TITLE:  Magnetosphere-ionosphere coupling during sawtooth events

ABSTRACT:
Sawtooth events are quasiperiodic injections of energetic particles which are observed at geosynchronous orbit. They differ from ordinary substorm injections in that sawtooth injections are observed over a wider range of local times, including the dayside, whereas ordinary substorm injections are confined to near midnight. The physical mechanism for driving sawtooth events has been a matter of debate for many years, with some modelers predicting that at least some sawtooth events are driven by a feedback of nightside ionospheric outflow on the reconnection region in the tail. In a study of in situ data from FAST in the ionosphere and Cluster in the tail, along with IMAGE FUV remote views of the auroral oval, we show that there is no evidence of ionospheric ion feedback in sawtooth events, both in two case studies and in a survey of all known sawtooth events from 2001-2007 for which Cluster data in the plasma sheet are available. We also examine discrepancies in timing between sawtooth injections and optical substorm onsets, noting that there are cases where sawtooth injections are not associated with any auroral response. This result suggests that our understanding of the phenomenology of both sawtooth injections and substorms is incomplete.