Magnetospheric current systems during stormtime sawtooth events

The sawtooth event period embedded in a storm interval on 2001-10-22 is analyzed using magnetic field modeling techniques. The model current systems show that sawtooth injections are associated with strong stretching of both the nightside and dusk-sector magnetic field prior to the injection and a partial disruption of that current at the time of the injection. The currents are strongest near geosynchronous distance and in the premidnight sector. The strong dusk-sector field stretching produces very fast proton drift speeds, which can explain the near-simultaneous occurrence of the injections over a wide local time sector. Comparison of sawtooth periods with nonstorm substorms indicates that the tail field behavior resembles that of nonstorm substorms, but that the consequences of the stretching/dipolarization cycle are different from nonstorm times. As the drifting protons during sawtooth events are mostly on open drift paths, the symmetric ring current is only slightly affected, while large variations are seen in the asymmetric ring current. The three-spacecraft magnetic field measurements together with the Dst index were sufficient to constrain the magnetic field model to give a reasonably accurate global magnetic field representation, as confirmed by an independent test using measurements not used in the fitting. Thus we conclude that the empirical modeling methods can be quite reliable in predicting the large-scale fields when suitable observations are available.