FAST Observations of the Formation of the Cold Dense Plasma Sheet

FAST observations during extended periods of northward IMF provide a global picture of the formation of the Cold Dense Plasma Sheet (CDPS). These observations suggest that dual lobe reconnection, as described by Song and Russell (JGR, 1992), is the most likely source of the CDPS. One aspect of dual lobe reconnection that has not been appreciated is the dual injection of ions at both lobe reconnection sites. These ions continue to bounce-drift with the flux tube forming velocity dispersed ion signatures (VDIS) that continue around the flanks of the auroral oval. These bouncing ions have a signature with energy increasing with latitude, and form overlapping dispersive signatures as the flux tubes convect to the nightside. These observations suggest that most of the VDIS signatures observed by sounding rockets and satellites away from the cusp are actually cusp injections after several bounces. In addition, a VDIS near the cusp does not necessarily indicate the flux tube just reconnected since the observer may be seeing ions that have bounced. These results suggest that mechanisms involving impulsive ion penetration or flank magnetopause ion injections may be unnecessary to describe these VDIS signatures.