The reversal of the rotational modulation rates of the north and south components of Saturn kilometric radiation near equinox

Gurnett, D. A.; Groene, J. B.; Persoon, A. M.; Menietti, J. D.; Ye, Shengyi; Kurth, W. S.; MacDowall, R. J.; Lecacheux, A.

doi:10.1029/2010gl045796

Cited by 67 publications

(122 citation statements)

References 22 publications

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“…The periods converged during 2009, but so far there is no consensus when the SKR periods crossed or coalesced. Gurnett et al (2010) suggested that the periods coalesced in spring 2010, similar to , who suggested a crossing of two very close periods around the same time in spring 2010. The question is related to the proper identification of northern and southern SKR, where the wave polarization and the spacecraft latitude can be used to separate northern from southern SKR intensities.…”

mentioning

confidence: 64%

“…Fischer et al (2014) suggested that northern and southern periods crossed in late August 2009, just a few weeks after Saturn equinox on 11 August 2009. Nevertheless, all authors (Gurnett et al, 2010;Fischer et al, 2014) agree that northern and southern periods are very similar (∼ 10.7 h) in spring 2010. In contrast to that, the periods of magnetic field oscillations of both hemispheres did not cross in the time interval studied until late 2012 .…”

mentioning

confidence: 86%

“…Two distinct warm airmasses in Saturn's stratosphere, located near 0.5 mbar around the GWS at 35 • north latitude, formed and intensified from January until April 2011, before they merged into one large hot spot in late April with a temperature 80 K higher than the quiescent surroundings . The tracking filter analysis of Gurnett et al (2009Gurnett et al ( , 2010Gurnett et al ( , 2011 employed in the last section uses sliding windows of 240 days and time steps of 30 days. To gain further insight into the SKR modulation during the GWS event, we simply follow the SKR phase as a function of time allowing us to see changes on shorter timescales.…”

Section: Detailed Behavior Of Skr Modulation During the Gws Eventmentioning

confidence: 99%

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A possible influence of the Great White Spot on Saturn kilometric radiation periodicity

Fischer

Groene

et al. 2014

Ann. Geophys.

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Abstract. The periodicity of Saturn kilometric radiation (SKR) varies with time, and its two periods during the first 5 years of the Cassini mission have been attributed to SKR from the northern and southern hemisphere. After Saturn equinox in August 2009, there were long intervals of time (March 2010 to February 2011 and September 2011 to June 2012) with similar northern and southern SKR periods and locked SKR phases. However, from March to August 2011 the SKR periods were split up again, and the phases were unlocked. In this time interval, the southern SKR period slowed down by ~ 0.5% on average, and there was a large jump back to a faster period in August 2011. The northern SKR period speeded up and coalesced again with the southern period in September 2011. We argue that this unusual behavior could be related to the so-called Great White Spot (GWS), a giant thunderstorm that raged in Saturn's atmosphere around that time. For several months in 2011, the visible head of the GWS had the same period of ~ 10.69 h as the main southern SKR modulation signal. The GWS was most likely a source of intense gravity waves that may have caused a global change in Saturn's thermospheric winds via energy and momentum deposition. This would support the theory that Saturn's magnetospheric periodicities are driven by the upper atmosphere. Since the GWS with simultaneous SKR periodicity measurements have only been made once, it is difficult to prove a physical connection between these two phenomena, but we provide plausible mechanisms by which the GWS might modify the SKR periods.

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confidence: 64%

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confidence: 86%

Section: Detailed Behavior Of Skr Modulation During the Gws Eventmentioning

confidence: 99%

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A possible influence of the Great White Spot on Saturn kilometric radiation periodicity

Fischer

Groene

et al. 2014

Ann. Geophys.

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“…It is now known that the SKR rotational modulation period is not only variable, but has two periods [Kurth et al, 2008], one at about 10.6 hr that originates primarily from a source in the northern auroral region, and the other at about 10.8 hr that originates primarily from a source in the southern auroral region [Gurnett et al, 2009a]. Recent Cassini data show that these two periods reversed a few months after the August 2009 equinox [Gurnett et al, 2010a;Lamy, 2011].…”

Section: Introductionmentioning

confidence: 99%

The rotation of the plasmapause-like boundary at high latitudes in Saturn's magnetosphere and its relation to the eccentric rotation of the northern and southern auroral ovals

Gurnett

Persoon

Groene

et al. 2011

Geophys. Res. Lett.

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Here we present a study of the rotation of the plasmapause‐like density boundary discovered by the Cassini spacecraft at high latitudes in the Saturnian magnetosphere, and compare the results with previously published studies of high‐latitude magnetic field perturbations and the eccentric rotation of the auroral ovals. Near the planet the density boundary is located at dipole L values ranging from about 8 to 15, and separates a region of very low densities at high latitudes from a region of higher densities at lower latitudes. We show that the density boundary rotates at different rates in the northern and southern hemispheres, and that the periods are the same as the modulation periods of Saturn kilometric radiation in those hemispheres. We also show that the phase of rotation in a given hemisphere is closely correlated with the phase of the high‐latitude magnetic field perturbations observed by Cassini in that hemisphere, and also with the phase of the eccentric rotation of the auroral oval observed by the Hubble Space Telescope.

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“…Note the crossing of the first (south) and second (north) SKR component several months after equinox. a series of detailed investigations Gurnett et al, 2010;Lamy, 2011). The most intriguing fact is the appearance of a second component of SKR observed in the northern hemisphere of Saturn with a significantly different rotational periodicity (Fig.…”

Section: Saturn Radio Emission Periodicitymentioning

confidence: 99%

Planetary radio astronomy: Earth, giant planets, and beyond

2014

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Abstract. The magnetospheric phenomenon of non-thermal radio emission is known since the serendipitous discovery of Jupiter as radio planet in 1955, opening the new field of "Planetary Radio Astronomy". Continuous ground-based observations and, in particular, space-borne measurements have meanwhile produced a comprehensive picture of a fascinating research area. Space missions as the Voyagers to the Giant Planets, specifically Voyager 2 further to Uranus and Neptune, Galileo orbiting Jupiter, and now Cassini in orbit around Saturn since July 2004, provide a huge amount of radio data, well embedded in other experiments monitoring space plasmas and magnetic fields. The present paper as a condensation of a presentation at the Kleinheubacher Tagung 2013 in honour of the 100th anniversary of Prof. Karl Rawer, provides an introduction into the generation mechanism of non-thermal planetary radio waves and highlights some new features of planetary radio emission detected in the recent past. As one of the most sophisticated spacecraft, Cassini, now in space for more than 16 years and still in excellent health, enabled for the first time a seasonal overview of the magnetospheric variations and their implications for the generation of radio emission. Presently most puzzling is the seasonally variable rotational modulation of Saturn kilometric radio emission (SKR) as seen by Cassini, compared with early Voyager observations. The cyclotron maser instability is the fundamental mechanism under which generation and sufficient amplification of non-thermal radio emission is most likely. Considering these physical processes, further theoretical investigations have been started to investigate the conditions and possibilities of non-thermal radio emission from exoplanets, from potential radio planets in extrasolar systems.

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The reversal of the rotational modulation rates of the north and south components of Saturn kilometric radiation near equinox

Cited by 67 publications

References 22 publications

A possible influence of the Great White Spot on Saturn kilometric radiation periodicity

A possible influence of the Great White Spot on Saturn kilometric radiation periodicity

The rotation of the plasmapause-like boundary at high latitudes in Saturn's magnetosphere and its relation to the eccentric rotation of the northern and southern auroral ovals

Planetary radio astronomy: Earth, giant planets, and beyond

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