Magnetospheric currents during sawtooth events: Event-oriented magnetic field model analysis

The behavior of inner magnetosphere current systems associated with a sawtooth sequence is examined using empirical magnetic field models during a sawtooth event on 18 April 2002. Three different empirical magnetic field models were developed for the same time period. In each case, the models were fitted using in situ magnetic field observations to minimize the differences between the model and observed field values. The results were compared with those previously obtained for a sawtooth event on 22 October 2001. The main features, namely, strong stretching of both nightside and dusk sector magnetic field prior to the injection, strong currents near geosynchronous distance, and strong dusk-sector magnetic field stretching, were all reproduced by all three models also for the April 2002 event. We conclude that these are repeatable and characteristic features of sawtooth events and discuss how the model details influence the minor differences between the models. Simple drift trajectory calculations are used to show that the models, which reproduce the magnetic field quite well, also accurately represent the energetic proton drift periods at geosynchronous orbit.