The ENA, Ring Current, and Auroral Response to "Sawtooth Injections"
in the October 4-6, 2000 Storm

Reeves, G. D., M. G. Henderson, R. M. Skoug, M. F. Thomsen,
J.-M. Jahn, C. J. Pollock, P. C. Brandt, D. G. Mitchell, and S. B. Mende,

The October 4-6 geomagnetic storm reveals several interesting
behaviors that illuminate the injection of plasmasheet material into
the inner magnetosphere and the subsequent ring current and auroral
responses. The storm began on October 4 in the second half of a
North-then-South magnetic cloud. For nearly all of October 4 the IMF
was only moderately southward with Bz around -10 nT. During that
period of modest solar wind energy input geosynchronous satellites
saw a series of "sawtooth injections" which have a very
characteristic temporal flux profile indicative of injection followed
immediately by renewed plasmasheet thinning. Each sawtooth injection
involves a large portion of the nightside and dusk-side
magnetosphere. The injections are each accompanied by brightening of
the auroral over a broad and expanded auroral oval. The
geosynchronous injections are also apparent in simultaneous ENA
images from the POLAR and IMAGE spacecraft which show that there is a
true injection of fresh plasmasheet material into the inner
magnetosphere and not simply an adiabatic reconfiguration of the
magnetic field. During the period of sawtooth injections the Dst
index decreased slowly to nearly -150 nT over an approximately
20-hour period. During that 20-hour decrease of Dst there is no
evidence of trapping of injected ring current particles and nearly
the entire build-up appears to be partial or untrapped ring current.
The magnetospheric dynamics share many of the features of a "steady
magnetospheric convection" event in spite of the fact that there was
nothing steady about the response in the inner magnetosphere. The
long and slow main phase also provides an unusual opportunity for
spacecraft to observe the dynamics during this event.