Henderson, M. G. and Skoug, R. and Donovan, E. and Thomsen, M. F. and Reeves, G. D. and Denton, Michael H. and Singer, H. J. and McPherron, R. L. and Mende, S. B. and Immel, T. J. and Sigwarth, J. B. and Frank, L. A. (2006) Substorms during the August 10-11 sawtooth event. Journal of Geophysical Research, 111 (A06206). pp. 1-32. ISSN 0148-0227
Abstract
Sawtooth events have been identified at geosynchronous orbit as large-amplitude quasiperiodic (2–4 hour period) modulations of the energetic electron and ion fluxes. They are called sawtooth events because the shape of the flux versus time profiles are composed of rapid increases followed by gradual decreases that resemble the teeth on a saw blade. Although much of the phenomenology associated with sawtooth events is substorm-like, there is still debate as to whether the individual teeth are substorms or not. Here we examine each of the teeth associated with the 10–11 August 2000 sawtooth event in detail. We find that all but one of the teeth were associated with injections at geosynchronous orbit and that most of the teeth were consistent with the hypothesis that they are predominantly caused by unusually large and longitudinally extended substorms. A few were unclear or complex, and the final flux enhancement at 1845:36 UT was not a substorm but a solar wind shock-associated disturbance. In addition, the presence of numerous dispersionless flux perturbations in the LANL SOPA data provides support for the hypothesis that solar wind pressure variations can modulate the flux profiles to some extent. For the substorm events we find that the geosynchronous particle injections were neither globally simultaneous nor globally dispersionless but were instead consistent with a nightside/duskside source in most cases. Similarly, we show that the field dipolarizations were also not global and simultaneous. Each of the substorms was also associated with high-latitude negative H bays, middle- and low-latitude positive H bays, a partial recovery in Sym-H, and the onset of Pi2 ULF pulsations. In addition, we show that the auroral distribution develops in a systematic way during each cycle of a sawtooth substorm event. Specifically, a localized auroral onset develops on the lower branch of a thinned double-oval distribution. The location of onset is typically premidnight and often occurs to the west of intense omega band forms. This is followed by westward, eastward, and poleward expansion and the copious production of auroral streamers which can develop in complex patterns including a “spoke-like” morphology. The double-oval configuration thins again during the stretching phase until the next onset occurs and the cycle repeats. A schematic representation of the auroral dynamics associated with sawtooth substorms is also presented.