Magnetospheric Sawtooth Events During Solar Cycle 23

We report on the relationship between occurrence of magnetospheric sawtooth oscillation events and solar activity from January 1995 to December 2007, which nearly covers the full solar cycle 23. There are 133 sawtooth events in total. We find no clear trend between the number of sawtooth events and solar activity. The number of sawtooth events reaches its maximum in the initial descending phase in 2001 and 2002. However the numbers of sawtooth events drop during both the solar minimum (around 1996 and 2007) and solar maximum (around 2000). This hints that the solar wind structures during the descending phase, which are mostly stream interactions, are effective at producing sawtooth events. While interplanetary coronal mass ejections around solar maximum produce a large number of storms and even super storms, they are less effective to produce sawtooth events. We propose that sawtooth events tend not to occur during very intense solar wind drivers as the magnetosphere becomes a chaotic system and it is unlikely that it can load and unload energy in regular oscillation cycles characteristic of global sawtooth oscillations.