Field-aligned currents associated with dipolarization fronts

Abstract

Current densities associated with dipolarization fronts (DFs) have been calculated in the geomagnetic tail using the curlometer technique applied to high-resolution magnetic field B→ data obtained by the four Cluster spacecraft. We then use the relation b→·×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/m2, and they are observed in Northern and Southern Hemispheres flowing along both directions of the B→-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 Bz dips). Most of our observations come from 15 to 20 RE in the tail, different from previous statistical studies based mainly on observations made around 9-12 RE. We suggest that DFs can sustain significant FACs and appear as "wedgelets" in the early stage. Key Points The DFs sustain significant FACs and appear as wedgelets in the early stage Only the DFs with magnetic dips correspond with the region-2 sense FACs This work is case study and the calculations are more accurate ©2013. American Geophysical Union. All Rights Reserved.