account for several features of the dynamic spectral arcs observed at decameter wavelengths by the planetary radio astronomy experiment on Voyagers 1 and 2. It is shown that refraction of an extraordinary mode wave initially excited nearly orthogonal to the local magnetic field is significantly influenced by the local plasma density, being greater the higher the density. It is assumed that the source of the decameter radiation lies along the L = 6 flux tube and that the highest frequencies are produced at the lowest altitudes, where both the plasma density and magnetic field gradients are largest. It is further assumed that the decameter radiation is emitted into a thin conical sheet, consistent with both observation and theory. In the model the emission cone angle of the sheet is chosen to vary with frequency so that it is relatively small at both high and low frequencies, but approximately 80 deg at intermediate frequencies. The resulting emission pattern as seen by a distant observer is shown to resemble the observed arc pattern. The model is compared and contrasted with examples of Voyager radio data.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-TM-81987
    Format: application/pdf
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  • 15
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    Arcs in Saturn's radio spectra (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Arcs appearing in the dynamic spectra of Saturn radio emission have been modelled using the same techniques as applied to Jovian arcs. Their properties suggest a source region several tenths of a Saturn radius above the cloud tops in the late morning local time sector.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 292; Aug. 20
    Format: text
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  • 16
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    Decameter-wave radio observations of Jupiter during the 1977 apparition (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A catalog of observations of Jupiter's sporadic decameter wavelength radio emissions obtained with the Goddard Space Flight Center Jupiter Monitor Network between June 1977 and May 1978 is presented. Data were collected using the Goddard Space Flight Center station in Greenbelt, MD. and at facilities installed at Orroral Valley (Canberra), Australia and the Nancay Radio Observatory in France. Observations were obtained daily at frequencies of 16.7 and 22.2 MHz using five-element Yagi antennas at each end of a two-element interferometer. Plots of the two dimensional emission occurrence probability distribution are given.
    Keywords: ASTRONOMY
    Type: NASA-TM-84012 , X-695-78-25
    Format: application/pdf
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  • 17
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    Planetary radio astronomy observations from Voyager 2 near Jupiter (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The Voyager 2 Planetary Radio Astronomy experiment to Jupiter has confirmed and extended to higher zenomagnetic latitudes results from the identical experiment carried by Voyager 1. The kilometric emissions discovered by Voyager 1 often extended to 1 megahertz or higher on Voyager 2 and often consisted of negatively, or less frequently, positively drifting narrowband bursts. On the basis of tentative identification of plasma wave emissions similar to those detected by Voyager 1, the plasma torus associated with Io appeared somewhat denser to Voyager 2 than it did to Voyager 1. The paper reports on quasi-periodic sinusoidal or impulsive bursts in the broadcast band range of wavelengths (800 to 1800 kHz). A Faraday effect appears at decametric frequencies, which probably results from propagation of the radiation near its sources on Jupiter. Finally, the occurrence of decametric emission in homologous arc families is discussed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 206; Nov. 23
    Format: text
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  • 18
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    Synoptic observations of Jupiter's radio emissions: Average Statistical properties observed by Voyager (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Observations of Jupiter's low frequency radio emissions collected over one month intervals before and after each Voyager encounter were analyzed. Compilations of occurrence probability, average power flux density and average sense of circular polarization are presented as a function of central meridian longitude, phase of Io, and frequency. The results are compared with ground based observations. The necessary geometrical conditions are preferred polarization sense for Io-related decametric emission observed by Voyager from above both the dayside and nightside hemispheres are found to be essentially the same as are observed in Earth based studies. On the other hand, there is a clear local time dependence in the Io-independent decametric emission. Io appears to have an influence on average flux density of the emission down to below 2 MHz. The average power flux density spectrum of Jupiter's emission has a broad peak near 9MHz. Integration of the average spectrum over all frequencies gives a total radiated power for an isotropic source of 4 x 10 to the 11th power W.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-TM-80717
    Format: application/pdf
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  • 19
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    The formation of arcs in the dynamic spectra of Jovian decameter bursts (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A model is presented that accounts for several features of the dynamic spectral arcs observed at decameter wavelengths by the planetary radio astronomy experiment on Voyagers 1 and 2. It is shown that refraction of an extraordinary mode wave initially excited and nearly orthogonal to the local magnetic field is significantly influenced by the local plasma density. The source of the radiation is on the L = 6 flux, and the emission cone angle of the sheet is chosen to vary with frequency so that it is relatively small at both high and low frequencies while about 80 deg at intermediate frequencies. This functional dependence of cone angle on frequency appears to be consistent with estimates of refraction of the ordinary mode in a source region where the electron density is greater than a few hundred per cu cm.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Sept. 30
    Format: text
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  • 20
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    Synoptic observations of Jupiter's radio emissions - Average statistical properties observed by Voyager (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Observations of Jupiter's low-frequency radio emissions collected over one-month intervals before and after each Voyager encounter are analyzed to provide a synoptic view of the average statistical properties of the emissions. Compilations of occurrence probability, average power flux density, and average sense of circular polarization are given as a function of central meridian longitude, phase of Io, and frequency. The results are then compared with ground-based observations. The necessary geometric conditions and preferred polarization sense for Io-related decametric emission observed by Voyager from above both the dayside and nightside hemispheres are found to be basically the same as those observed in earth-based studies.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Sept. 30
    Format: text
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