Abstract
Interhemispheric conjugate auroral features during a weak substorm interval were investigated using simultaneous all‐sky camera (ASC) measurements at the northern and southern geomagnetic conjugate points at Tjörnes (TJO; 66.2°N, 342.9°E) in Iceland and Syowa Station (SYO; 69.0°S, 39.6°E) in Antarctica. Around postmidnight, just after the substorm onset, the ASC field of view (FOV) at TJO was first filled with dynamic auroral activations; however, its counterpart was not detected over the zenith at SYO at that time. In contrast, in the late stage (about 20 min after the onset) of substorm development we observed spiral‐like auroral arcs with a similar shape drifting eastward across the center of each ASC FOV, although the one at TJO preceded the one at SYO. The time sequence of the interhemispheric conjugate auroral features was well reflected in the geomagnetic field variations at both stations. On the basis of a detailed comparison of both ASC images, we identified that the northern geomagnetic footprint of SYO was displaced poleward of TJO by up to 3.0° or more in the initial stage of substorm development, whereas in the late stage it was displaced eastward by up to ∼1 h relative to TJO and then moved closer to TJO. We emphasize that the dynamic motion of the conjugate points is a consequence of the time‐dependent magnetotail field reconfiguration process, controlled by the varying interplanetary magnetic field By polarity.
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