An Investigation of Flow Shear and Diamagnetic Drift Effects on Magnetic Reconnection at Saturn's Dawnside Magnetopause

At Saturn, solar wind driving of the magnetosphere is predicted to be reduced due to the extreme rotationally driven interior. As a result, the rotationally driven plasma corotates with the planet, possibly out to the magnetopause. Modeling suggests that this corotation should set up conditions that are unfavorable for the onset of magnetic reconnection on the dawnside magnetopause due to the generation of a significant flow shear. The flow shear model being tested makes use of idealized steady state models and a dominant east-west interplanetary magnetic field orientation with a slight northward component. When the flow shear is larger than the Alfven speed, the model indicates that reconnection is suppressed. In this study, we employ observations from Cassini, when the interplanetary magnetic field has a northward component, to test this flow shear suppression model and whether reconnection is suppressed by diamagnetic drifts. Observations from the electron spectrometer on the Cassini Plasma Spectrometer suite of instruments show that reconnection does occur at the dayside magnetopause of Saturn, even in locations where modeling suggests that conditions are unfavorable for its onset. The inconsistency between modeling and observations may be caused by the conditions and assumptions within the model itself. Furthermore, the occurrence of reconnection on the dawnside magnetopause in general may hint at additional complexities in the global structure of Saturn's magnetosphere.