Observation of similar radio signatures at Saturn and Jupiter: Implications for the magnetospheric dynamics

Louarn, P.; Kurth, W. S.; Gurnett, D. A.; Hospodarsky, G. B.; Persoon, A. M.; Cecconi, Baptiste; Lecacheux, A.; Zarka, Philippe; Canu, P.; Roux, A.; Rücker, H. O.; Farrell, W. M.; Kaiser, M. L.; André, Nicolas; Harvey, C. C.; Blanc, Michel

doi:10.1029/2007gl030368

Cited by 45 publications

(51 citation statements)

References 28 publications

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“…(2) An intense but weakly circularly polarized emission shows up below 10 kHz. It has been named n-SMR (for narrowband Saturnian Myriametric Radiation) by Louarn et al [2007]. (3) In addition, we identify a third component in the range 10 -40 kHz, sometimes extending down to 3 kHz.…”

Section: Saturn's Low Frequency Radio Componentsmentioning

confidence: 99%

Saturn kilometric radiation: Average and statistical properties

et al. 2008

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Since Cassini entered Saturn's magnetosphere in July 2004, the auroral Saturnian kilometric radiation (SKR), which dominates the kronian radio spectrum, is observed quasi‐continuously. Consecutive orbits of the spacecraft covered distances to Saturn down to 1.3 Saturn radii, all local times and, since December 2006, latitudes as high as 60°. On the basis of carefully calibrated and cleaned long‐term time series and dynamic spectra, we analyze the average properties, and characteristics of the SKR over 2.75 years starting at Cassini's Saturn orbit insertion. This study confirms and expands previous results from Voyager 1 and 2 studies in the 1980s: the SKR spectrum is found to extend from a few kHz to 1200 kHz; extraordinary mode emission dominates, i.e., left‐handed (LH) from the southern kronian hemisphere and right‐handed (RH) from the northern one, for which we measure directly a degree of circular polarization up to 100%; the variable visibility of SKR along Cassini's orbit is consistent with sources at or close to the local electron cyclotron frequency fce, in the Local Time (LT) sector 09 h–12 h, and at latitudes ≥70°, with emission beamed along hollow cones centered on the local magnetic field vector; this anisotropic beaming results in the existence of an equatorial radio shadow zone, whose extent is quantified as a function of frequency; it also causes the systematic disappearance of emission at high latitudes above 200 kHz and below 30 kHz. In addition, we obtain new results on SKR: LH and RH intensity variations are found to match together at all timescales ≥30 min; moreover their spectra are found to be conjugated as a function of the latitude of the observer; we use this conjugacy to merge LH and RH spectra and derive pronounced systematic dependences of the SKR spectrum as a function of the spacecraft latitude and LT (that will be the input of a subsequent modeling study); we identify for the first time ordinary mode SKR emission; finally, in addition to the SKR and n‐SMR components, we discuss the narrowband kilometric component (named here n‐SKR) which extends mainly between 10 and 40 kHz, preferentially observed from high latitudes.

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Section: Saturn's Low Frequency Radio Componentsmentioning

confidence: 99%

Saturn kilometric radiation: Average and statistical properties

et al. 2008

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“…The lower cutoff of SKR is chosen to avoid the numerous observations of narrowband emission (see Introduction) at frequencies typically in the range 5 kHz-40 kHz (cf. Louarn et al, 2007;Lamy et al, 2008a;Ye et al, 2009). We evaluate the mean intensity over successive 1-min time intervals for the specified frequency range.…”

Section: Observationsmentioning

confidence: 99%

“…A peculiar feature of the Saturn SKR is that it appears to display clock-like periodicity with more intense emission occurring when a particular Saturn longitude is near the sub-solar point (Gurnett et al, 1981;Warwick et al, 1981). Kaiser et al (1981), Kaiser and Desch (1982), and Lecacheux and Genova (1983) have reported that the radio Correspondence to: J. D. Menietti (john-menietti@uiowa.edu) emission sources are in both hemispheres, with the strongest being the Northern Hemisphere. Using the original Saturn longitude system, SLS, the northern source appears to be confined to magnetic field lines with footprints in the range 70 • <latitude<80 • and 100 • <SLS<130 • , and the sources are strongest in the local time range 10:00 h<LT<12:00 h. The Southern Hemisphere source appears to be in the range −60 • <latitude< −85 • and 300 • to 75 • SLS, and strongest in the broader range 07:00 h<LT<16:00 h. These observations have never been completely explained, and due to the apparent drifting of the SLS system, it is important to determine how these observations may have changed.…”

Section: Introductionmentioning

confidence: 99%

The influence of Titan on Saturn kilometric radiation

Menietti

Piker

et al. 2010

Ann. Geophys.

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Abstract.Previous studies have shown that the occurrence probability of Saturn Kilometric Radiation (SKR) appears to be influenced by the local time of Titan. Using a more extensive set of data than the original study, we confirm the correlation of higher occurrence probability of SKR when Titan is located near local midnight. In addition, the direction finding capability of the Cassini Radio Plasma Wave instrument (RPWS) is used to determine if this radio emission emanates from particular source regions. We find that most source regions of SKR are located in the mid-morning sector of local time even when Titan is located near midnight. However, some emission does appear to have a source in the Saturnian nightside, consistent with electron precipitation from field lines that have recently mapped to near Titan.

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“…These emissions are most often characterized as narrow-banded at f <f ce /2 and/or f >f ce /2 with an emission gap near f ce /2. It is generally believed that chorus is generated by a nonlinear process based on the electron cyclotron resonance of whistler-mode waves with energetic electrons, taking place close to the geomagnetic equatorial plane (Omura et al, 1991;Nunn et al, 1997;LeDocq et al, 1998). Storm-time chorus is especially important for the physics of the Earth's magnetosphere since it can significantly influence the distribution functions of the energetic electrons in the outer radiation belt (e.g.…”

Section: Introductionmentioning

confidence: 99%

Analysis of plasma waves observed in the inner Saturn magnetosphere

et al. 2008

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Abstract. Plasma waves observed in the Saturn magnetosphere provide an indication of the plasma population present in the rotationally dominated inner magnetosphere. Electrostatic cyclotron emissions often with harmonics and whistler mode emission are a common feature of Saturn's inner magnetosphere. The electron observations for a region near 5 R S outside and near a plasma injection region indicate a cooler low-energy (<100 eV), nearly isotropic plasma, and a much warmer (E>1000 eV) more pancake or butterfly distribution. We model the electron plasma distributions to conduct a linear dispersion analysis of the wave modes. The results suggest that the electrostatic electron cyclotron emissions can be generated by phase space density gradients associated with a loss cone that may be up to 20 • wide. This loss cone is sometimes, but not always, observed because the field of view of the electron detectors does not include the magnetic field line at the time of the observations. The whistler mode emission can be generated by the pancake-like distribution and temperature anisotropy (T ⊥ /T || >1) of the warmer plasma population.

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Observation of similar radio signatures at Saturn and Jupiter: Implications for the magnetospheric dynamics

Cited by 45 publications

References 28 publications

Saturn kilometric radiation: Average and statistical properties

Saturn kilometric radiation: Average and statistical properties

The influence of Titan on Saturn kilometric radiation

Analysis of plasma waves observed in the inner Saturn magnetosphere

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