Characterizing the 18 April 2002 storm-time sawtooth events using ground magnetic data

Beginning during the last half of the main phase and extending for over 12 hours, the 18 April 2002 magnetic storm is dominated by sawtooth oscillations. We examine the ground magnetic signatures of these events at both high latitudes and low latitudes. The first immediate observation is that the magnetic signatures from one sawtooth to another can show considerable variation. Thus the current systems associated with these events show considerable variation in location, pattern, and strength from one oscillation to the next. The characteristics of the magnetic disturbance for each sawtooth has little to distinguish it from the typical substorm expansion magnetic disturbance field except that some of the sawteeth disturbance profiles are broader in local time than observed during typical substorms. The injection region determined from the energetic particle flux measurements at geostationary orbit is generally broad, extending across the entire tail and past the terminators into the dayside. The injection region is usually wider than the magnetic disturbance profile at the peak of the dipolarization. There appears to be no relationship between the magnetic disturbance profile and the location and strength of the injection boundary. Finally, sawtooth events appear to be driven by a steady solar wind driver and to develop during a period of already enhanced ring current.