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We investigated the temporal and spatial development of the near-Earth\udmagnetotail during substorms based on multi-dimensional superposed-epoch\udanalysis of Geotail data. The start time of the auroral break-up (t=0) of\udeach substorm was determined from auroral data obtained by the Polar and\udIMAGE spacecraft. The key parameters derived from the plasma,\udmagnetic-field, and electric-field data from Geotail were sorted by their\udmeridional X(GSM)–Z(proxy) coordinates.\ud\ud \ud\udThe results show that the Poynting flux toward the plasma-sheet center\udstarts at least 10 min before the substorm onset, and is further enhanced at\udX~−12 RE (Earth radii) around 4 min before the onset. Simultaneously,\udlarge-amplitude fluctuations occurred, and earthward flows in the central\udplasma sheet between X~−11 RE and X~−19 RE and a duskward flow\udaround X=−10 RE were enhanced. The total pressure starts to decrease around\udX=−16 RE about 4 min before the onset of the substorm. After the substorm\udonset, a notable dipolarization is observed and tailward flows commence,\udcharacterised by southward magnetic fields in the form of a plasmoid.\ud\ud \ud\udWe confirm various observable-parameter variations based on or predicted by\udthe relevant substorm models; however, none of these can explain our results\udperfectly. Therefore, we propose a catapult (slingshot) current-sheet\udrelaxation model, in which an earthward convective flow produced by catapult\udcurrent-sheet relaxation and a converted duskward flow near the Earth are\udenhanced through flow braking around 4 min before the substorm onset. These\udflows induce a ballooning instability or other instabilities, causing the\udobserved current disruption. The formation of the magnetic neutral line is a\udnatural consequence of the present model, because the relaxation of a highly\udstretched catapult current-sheet produces a very thin current at its\udtailward edge being surrounded by intense earthward and tailward magnetic\udfields which were formerly the off-equatorial lobe magnetic fields. This\udlocation is the boundary between a highly stressed catapult current sheet\udand a Harris-type current sheet characterized by little stress. In addition,\udthe flows induced around the boundary toward the current-sheet center may\udenhance the formation of the magnetic neutral line and the efficiency of\udmagnetic reconnection. After magnetic reconnection is induced, it plays a\udsignificant role in driving the substorm

Statistical visualization of the Earth's magnetotail based on Geotail data and the implied substorm model