Earthward flow bursts, auroral streamers, and small expansions

Earthward flow bursts associated with small auroral expansions, including pseudobreakups, and auroral streamers are studied by using Geotail plasma and magnetic field data and Polar ultraviolet imager data. These flow bursts are accompanied by dipolarization and decrease in the plasma pressure, which are consistent with the characteristics of so-called bubbles, and have a timescale of 2.5 min on average. Based on a statistical study of the flow bursts, it is shown that the location of the flows are centered about 0.4 hour magnetic local time east of the center of auroral expansion and are localized with a width of 3 - 5 R-E. This relationship supports the idea that a dawn-to-dusk polarization electric field is created in the bubble to enhance the flows. The flow bursts associated with the small expansions, which are mainly observed in the region earthward of 15 R-E, shaw more distinct signatures of compression at the front side of the flow, which possibly leads to the stopping of these flows. Flow bursts related to auroral streamers, which are observed mainly tailward of 15 R-E, take place during relatively thick plasma sheet configurations, and are accompanied by stronger flow shear.