IGPP Seminar Series

Magnetospheric Sawtooth Events and Observational Evidence for an Inside-Out Substorm Onset Scenario

by Mike Henderson
Space Science and Applications, Los Alamos National Laboratory


Sawtooth events are 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 show that the majority of teeth comprising a sawtooth event are in fact substorms. In addition, we find that the geosynchronous particle injections were neither globally simultaneous nor globally dispersion-less, but were instead consistent with a night-side/dusk-side 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, mid and low latitude positive H-bays, a partial recovery in Sym-H, and the onset of Pi2 ULF pulsations. We also 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. Analysis of a sawtooth-like substorm event is also presented which provides support for a substorm onset scenario in which a localized inner magnetospheric instability developed first and was later followed by the development of a Near Earth Neutral Line (NENL) farther down-tail.
Tuesday, 07 April 2009
3853 Slichter Hall
Refreshments at 3:45 PM
Lecture at 4:00 PM