Large Magnetic Flux Ropes Outside Saturn’s Magnetodisc: 7 yr of Cassini Observations

Abstract Large magnetic flux ropes mediate plasma transport, particle acceleration, and energy dissipation in planetary magnetospheres. While well studied in the solar wind-driven terrestrial magnetosphere, their evolution at Saturn, where strong internal driving combines with intermittent solar-wind forcing under variable upstream conditions, remains less well characterized. We present a systematic survey of 7 yr of Cassini magnetometer and plasma data, focusing on the low-latitude region outside Saturn’s magnetodisc where the magnetopause and magnetosheath respond directly to the solar wind. Using stringent selection criteria, we identify 67 large-scale flux rope candidates. Minimum variance analysis constrains axial orientations for all events, and for nine events with high-quality plasma measurements, we apply three-dimensional Grad–Shafranov reconstructions to resolve magnetic structure and flux content. The resulting ropes span diameters of 0.7−13.2 Saturn radii and magnetic fluxes of 6 × 10 6 to 8.7 × 10 8 Wb, generally exceeding the size range of previously reported flux transfer events at Saturn. We find a pronounced dawn–dusk asymmetry: flux ropes occur more often near dawn but are typically larger near dusk, consistent with Kelvin–Helmholtz instability (KHI) formation. A substantial subset shows north–south axes, also consistent with KHI. Individual events can transport up to ∼10% of the open magnetic flux exchanged during a Dungey cycle, indicating that these flux ropes can move substantial magnetic flux across Saturn’s magnetopause and contribute meaningfully to magnetospheric circulation.