SPRG Seminars
May 1, 2012:
"The Properties of the Dipolarization Front Current Sheet: Statistics "
Jiang Liu, IGPP, UCLA
A Dipolarizing flux bundle (DFB) is the large positive Bz region bounded by the dipolarization front (DF). The dipolarization front current sheet (DFCS) is responsible for the strong Bz inside the DFB and the Bz dip signature ahead of the DF. We build a DFB event list from THEMIS’s four tail season observations. Based on this event list, we use a variety of orientation analysis techniques to deduce the DFCS’s topology and its spatial variation on thickness, current direction and strength. In a statistical sense, the DFCS’s projection in the XZ plane has an ordinary magnetic field line’s shape; the DFCS’s transverse section in the XY plane has a round head, consistent with previous case studies and simulations. The DFCS currents are perpendicular to the magnetic field close to the neutral sheet; they divert into field-aligned currents (FACs) farther away from the neutral sheet and are in the region-1 sense. To the zero-th order, the DFCS thins and strengthens close to the neutral sheet; its current is more intense closer to its sagittal center. To a higher order, the DFCS thickness and current density exhibits a dip at the neutral sheet; its current abundance also has a dip at the DF head point. We also found that DFBs are usually accompanied by cross-tail current sheet thickening and reduction.