Earthward flow bursts, auroral streamers, and small expansions

Earthward flow bursts associated with small auroral expansions, including p seudobreakups, and auroral streamers are studied by using Geotail plasma an d magnetic field data and Polar ultraviolet imager data. These flow bursts are accompanied by dipolarization and decrease in the plasma pressure, whic h 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 b ursts, it is shown that the location of the flows are centered about 0.4 ho ur magnetic local time east of the center of auroral expansion and are loca lized 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 enhan ce the flows. The flow bursts associated with the small expansions, which a re mainly observed in the region earthward of 15 R-E, shaw more distinct si gnatures 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 she ar.