Evidence for component merging near the subsolar magnetopause: Geotail observations

On January 29, 1996, the Geotail satellite skimmed inside the magnetopause from the morningside to the subsolar region and observed multiple magnetopause crossings near the subsolar region (∼1100-1200 local time). Geotail observed accelerated northward (southward) flows accompanied by duskward (dawnward) flows at the magnetopause and/or in the boundary layer near the subsolar region. Such accelerated flows are qualitatively and quantitatively consistent with the theoretical predictions for reconnection. These events were observed when the interplanetary magnetic field (IMF) was steady and was directed southward (B_z < 0)/dawnward (B_y < 0). The amplitude of the IMF B_y was larger than that of the IMF B_z. The accelerated flow reversals near the subsolar region may be interpreted by the motion (i.e., slightly moving up and down) of the reconnection line, which tilts from the north-dawn quadrant to the south-dusk quadrant and passes through the subsolar point, with respect to the satellite. We suggest that our observations can be taken as evidence for the component merging model.