Current wedge dynamics and associated transient electron precipitation during oscillatory flow braking

We study the ionospheric response to oscillatory braking of bursty bulk flow observed by THEMIS on 17 March 2008 just after 10:22 UT. By calculating different current components generated in the plasma sheet and correlating the space and ground observations we discriminate the ionospheric current relevant to the large-scale substorm wedge currents produced by the general reconfiguration of the magnetotail pressure gradient from the currents that appeared as a result of the flow oscillation. While the former currents are large and quasi-stable, the latter (oscillating) currents are substantially (2-3 times) weaker and flow in opposite directions during earthward and tailward flow bursts. The oscillating currents included the polarization current and the current generated by the oscillating part of the pressure gradient. The two oscillating currents appear to produce modulation of the ionospheric currents (with about 2.5 min period) that was seen as Pi2 pulsations in the ground magnetometer observations. Our estimates of the ionospheric conductance suggest that the damping of the plasma sheet flow oscillation is provided to a large extent by heating the ionosphere through Pedersen currents. Also, during the first two periods of the oscillatory flow braking the all-sky imager at Fort Yukon observed four auroral arcs: two during the earthward plasma sheet flows and the other two during the tailward flow rebounds. The auroral arcs appear to follow the location of the modulated upward field-aligned current. Based on THEMIS burst-mode electron and electromagnetic field wave data we discuss the mechanism of the electron precipitation into the loss cone that generated the auroral arcs.