Coincident POLAR/UVI and WIND observations of pseudobreakups

Using POLAR/UVI global images, we have identified a period of successive mi nor auroral activations during which WIND was making a perigee pass (X simi lar to - 11 R-E) These auroral brightenings are interpreted to be pseudobre akups due to the lack of global expansion. Large magnetic field fluctuation s and high earthward ion velocity moments measured by the WIND spacecraft s how a nearly one-to-one correspondence with the auroral intensifications. A nalysis of the plasma parameters indicates that there is no difference in t he behavior of the plasma during pseudobreakups as compared to substorm exp ansive phase onset. Inspection of the ion distribution functions during hig h velocity moment events reveals the presence of a two component plasma. Th e particles contributing to the large mean velocities are energetic ions wi th energies from similar to 2 to 27 keV. We conclude that pseudobreakups ar e the ionospheric signature of high velocity moment events.