Reconnection Hall current system observed in the magnetotail and in the ionosphere

On 07 Sep 2001 around 21:40 UT, Cluster was located 19~R_E downtail, and observed earthward fast flows and strong perturbations in the dawn-dusk component of the magnetic field (B_Y). The perturbations corresponded to a sheet of tailward field aligned current close to the neutral sheet and another sheet of earthward field aligned current closer to the lobe. At Cluster footpoint, the ionospheric equivalent current density was monitored by the IMAGE magnetometer network. The observed equivalent current pattern is found to be consistent with a longitudinally extended current out of the ionosphere at 67^o magnetic latitude and another sheet into the ionosphere 10~km further north. These observations provide evidence that the Hall current system generated in the ion diffusion region of a tail reconnection X-line, can close in the ionosphere.