Constraining the Length of the Reconnection Site in the Magnetotail using THEMIS Observations of Flux Ropes and BBFs

Magnetic field and plasma data from the outer pair of THEMIS spacecraft during the first tail seasons are used to identify bursty bulk flows (BBFs), flux ropes and travelling compression regions as they encounter both spacecraft. BBFs were preferentially observed if THEMIS B and C were located within 1 R_E of each other in the dawn-dusk direction, suggesting that the flow channel (and therefore the reconnection site) is extremely narrow. This is supported by observations of flux ropes (FRs) in the plasma sheet, and travelling compression regions (TCRs) in the lobes. FR/TCR signatures that are observed by both THEMIS B and C are extremely rare, despite the relaxation of the requirement that the spacecraft be located in the plasma sheet in order to observe the signatures. Three case studies are presented where the outer spacecraft observed an Earthward-moving TCR, and the inner spacecraft subsequently observed an Earthward-moving flux rope. In all cases the spacecraft were aligned (to within 1 R_E) in the dawn-dusk direction. Flux rope orientation at both spacecraft is determined using minimum variance analysis, and the velocity is determined using inter-spacecraft timing analysis and in situ plasma observations.