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Global sawtooth oscillations are periodic changes in the morphology of the magnetosphere wherein the magnetic field in the inner regions strongly stretches and then rapidly crashes or dipolarizes. The period of the oscillation is about three hours, with the crash phase lasting 5–15 min. At geosynchronous orbit, a sawtooth oscillation of the magnetosphere appears as a periodic decline and rapid recovery of the energetic particle fluxes at all local times; such an oscillation is shown in Figure 1.

Global sawtooth oscillations occur during some, but not all, geomagnetic storms. Owing to the extremely large amplitudes of the sawtooth oscillations, nearly all measurements taken in the magnetosphere show signatures of the sawtooth oscillations.