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- Menietti, J. D., et al.
(author)
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Analysis of Intense Z-Mode Emission Observed During the Cassini Proximal Orbits
- 2018
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 45:14, s. 6766-6772
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Journal article (peer-reviewed)abstract
- The role of Z-mode emission in the diffusive scattering and resonant acceleration of electrons is believed to be important at Saturn. A survey of the 5kHz component of this emission at Saturn earlier reported strong intensity in the lower density regions where the ratio of plasma frequency to cyclotron frequency, f(p)/f(c)<1. At Saturn this occurs along the inner edge of the Enceladus torus near the equator and at higher latitudes. Using the Cassini Radio and Plasma Wave Science instrument observations during the Cassini proximal orbits, we have now identified these emissions extending down to and within the ionosphere. Wave polarization measurements and unique frequency cutoffs are used to positively identify the wave mode. Analogous to the role of whistler mode chorus at Earth, Saturn Z-mode emissions may interact with electrons contributing to the filling or depleting of Saturn's inner radiation belts.
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| 3. |
- Menietti, J. D., et al.
(author)
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Extended Survey of Saturn Z-Mode Wave Intensity Through Cassini's Final Orbits
- 2018
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In: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 45:15, s. 7330-7336
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Journal article (peer-reviewed)abstract
- Similar to whistler mode chorus, Z-mode emission is an efficient diffusive scatterer of electrons possibly resulting in resonant acceleration. We present results of a survey of both the low-band (5 kHz) and for the first time the high-band (20 kHz) intensity of these emissions, based on over 11 years of Cassini Radio and Plasma Wave Science instrument data including nine ring-grazing orbits and two proximal orbits, which occurred at the end of the mission. We distinguish these emissions using density and polarization measurements and calculate the mean intensity as a function of frequency and spatial coordinates. We find that the average low-band Z-mode intensity peak is P-0 similar to 7 x 10(-8) nT(2), while the high-band peak is much lower at P-0 similar to 10(-9) nT(2). The spatial distribution of intensity differs for each emission band implying different source regions and perhaps different source mechanisms.Plain Language SummaryIntense narrow band waves (Z-mode) are observed at Saturn when the spacecraft is located in regions of relatively low density and high magnetic field. These waves are of special importance because they are not seen at such high intensity or over as large a spatial range at Earth. In addition, these waves are known to be very efficient at accelerating electrons under certain conditions and could be responsible for a portion of the observed radiation belts at Saturn. We present an extensive survey of the observations of Z-mode extending over more than 11 years. The survey includes for the first time both the low and high-frequency emissions and orbits from the Cassini final mission, where these waves were seen at a high rate of occurrence. Contour plots and graphs of wave intensity as a function of radius, latitude, and longitude are shown, which will be of value to scientists who model the dynamic processes controlling the electron population at Saturn.
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| 4. |
- Menietti, J. D., et al.
(author)
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Survey of Saturn Z-mode emission
- 2015
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In: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 120:8, s. 6176-6187
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Journal article (peer-reviewed)abstract
- Because of the role of Z-mode emission in the diffusive scattering and resonant acceleration of electrons, we conduct a survey of intensity in the Saturn inner magnetosphere. Z mode is primarily observed as 5kHz narrowband emission in the lower density regions where the ratio of cyclotron to plasma frequency, f(c)/f(p)>1 to which we limit this study. This occurs at Saturn along the inner edge of the Enceladus torus near the equator and at higher latitudes. We present profiles and parametric fits of intensity as a function of frequency, radius, latitude, and local time. The magnetic field intensity levels are lower than chorus, but the electric field intensities are comparable. We conclude that Z-mode wave-particle interactions may make a significant contribution to electron acceleration in the inner magnetosphere of Saturn, supplementing acceleration produced by chorus emission.
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| 5. |
- Ye, S. -Y, et al.
(author)
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Electron density inside Enceladus plume inferred from plasma oscillations excited by dust impacts
- 2014
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In: Journal of Geophysical Research-Space Physics. - 2169-9380. ; 119:5, s. 3373-3380
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Journal article (peer-reviewed)abstract
- Enceladus' southern plume is one of the major discoveries of the Cassini mission. The water neutrals and water ice particles (dust) ejected by the cryovolcanic activity populate Saturn's E ring and the neutral torus, and they interact with the plasma environment of Saturn's magnetosphere. The plasma neutrality inside Enceladus' plume has been shown by the Langmuir probe measurement to be modified by the presence of the dust particles. We present an independent method of determining the electron density inside the plume. Sometimes, after dust impacts, plasma oscillations (ringing) were detected by the Cassini Radio and Plasma Wave Science instrument. The frequencies of these oscillations have been shown to be consistent with the local plasma frequency, thus providing a measurement of the local electron density.
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