The structure of the fast plasma flow in the plasma sheet: Comparison between observations and two-fluid simulations

The fast plasma flow in the plasma sheet is one of the most important features of tail dynamics. The present study examines how magnetic field and plasma parameters change in association with the fast plasma flow. A superposed epoch analysis is conducted for 818 earthward flow events and 290 tailward flow events observed by the Geotail satellite in the near-Earth (X > -31 RE) region. The results are summarized as follows: (1) The average magnetic field becomes more dipolar in the course of the fast earthward flow; (2) Sharp dipolarization tends to be preceded by the initiation of fast flows, a transient decrease in Bz, and a transient increase in the plasma density; (3) The corresponding signatures can also be found for the tailward flow, although they are less clear; (4) Whereas the average plasma density decreases in association with the fast flow irrespective of the flow direction, the average ion temperature increases for the earthward flow and decreases for the tailward flow; (5) The average plasma and total pressures decrease in the course of the fast flow, suggesting the reduction of the lobe field strength. These results are compared with the fast plasma flow modeled by a two-fluid simulation with a focus on (2). The results of the simulation reveal that the initial fragmenting of the current sheet into multiple neutral lines develops into a larger-scale structure as one neutral line dominates others, and the signatures of these dominated neutral lines are convected along with the fast reconnection outflow. The present study will address similarities and difference between the associated internal structure of the simulated fast flow and the result of the superposed epoch analysis.