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  • LUNAR AND PLANETARY EXPLORATION  (14)
  • 1
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    Modeling and investigative studies of Jovian low frequency emissions (1986)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: The Voyager data in a newly produced noise-reduced and recalibrated format has been received. New color spectrograms were developed on high resolution color terminals which display this data. The production of these new spectrograms utilizing the new format data is quite important, because it eliminates a serious problem of noise contamination and miscalibration in the old data set. In addition, a new Jovian plasma model was introduced, which includes the Io torus and accounts for 7 ionic species. The new plasma model is important in the ray tracing of hectometric (HOM) and kilometric (KOM) radiation which may be influenced by the Io torus.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington Reports of Planetary Astronomy, 1985; p 44-45
    Format: text
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  • 2
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    Modeling and investigative studies of Jovian low frequency emissions (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Jovian decametric (DAM) and hectometric (HOM) emissions were first observed over the entire spectrum by the Voyager 1 and 2 flybys of the planet. They display unusual arc-like structures on frequency-versus-time spectrograms. Software for the modeling of the Jovian plasma and magnetic field environment was performed. In addition, an extensive library of programs was developed for the retrieval of Voyager Planetary Radio Astronomy (PRA) data in both the high and low frequency bands from new noise-free, recalibrated data tapes. This software allows the option of retrieving data sorted with respect to particular sub-Io longitudes. This has proven to be invaluable in the analyses of the data. Graphics routines were also developed to display the data on color spectrograms.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-TM-89299 , NAS 1.15:89299
    Format: application/pdf
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  • 3
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    Whistler propagation in the Jovian magnetosphere (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The paper deals with computer ray tracing results for lightning-generated whistlers propagating in the Jovian magnetosphere. The waves are launched from a point on the Jovian surface at 66 degrees latitude and propagate approximately along L = 6 out to near the equatorial plane and into the Io plasma torus. The results clearly indicate that the whistlers propagate with very little dispersion until they reach the torus, at which time the dispersion starts to increase very rapidly. Good agreement between the computed and observed dispersions is established.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters; 7; Jan. 198
    Format: text
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  • 4
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    Jovian decametric arcs - An estimate of the required wave normal angles from three-dimensional ray tracing. (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Three-dimensional ray tracing is applied to an analysis of variable radio wave normal angle effects on the associated decametric (DAM) arc structures in the Jovian magnetosphere. The analysis is bed on 1-40 MHz radio signature recorded during Voyage 1 and 2 passages. The frequencies considered are above the R-X cut-off, and several ratios of the emission frequency/source frequency. The ray tracing code is based on a cold plasma formula and integration of the Hasselgrove (1955) equations. It is assumed that the emission is in the R-X mode, the source lies at the foot of an Io flux tube, and the emission cone is hollow. Attention is focused on data for two intense, vertex-late, high curvature DAM arc. A possible source for the arcs is found to be doppler-shifted gyroemission from a beam of electrons with an energy of 10 keV. A value of 1.1 is set as the limit of the doppler shift of the DAM emissions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 9089-909
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  • 5
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    Three-dimensional ray tracing of the Jovian magnetosphere in the low-frequency range (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Three-dimensional ray tracing of the Jovian DAM emission has been performed utilizing the O-4 magnetic field model (Acuna and Ness, 1979) and a realistic plasma model. Minimal assumptions about the emission mechanism have been made that include radiation in the right-hand extraordinary mode, propagating nearly perpendicular to the field line at source points located just above the RX cutoff frequency along Io flux tubes. Ray tracing has been performed in the frequency range from 2-35 MHz from successive Io flux tubes separated by ten degrees of central meridian longitude for a full circumference of northern hemisphere sources. The results show unusual complexity in model arc spectra that is displayed in a constant Io phase format with many similarities to the Voyager PRA data. The results suggest much of the variation in observed DAM spectral features is a result of propagation effects rather than emission process differences.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 1489-149
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  • 6
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    Three dimensional ray tracing Jovian magnetosphere in the low frequency range (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Ray tracing of the Jovian magnetosphere in the low frequency range (1+40 MHz) has resulted in a new understanding of the source mechanism for Io dependent decametric radiation (DAM). Our three dimensional ray tracing computer code has provided model DAM arcs at 10 deg. intervals of Io longitude source positions for the full 360 deg of Jovian system III longitude. In addition, particularly interesting arcs were singled out for detailed study and modelling. Dependent decametric radiation arcs are categorized according to curvature--the higher curvature arcs are apparently due to wave stimulation at a nonconstant wave normal angle, psi. The psi(f) relationship has a signature that is common to most of the higher curvature arcs. The low curvature arcs, on the other hand, are adequately modelled with a constant wave normal angle of close to 90 deg. These results imply that for higher curvature arcs observed for from Jupiter (to diminish spacecraft motion effects) the electrons providing the gyroemission are relativistically beamed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-170237 , JPL-9950-801 , NAS 1.26:170237
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  • 7
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    Three dimensional ray tracing of the Jovian magnetosphere in the low frequency range (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Ray tracing studies of Jovian low frequency emissions were studied. A comprehensive three-dimensional ray tracing computer code for examination of model Jovian decametric (DAM) emission was developed. The improvements to the computer code are outlined and described. The results of the ray tracings of Jovian emissions will be presented in summary form.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-175462 , JPL-9950-981 , NAS 1.26:175462
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  • 8
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    N-bursty emission from Uranus: A cyclotron maser source? (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Ray tracing studies of RX-mode emission from the north polar regions of Uranus indicate that the n-bursty radio emission may have a source along field lines with footprints near the northern magnetic pole (perhaps in the cusp), but not necessarily associated with regions of strong UV emission. This is in contrast with similar studies for the Uranus nightside smooth radio emission, which are believed to be due to the cyclotron maser instability. Source regions can be found for both hollow and filled emission cones and for frequencies well above the local gyrofreuquency implying that mechanisms other than the cyclotron maser mechanism may be operating.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 20; 22; p. 2439-2442
    Format: text
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  • 9
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    Possible second harmonic gyroemission at Uranus (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: During the inbound trajectory toward Uranus, the Planetary Radio Astronomy Instrument on board the Voyager 2 spacecraft observed narrow-band smooth (n-smooth) emission at frequencies centered near 60 kHz. By assuming models of the plasma density for the dayside magnetosphere of Uranus and by using cold plasma theory together with stringent observational constraints, ray-tracing calculations were performed to determine the source location and mode of the n-smooth emission. Ray-tracing calculations suggest that the n-smooth emission with sources near the magnetic equator may be fundamental X mode for certain conditions or second harmonic gyroemission. If the emission is second harmonic gyroemission, the fundamental emission at 30 kHz is expected but apparently not observed. These findings are discussed in the context of the most recent developments in the theory of the cyclotron maser instability.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 20959-20
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  • 10
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    Source region of the smooth high-frequency nightside Uranus kilometric radiation - A ray-tracing study (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: This paper presents a plasma density model for the Uranus nightside at r less than 4.2 r(u), developed on the basis of radio wave observations of the Planetary Radio Astronomy instrument on board the Voyager 2 spacecraft and on cyclotron maser instability. The results provide an accurate description of the Uranus kilometric radiation (UKR) source region dependent on a minimum of assumptions, and indicate that the UKR source region is more extended in longitude than previosly determined.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 51-60
    Format: text
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