Three-dimensional structure of magnetic reconnection in the magnetotail from Geotail observations

Three-dimensional structure of magnetic reconnection in the near-Earth magnetotail is explored using Geotail observations from 1996 to 2012. Magnetic reconnection is identified as a simultaneous plasma flow and magnetic field reversal near the neutral sheet with intense out-of-plane electron currents. There are 30 events in the region of -32 < X < -18 R_E (in the aberrated GSM coordinates) in the magnetotail. The dawn-dusk width (in the y direction) of the magnetic reconnection site is probably less than 8 R_E with its center in the premidnight region. The magnetic field structure in the x-z plane does not change significantly in the full width of the magnetic reconnection site. The ion inflow-outflow structure shows a marked edge effect in the duskside. As inflow, ions move toward the equatorial plane with an additional dawnward motion. This dawnward motion is more evident in the duskside. As outflows, ions escape tailward and earthward with a duskward motion, as expected from the Speiser motion, except at the duskside edge. At the duskside edge, almost all ions move dawnward, and only part of high-energy ions can escape earthward and tailward. There is a possibility that the dawnward flow consists of adjacent plasma sheet plasmas transported by the pressure gradient force at the duskside edge. The present results would be the first step to construct a three-dimensional structure of magnetic reconnection in various cosmic plasmas.