The motion and deceleration process of plasma sheet high speed flows have great significance to magnetospheric particle acceleration, magnetic field perturbation, triggering of substorm and formation of the substorm current wedge. During February to April 2009 THEMIS_A and THEMIS_ E are separated only along Z direction. Such special configuration allows joint observations of high-speed flows at both the center and boundary of the plasma sheet. Based on case study and statistical analysis, we found that for 89% of the earthward high-speed flows, the probe far from the neutral sheet observed the high-speed flow first and the flow is mainly field-aligned. Our results also show that the X-component of the high-speed flow in the plasma sheet boundary is greater than that in central plasma sheet. With the hypothesis that parallel flow remains the same speed during its propagation and central plasma sheet stream uniformly brakes, we deduced the location where the stream deceleration begins to be between 15Re and 20Re down-tail. This is consistent with near-earth reconnection site which have been proposed before in literature. In addition, the statistics showed that high speed flows in the central plasma sheet are accompanied by stronger dipolarization fronts than those in the plasma sheet boundary。
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