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Bader et al on-line (10 Feb 2019).pdf (3.24 MB)

Modulations of Saturn's UV Auroral Oval Location by Planetary Period Oscillations

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journal contribution
posted on 2019-05-15, 09:12 authored by A Bader, SV Badman, J Kinrade, SWH Cowley, G Provan, W Pryor
It is well known that Saturn's magnetospheric dynamics are greatly influenced by the so-called planetary period oscillations (PPOs). Based on Cassini Ultraviolet Imaging Spectrograph (UVIS) imagery, it has been shown previously that the UV auroral intensity is clearly modulated in phase with rotating field-aligned current (FAC) systems associated with the PPOs. Here we expand upon this investigation by using the same data set to examine the PPO-induced spatial modulation of the main auroral oval. We present a robust algorithm used for determining the location of the main emission in Cassini-UVIS images. The location markers obtained are then used to calculate the statistical location of the auroral oval and its periodic displacement due to the PPO FACs and the related ionospheric flows. We find that the largest equatorward displacement of the main arc lags behind the PPO-dependent statistical brightening of the UV aurora by roughly 45–90° in both hemispheres and is not colocated with it as the present model based on magnetometer observations suggests. We furthermore find the center of the auroral oval by fitting circles to the main emission and analyze its elliptic motion as the entire oval is displaced in phase with the PPO phases. It is demonstrated that the periodic displacements of both the auroral oval arc and its center are larger when the two PPO systems rotate in relative antiphase than when they are in phase, clearly indicating that interhemispheric PPO FAC closure modulates not only the intensity but also the location of the main UV auroral emission.


A. B. was funded by a Lancaster University FST studentship. J. K. and S. V. B. were supported by STFC grant ST/M001059/1. S. V. B. was also supported by an STFC Ernest Rutherford Fellowship ST/M005534/1. Work at the University of Leicester was supported by STFC Consolidated Grant ST/N000692/1.



Journal of Geophysical Research: Space Physics, 2019, 124(2), pp. 952-970

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/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


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Journal of Geophysical Research: Space Physics


American Geophysical Union (AGU), Wiley





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UVIS data are available from the NASA Planetary Data System ( All PPO phase data (2004–2017) are available in the University of Leicester Research Archive (



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