Field‐aligned currents associated with dipolarization fronts

Current densities associated with dipolarization fronts (DFs) have been calculated in the geomagnetic tail using the curlometer technique applied to high‐resolution magnetic fieldB → data obtained by the four Cluster spacecraft. We then use the relationb →· ∇ × B →to characterize the behavior of field‐aligned current (FAC) during 25 DF events. Our results show that the magnitude of FAC density ( J // ) ranges from 5 to 20 nA/m 2 , and they are observed in Northern and Southern Hemispheres flowing along both directions of theB → ‐field. The FACs have dimensions characteristic of the DFs and with region‐1 current sense flowing inside the DFs and region‐2 sense just in front of DF (in the B z dips). Most of our observations come from 15 to 20 R E in the tail, different from previous statistical studies based mainly on observations made around 9–12 R E . We suggest that DFs can sustain significant FACs and appear as “wedgelets” in the early stage.