Investigation of the period of sawtooth events

A sawtooth event is identified as a series of energetic particle flux variations, i.e., rapid increases following slow decreases, from geosynchronous satellites observations. The saw blade shape is prominent in the proton flux with energy range between 50 and 400 keV. Though sawtooth events are described as large‐amplitude oscillations with periods between 2 and 4 h on the basis of case studies, their period has not been accurately determined by previous studies. In this study, we have identified 111 sawtooth event intervals, which include 438 individual teeth, from January 1998 to December 2007. We find the average period is 179.6 min. However, the period shows large variations from event to event, even from tooth to tooth in the same sawtooth interval. The variability is independent with the length of the period and the number of oscillations, so we conclude that sawtooth events are quasi‐periodic events instead of periodic events.