Properties of Plasmoids Observed in Saturn's Dayside and Nightside Magnetodisc

Plasmoid is a key structure for transferring magnetic flux and plasma in planetary magnetospheres. At Earth, plasmoids are key media which transfer energy and mass in the "Dungey Cycle." For giant planets, plasmoids are primarily generated by the dynamic processes associated with "Vasyliunas cycle." It is generally believed that planetary magnetotails are favorable for producing plasmoids. Nevertheless, recent studies reveal that magnetic field lines could be sufficiently stretched to allow magnetic reconnection in Saturn's dayside magnetodisc. In the study, we report direct observations of plasmoids in Saturn's dayside magnetodisc for the first time. Moreover, we perform a statistical investigation on the global plasmoid electron density distribution. The results show an inverse correlation between the nightside plasmoid electron density and local time, and the maximum plasmoid electron density around prenoon local time on the dayside. These results are consistent with the magnetospheric circulation picture associated with the "Vasyliunas cycle."