Sawtooth Events During Steadily Depressed Dst

A series of sawtooth oscillations were observed during a magnetic cloud event on October 21-22, 2001. The storm main phase was driven by the cloud sheath region behind the interplanetary shock. The cloud proper had IMF Bz close to zero at its leading edge and negative at the trailing edge. The quasi-steady oscillations causing sawtooth-like behavior in the particle injections were observed during the negative IMF Bz period at the trailing edge of the cloud. The particle injections were recorded at multiple locations by the LANL spacecraft, and they were associted with strong dipolarizations of the nightside magnetic field, as recorded by the Polar spacecraft at 8 Re in the premidnight sector. During that time, ground-based observations showed quasi-continuous electrojet activity at a level exceeding 1000 nT in the AL index. The Dst index stayed at about -150 nT, showing no further enhancement even though the IMF Bz was negative, indicating that there was a rough balance of the energy input and dissipation processes. On the other hand, each of the sawtooth oscillations were seen as a positive deflection in the SYM-H index and a strong enhancement in the ASY-H index. These factors indicate that the sawtooth events were associated with field dipolarizations together with strongly asymmetric ring current formation. We discuss the global solar wind - magnetosphere - ionosphere coupling and the details of magnetospheric and ionospheric processes during the sawtooth events during this storm.