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Abstract:
Banded structures observed in energetic particle spectrograms in the Earth's inner radiation belt and slot region, that is, “zebra stripes,” have been resolved in the Saturnian magnetosphere with Cassini. This study implements a large-scale statistical analysis of Saturnian zebra stripe properties in association with the noon-to-midnight electric field of the inner magnetosphere to which the stripes' origin was recently established. Cassini has detected zebra stripes extending between L-shells (L) of 5–9 for more than half of the orbits that crossed inward of L = 9. The amplitude of the stripes is 15 - 20% on average above the background differential energy flux, and their age is estimated to be 20–60 hr. The regular observation of zebra stripes suggests that their regeneration and the corresponding electric field enhancements develop over timescales comparable to their estimated lifetime (days), revealing that internal processes contribute to the electric field dynamics, in addition to a solar wind-induced variability indicated by previous investigations. The flux-enhanced stripes are traced back to the dayside, preferentially from postnoon, indicating an electric field orientation from postnoon to postmidnight. Our results further suggest that the electric field's offset from the noon-midnight line is subject to both L-shell and temporal dependencies, confirming the previous inferred variability.
