Previous studies of auroral behaviors have suggested that the substorm expansion is a result of a chain of processes originating in the magnetotail. We present a detailed study on the substorm expansion behavior on 3 November 1998, using the global auroral images from Polar and the conjugate central plasma sheet data from Geotail in the near-Earth tail. The closer inspection of the auroral data enables us to characterize the stepwise feature of the auroral evolution, which were found to be spatially and temporally separable into two intense auroral activities: the initial brightening of the substorm arc and the second aurora that took place eastward of the first one with the time delay of 4.5 min. Comparing the near-Earth tail observation of the fast plasma flow, we show that the observed time lag of 4.5 min can be explained by a systematic chain of plasma processes in the central plasma sheet, indicating that this time delay can be interpreted as a generic behavior. The generality of the stepwise evolution within the expected time lag of 2-6 min is also pursued, and is found for three out of six substorms. With respect to the stepwise feature, our observation of six substorms suggests that there are at least three types of substorm expansion dynamics that are attributable to different chains of tail processes.
