Local time distribution of low and middle latitude ground magnetic disturbances at sawtooth injections of 18–19 April 2002

Abstract

During a magnetic storm of 18 April 2002, quasi‐periodic variations of the low‐energy electron flux were observed by the LANL satellites at geosynchronous orbit; this phenomenon has been called the “sawtooth event.” During this event, on the ground, magnetic bays and Pi 2 pulsations took place corresponding to each enhancement of the particle flux, and they had features typical to usual substorms. However, unlike typical substorms, the ACE satellite observed no apparent northward turnings of the IMF corresponding to the sawtooth event. In this study, we used ground magnetic data from middle‐ and low‐latitude stations which are distributed widely in the longitudinal direction, selected from the CPMN (Circum‐Pan Pacific Magnetometer Network) and INTERMAGNET stations and compared the magnetic variations during the sawtooth event with that of the typical substorm (Lester et al., 1984). We found that the local time distribution of the polarization axis of the Pi 2 pulsations show a good agreement with that for a typical substorm, except that the local time width of the expected current wedge was 12 hours. On the other hand, the H component is predominant in the amplitude of the magnetic bay on the ground; the distribution of the H component also suggests a 12‐hour‐wide current wedge, which did not develop much in time. From these features, it is suggested that a current wedge was formed during this sawtooth event, and it generated the Pi 2 pulsations on the ground. However, the local time width of the current wedges is much wider than typical substorms, and its uniqueness causes the ground features different from typical substorm‐associated magnetic variations on the ground.