Magnetic flux circulation in the rotationally driven giant magnetospheres

The giant‐planet magnetodiscs are shaped by the radial transport of plasma originating in the inner magnetosphere. Magnetic flux transport is a key aspect of the stretched magnetic field configuration of the magnetodisc. While net mass transport is outward (ultimately lost to the solar wind), magnetic flux conservation requires a balanced two‐way transport process. Magnetic reconnection is a critical aspect of the balanced flux transport. We present a comprehensive analysis of current sheet crossings in Saturn's magnetosphere using Cassini magnetometer data from 2004 to 2012 in an attempt to quantify the circulation of magnetic flux, emphasizing local time dependence. A key property of flux transport is the azimuthal bend forward or bend back of the magnetic field. The bend back configuration is an expected property of the magnetodisc with net mass outflow, but the bend forward configuration can be achieved with the rapid inward motion of mostly empty flux tubes following reconnection. We find a strong local time dependence for the bend forward cases, localized mostly in the postnoon sector, indicating that much of the flux‐conserving reconnection occurs in the subsolar and dusk sector. We suggest that the reconnection occur in a complex and patchy network of reconnection sites, supporting the idea that plasma can be lost on small scales through a “drizzle”‐like process. Auroral implications for the observed flux circulation will also be presented. Key Points Giant‐planet magnetodiscs are shaped by radial plasma transport Magnetic flux is transported radially outward with the plasma Magnetic reconnection circulates flux to the inner magnetosphere on the dayside