R. M. Winglee, R. M. Skoug, A. T. Y. Lui, R. P. Lin, R. P. Lepping, S. Kokubun, G. Rostoker, and J. C. Samson

Geophysics Program, University of Washington, Seattle

The dynamics of an isolated substorm observed on Feb. 9, 1996 using is examined using (1) in situ observations from Wind, Geotail and IMP 8 , (2) ground-based observations from Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS) and (3) global simulations. The CANOPUS data show that the substorm has the classical signatures of the expansion of the auroral oval during the growth phase, and the intensification and poleward motion of the high latitude portion of the auroral oval. The enhanced convection of dayside magnetic field into the nightside that drives the growth phase also produces the growth of the lobes in the north-south direction, forcing the high-latitude magnetopause and bow shock to move outwards. This motion causes the bow shock crossing of IMP 8 at the beginning of the growth phase. The tail dynamics as observed by Geotail are very much more complicated. Small (-1 nT) B_Z values are observed in the tail during the growth phase, when Geotail at about 35 R_E down the tail makes several crossings of the current sheet. These results as well as the global simulations suggest that for this substorm a near-Earth neutral point can form during the growth phase but not trigger substorm onset. Additional processes appear to be necessary to either locally disrupt the current sheet earthward of Geotail or to move the existing neutral point earthward in order to produce the large (-5 nT) negative B_Z values observed at substorm onset.

Geospace Mass and Energy Flow, ed. By J. L. Horwitz, S. L. Gallagher, and W. K. Peterson, Geophys. Monograph 104, pg. 181, 1998