Spatial extent and dynamics of a thin current sheet during the substorm growth phase on December 10, 1996

Multispacecraft observations are analyzed to examine the dynamics of thin c urrent sheet evolution during the early phases of a substorm during the per iod 0630-0800 UT on December 10, 1996, The ground signatures showed two act ivations, one latitudinally localized at 0731 UT and another, larger expans ion around 0800 UT. A local model consisting of two current sheets (a thin current sheet and a thicker plasma sheet) was developed utilizing two-space craft magnetic held measurements within the magnetotail. Extension of the t hin current sheet model to the inner magnetotail shows that during most of the growth phase, the thin current sheet intensified simultaneously and at the same fate in the mid- magnetotail (similar to 30 R-E) and near geosynch ronous orbit. These results show that a thin current sheet extended from th e near-geostationary region to the midtail, and that the entire current she et responded to the driving in a coherent way. Furthermore, timings suggest that the onset-associated disturbances were observable in the midtail befo re the ground or geosynchronous signatures.