Physics
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsm14a..05h&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #SM14A-05
Physics
2704 Auroral Phenomena (2407), 2720 Energetic Particles: Trapped, 2788 Magnetic Storms And Substorms (7954), 2790 Substorms
Scientific paper
Sawtooth events have been identified at geosynchronous orbit as large amplitude quasi-periodic (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 comprised 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 August 10-11, 2000 sawtooth event in detail. We find that most of the flux enhancements were unambiguously substorms. A few were unclear or complex, and the final flux enhancement was not a substorm but a solar wind shock-associated disturbance. 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 source. 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, mid 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 pre-midnight 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.
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