ULYSSES OBSERVATIONS OF COROTATION LAGS IN THE DAYSIDE JOVIAN MAGNETOSPHERE - AN EVALUATION OF THE HINGED MAGNETODISC AND MAGNETIC ANOMALY MODELS

Ulysses observations during the inbound leg of the February 1992 encou nter with Jupiter offer the opportunity to evaluate both the hinged ma gnetodisc and the magnetic anomaly models currently used to describe t he Jovian magnetospheric corotation lag. Particle and field detectors on board Ulysses measure signatures of the current and plasma sheets. The locations of these sheets in radius and system III longitude are t hen used as inputs to the models. It is shown that the hinged magnetod isc model is able to explain some characteristics of the data but unab le to explain others. The magnetic anomaly model appears to account fo r the overall nature of the magnetospheric corotational lag; however, it, too, cannot fully account for the Ulysses data. A modification of the magnetic anomaly model is offered which adequately explains the Ul ysses data and, with the assumption of a sufficiently significant, tim e-dependent Iogenic plasma source, explains data from previous Jupiter encounters as well.