Storm-time Sawtooth Flux Variations

R. M. Skoug, M. F. Thomsen, G. D. Reeves, J. E. Borovsky, M. G.
Henderson, H. O. Funsten, C. J. Pollock, J.-M. Jahn, D. J. McComas,
P. C. Brandt, D. G. Mitchell, H. J. Singer, S. B. Mende


During geomagnetic storms the fluxes of energetic particles observed
at geosynchronous orbit often exhibit a "sawtooth" profile, with
quasi-periodic repetitions of sudden flux increases followed by
gradual but dramatic decreases in flux.  Some studies have suggested
that each sawtooth is caused by a substorm injection, while others
have suggested that they instead represent some sort of global
oscillation of the magnetosphere.  In this study, we examine the
nature of sawtooth flux variations observed from July 2000 to
December 2001 using a combination of in situ observations from
geosynchronous satellites and global energetic neutral atom (ENA) and
UV images from the IMAGE spacecraft.  We find that sawtooth events
appear to be substorms on a more global scale.  These events show the
auroral signatures of substorms, increases in the global particle
flux, and increases in the sym-H index (sym-H becomes less negative)
at the flux increases.  Each sawtooth enhancement is first observed
near midnight, and the events then propagate rapidly around the Earth
at speeds exceeding the particle drift speeds.  Sawtooth enhancements
tend to occur during times of moderate solar wind driving.  The
geomagnetic field stretches during the decay phase of each sawtooth,
and dipolarizes at each flux increase.  The dipolarizations are often
very large (20-50 degrees), and are observed at nearly all local
times, again showing the global nature of these events.  In addition,
variations in the azimuthal angle of the geomagnetic field are also
observed at sawtooth enhancements.  We examine the implications of
these magnetic field variations for the current systems responsible
for sawtooth enhancements.

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To be presented at the 2002 Spring A.G.U. Meeting, 
Washington, D.C., U.S.A., 28-31 May 2002