Abstract
AbstractThe L shell distributions of MeV electrons in Saturn's radiation belt are investigated orbit by orbit for the 13‐year exploration of Cassini. It is found that in addition to the monotonic decrease profiles, there are orbits showing superimposed transient extensions. The extensions are found to stand out above the background population during 50% of belt crossings. We estimate that there is high probability (>72%) that transient extensions contribute more than 10% electron content in the radiation belt. The high occurrence frequency of one extension every 2–3 weeks, together with the relative content, demonstrate that the extensions constitute a regular and fundamental process populating and sustaining the electron belts of Saturn. The transients regularity excludes interplanetary coronal mass ejections as dominant trigger and implies corotation interaction regions and/or internal processes as candidates. Statistical results suggest that the communication of electrons between the middle magnetosphere and the radiation belts is largely through convective radial transport, which produces transient radiation belt extensions.
Highlights
Together with the observations at the middle and outer magnetosphere, the transient extension was attributed to a tail acceleration event that evolved to the inner belts through the ring current
There are two components contributing to the nonmagnetospheric signals: the gamma rays and neutrons produced by radioisotope generators (RTG) of Cassini, and Galactic Cosmic Rays (GCR)
Roussos et al (2018) show how a very strong shock associated to an Interplanetary Coronal Mass Ejection (ICME) event was behind the appearance of an electron belt transient seen on day 97/2012
Summary
The occurrence frequency of Saturn radiation belt transient extensions indicates a possible role for Corotating Integration Regions (CIRs). That transient extensions contribute >10% electron content in the radiation belt. Preference in outside-in cases independent of local time suggests that electron belts may be largely sustained by convective inflow of transient. Sustaining Saturn's electron radiation belts through episodic, global-scale relativistic electron flux enhancements. Journal of Geophysical Research: Space Physics, 125, e2019JA027621. Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China, 4 Max Planck Institute for Solar System Research, Göttingen, Germany
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