Earth's Magnetosphere Response to the 12 May, 2001 Interplanetary Coronal Mass Ejection

A sawtooth event is clearly identified from the low energetic proton flux measurements at geosynchronous orbit on 12 May, 2001. The Earth's magnetosphere is in steady magnetospheric convection (SMC) mode right before the sawtooth event based on spacecraft aurora observations. By examination of the solar wind driver, we find these two events are related to an interplanetary coronal mass ejection (ICME). The Earth's magnetosphere enters the SMC mode when southward interplanetary magnetic field is roughly steady at ~ 6 nT before the arrival of the ICME. The sawtooth oscillation occurs during the sheath region of the ICME when solar wind pressure is enhanced and the IMF is highly variable. We investigate the magnetosphere change between the two modes in response to the changing interplanetary conditions. The relationship between the onsets of individual teeth and solar wind changes are examined in detail.