Substorms during the 10-11 August 2000 sawtooth event

M.G. Henderson, R. Skoug, E. Donovan, M.F. Thomsen, G.D. Reeves, M.H. Denton, 
H.J. Singer, R.L. McPherron, S.B. Mende, T.J. Immel, J.B. Sigwarth, 
and L.A. Frank


Sawtooth events have been identified at geosynchronous orbit as large-amplitude
quasiperiodic (2Ð4 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 10Ð11 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.

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Journal of Geophysical Research, 111, A06206, doi:10.1029/2005JA011366, 2006