Sources, sinks and transport of energetic electrons near Saturn's main rings

The inner boundary of Saturn's electron radiation belts, near the planet's A‐ring (∼2.27 Rs), is studied using Cassini's Proximal orbit measurements. We find that variable convective flows transport energetic electrons to the A‐ring, which absorbs them instantaneously, forming the inner belt boundary. These flows are also responsible for a variable and longitudinally asymmetric boundary configuration. Pre‐noon, the boundary oscillates towards and away from the A‐ring with a two‐week period. Post‐noon, it maps persistently near the F‐ring (∼2.32 Rs) and coexists with localized MeV electron intensity enhancements (microbelts). We propose that the microbelts contain electrons in drift resonance with corotation, trapped in local‐time confined trajectories which result from the aforementioned convective flows. The microbelts' collocation with the F‐ring implies either a local, secondary electron production due to Galactic Cosmic Ray collisions with F‐ring dust, or an enhanced resonant electron trapping due to an electrodynamic interaction between the F‐ring and Saturn's magnetosphere.