Radio Wave Emission from the Outer Planets Before Cassini

Zarka, Philippe; Kurth, W. S.

doi:10.1007/s11214-005-1962-2

Cited by 47 publications

(17 citation statements)

References 84 publications

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“…It is the most intense component of Saturn's low-frequency radio spectrum, covering the range between a few kHz and $1.3 MHz, with a maximum intensity between 100 and 400 kHz. Spectral structures such as arcs and bursts are visible in SKR dynamic spectra, although less organized than in the Jovian case (see reviews by Kurth and Zarka [2001] and Zarka and Kurth [2005]). Measured variations of the SKR polarization along the Voyager 1 and 2 flyby trajectories allowed Galopeau et al [1995] (hereafter G95) to constrain the northern and southern SKR source locations.…”

Section: Skr Source Location and Originmentioning

confidence: 99%

Model of a variable radio period for Saturn

Cecconi

Zarka

2005

J. Geophys. Res.

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We propose an explanation for the variations at the 1% level of Saturn's radio rotation period measured at kilometer wavelengths. Because Saturn's kilometric radiation (SKR) is strongly controlled by the solar wind, we suggest that nonrandom variations of solar wind characteristics, especially its velocity, at Saturn may result in systematic displacement of the auroral sources in local time and finally in modifications of the apparent radio period. Alternatively, it may result in the superposition of two apparent periods, as also observed in Voyager data. We develop two simple models of local time variations of the SKR sources and analyze the conditions under which the measured radio period may be shifted by up to a few percent from the planet's sidereal period. Our results provide a possible explanation for the 1% variation observed and suggest that the dominant peak in the harmonic analysis of SKR variations seen by Voyager may be different from Saturn's sidereal rotation period. We relate the limitation in the accuracy of planetary rotation period determination to long‐term variations of “control” parameters (like the solar wind velocity). One and a half to three years of continuous SKR observations with Cassini will be required to reliably and accurately derive Saturn's true sidereal period.

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Section: Skr Source Location and Originmentioning

confidence: 99%

Model of a variable radio period for Saturn

Cecconi

Zarka

2005

J. Geophys. Res.

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“…Subsequent observations revealed that all magnetized planets are radio sources (see review by Zarka and Kurth, 2005). Radio waves can travel far from their source region, carrying spectral signatures of the local conditions where they are generated.…”

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confidence: 99%

Remote sensing of a NTC radio source from a Cluster tilted spacecraft pair

Décréau¹,

Kougblénou²,

Lointier³

et al. 2013

Ann. Geophys.

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Abstract. The Cluster mission operated a "tilt campaign" during the month of May 2008. Two of the four identical Cluster spacecraft were placed at a close distance (∼ 50 km) from each other and the spin axis of one of the spacecraft pair was tilted by an angle of ∼ 46 • . This gave the opportunity, for the first time in space, to measure global characteristics of AC electric field, at the sensitivity available with long boom (88 m) antennas, simultaneously from the specific configuration of the tilted pair of satellites and from the available base of three satellites placed at a large characteristic separation (∼ 1 R E ). This paper describes how global characteristics of radio waves, in this case the configuration of the electric field polarization ellipse in 3-D-space, are identified from in situ measurements of spin modulation features by the tilted pair, validating a novel experimental concept. In the event selected for analysis, non-thermal continuum (NTC) waves in the 15-25 kHz frequency range are observed from the Cluster constellation placed above the polar cap. The observed intensity variations with spin angle are those of plane waves, with an electric field polarization close to circular, at an ellipticity ratio e = 0.87. We derive the source position in 3-D by two different methods. The first one uses ray path orientation (measured by the tilted pair) combined with spectral signature of magnetic field magnitude at source. The second one is obtained via triangulation from the three spacecraft baseline, using estimation of directivity angles under assumption of circular polarization. The two results are not compatible, placing sources widely apart. We present a general study of the level of systematic errors due to the assumption of circular polarization, linked to the second approach, and show how this approach can lead to poor triangulation and wrong source positioning. The estimation derived from the first method places the NTC source region in the dawn sector, at a large L value (L ∼ 10) and a medium geomagnetic latitude (35 • S). We discuss these untypical results within the frame of the geophysical conditions prevailing that day, i.e. a particularly quiet long time interval, followed by a short increase of magnetic activity.

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“…e.g. Treumann, 2006) for the electroncyclotron maser to work, is a perpendicular velocity gradient on the electron phase space distribution function and the presence of mildly relativistic electrons in resonance (known since the seminal work of Wu and Lee, 1979). Again, this latter point is crucial.…”

Section: Downward Current Region Electron Holesmentioning

confidence: 99%

“…e.g. Zarka and Kurth, 2005;Hess et al, 2009;Louarn et al, 2007;Mottez et al, 2010;Treumann et al, 2011b;Bykov and Treumann, 2011, and references therein). Radiation that would be generated outside the electron hole in the perpendicular velocity gradient between the hole and the fast accelerated beam or between the beam and the background distribution will not experience amplification.…”

Section: Amplificationmentioning

confidence: 99%

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Electron-cylotron maser radiation from electron holes: downward current region

2012

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Abstract. The electron-cyclotron maser emission theory from electron holes is applied to holes generated in the downward current region of the aurora. It is argued that the main background auroral kilometric radiation source may still be located in the upward current region electron-ring (horseshoe) distribution while the fine structure is caused by electron holes predominantly in the downward current region. There the existence of electron holes is well established and electron densities are high enough for substantial maser growth rates. Trapping of radiation by the holes provides strong amplification. Upward motion of holes favours the escape of radiation both, from the holes and from the downward current region, into the upward current region. Since upward and downward current regions always exist simultaneously, they are acting in tandem in generating auroral kilometric radiation and its fine structure by the same mechanism though in different ways. This mechanism solves the longstanding problem of auroral kilometric radiation fine structure.

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Radio Wave Emission from the Outer Planets Before Cassini

Cited by 47 publications

References 84 publications

Model of a variable radio period for Saturn

Model of a variable radio period for Saturn

Remote sensing of a NTC radio source from a Cluster tilted spacecraft pair

Electron-cylotron maser radiation from electron holes: downward current region

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