资源环境科技发展态势分析平台

The inner boundary of Saturn's electron radiation belts, near the planet's A ring (similar to 2.27 R-s), 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. Prenoon, the boundary oscillates toward and away from the A ring with a 2-week period. Postnoon, it maps persistently near the F ring (similar to 2.32 R-s) 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.