An Auroral Streamer Associated with Magnetic Reconnection in the Near-Earth Magnetotail Before Substorm Initial Brightening

While a lot of equatorward moving auroral streamers that emerged at the auroral poleward boundary in relation to distant magnetotail reconnection have been reported previously, those that emerged between the auroral poleward and equatorward boundaries in relation to near-Earth reconnection have scarcely been reported. THEMIS ground-based all-sky imagers, however, observed that a bright equatorward moving auroral streamer emerged between the auroral poleward boundary and the equatorward substorm onset arc and arrived at the onset arc before initial brightening. Simultaneously a THEMIS spacecraft observed a tailward moving traveling compression region and plasmoid in the near-Earth magnetotail, indicating that magnetic reconnection occurred earthward of this spacecraft. We suggest that this auroral streamer possibly corresponds to the counterpart earthward flow generated by near-Earth reconnection and is auroral evidence for near-Earth reconnection as substorm trigger.