Abstract
Abstract. We present synoptic observations of the 21 December 2006 substorm event by the THEMIS ground-based All-Sky-Imagers, the ISUAL CCD Imager aboard the FORMOSAT-2 satellite, the geosynchronous satellites and the ground-based magnetometers, and discuss the implication of the observations. There are three subsequent arc breakups with time separation of <1 min during the substorm expansion phase. In particular, we investigated the mode number of the substorm arc bead-like structure and the concurrent behavior of the arc intensity, the westward electroject intensity, and the ground Pi2 pulsation amplitude. Prior to each arc breakup there was a clear azimuthally-spaced bright spot structure along the arc with high mode number (~140–180) and the arc intensity increased together with the westward electrojet and the ground Pi2 pulsation amplitude under the arc. The Pi1 perturbations observed under the arc appeared at or after the arc breakup started. This suggests that the Pi2 pulsation is related to the arc formation. The Pi2 pulsation may be caused by the kinetic ballooning instability (KBI) that is excited in the strong cross-tail current region. The longitudinal extent of the earthward expansion front of the substorm dipolarization region at the geosynchronous orbit is estimated from timings of the energetic proton and electron injections and is roughly located between ~19.50 MLT and ~23.00 MLT, which is consistent with the corresponding longitudinal extent of the auroral substorm activity.
Highlights
Decades of research have demonstrated that the substorm is a significant dynamical process of energy storage and release in the magnetosphere and ionosphere
In this study we have presented the main observational features of an auroral substorm event occurred on 21 December 2006
A faint aurora appeared on the equatorward side of the pre-existing arc at 08:26:36 UT and propagated westward to the edge of KIAN FOV when the substorm initiation arc was observed at ∼08:27:09 UT on the equatorward side latitude of the faint aurora
Summary
Decades of research have demonstrated that the substorm is a significant dynamical process of energy storage and release in the magnetosphere and ionosphere. Because the growth of substorm arcs typically lasts ∼1–3 min or shorter prior to breakup and the arcs have bright spot structure of
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