Coupled SKR Emissions in Saturn’s Northern and Southern Ionospheres
Kivelson, Margaret G.; Jia, Xianzhe
2018-04-16
Citation
Kivelson, Margaret G.; Jia, Xianzhe (2018). "Coupled SKR Emissions in Saturn’s Northern and Southern Ionospheres." Geophysical Research Letters 45(7): 2893-2900.
Abstract
Kilometric radiation (SKR) emitted above Saturn’s auroral ionosphere is modulated in intensity at periods close to the planetary rotation period; SKR periods differ slightly for sources in the north and in the south. Although there is good evidence that the signals are generated independently in the two hemispheres, it is also well established that during southern summer power emitted from the northern hemisphere is modulated in intensity not only at the northern period but also at the southern period, an observation that requires an explanation. We examine the idea that the signal in the north at the southern period is a secondary effect of the strong field‐aligned current system centered at 270° that drives the southern signal. Basing our analysis on studies of field‐aligned current systems in the terrestrial and Jovian magnetospheres, we argue that the parallel electric fields that drive electrons into the southern auroral ionosphere and generate SKR are, at least in part, bidirectional and thus capable of accelerating electrons toward the opposite hemisphere where the secondary signal is detected with intensity lower than that of the locally generated signal. This interpretation implies that the atmospheric process that modulates the periodic responses can operate independently in each hemisphere.Plain Language SummaryRadio frequency signals with wavelengths of order 1 km emitted from high latitudes at Saturn vary in intensity at close to the planetary rotation period. Signals emitted from the southern and northern hemispheres are modulated at slightly different periods. It has been shown that these signals are generated in regions above the atmosphere where electrons accelerated to high velocities move toward the planet along the planetary magnetic field, generating intense electric current. Refined analysis has shown that sometimes the emissions are modulated not only at the dominant period for that hemisphere but also at the period of the opposite hemisphere. The mechanism for generating, for example, southern period emissions in the northern hemisphere has not been established. We propose that where electrons are accelerated in the southern hemisphere, they are accelerated both downward and upward along the planetary magnetic field. The upward moving electrons from the south move downward as they approach the northern hemisphere end of the magnetic field line, generating emissions with an intensity modulated at the southern period. This model implies that the peak emission at the southern period should occur at the same time north and south, a feature that has not yet been tested.Key PointsWe describe the generation of coupled north‐south SKR emissions observed at SaturnThe SKR emission in the north at the southern period is interpreted as a secondary effect of the strong field‐aligned current system that drives the southern signalThe signals at the southern period should appear at 270° southern PPO phase in both hemispheresPublisher
Cambridge University Press Wiley Periodicals, Inc.
ISSN
0094-8276 1944-8007
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