Storm-Time Sawtooth Variations in the Magnetosphere
 
M. F. Thomsen, R. M. Skoug, 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, and R. Clauer
 

A powerful combination of global energetic neutral atom (ENA) imaging, 
in-situ plasma, energetic-particle, and magnetic-field measurements, and 
multi-station ground-based magnetometer measurements is brought to bear on 
the problem of the "sawtooth" ion flux modulations often observed at 
geosynchronous orbit during moderate storm-time conditions.  From a set of 
such events that have occurred since the launch of the IMAGE satellite, we 
find that sawtooth events have the appearance of geomagnetic substorms, but 
on a larger-than-usual scale.  Each sawtooth enhancement in the ion flux is 
observed first near midnight, with subsequent primarily-westward propagation 
and a corresponding auroral enhancement and SYM-H increase.  The geomagnetic 
field stretches in the declining phase of each flux enhancement, with a 
clear and often quite dramatic dipolarization with each sawtooth increase, 
especially in the afternoon and pre-midnight sectors.  Ground magnetometers 
show a corresponding weakening and strengthening of the mid-latitude field 
during the stretching and dipolarization phases, respectively.  This ground 
signature is present at all local times except in the midnight-to-dawn 
sector.  These sawtooth events appear to be a characteristic mode of 
magnetospheric response to moderately strong solar-wind driving. 
 
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To be presented at the AGU Western Pacific Geophysics Meeting, 
Wellington, NZ, July 9-12, 2002