Time evolution of high-altitude plasma bubbles imaged at geomagnetic conjugate points

Temporal and spatial evolution of two high-altitude plasma bubbles (evening and midnight) was observed on 4 April 2002, at geomagnetic conjugate points at Sata, Japan (magnetic latitude 24degrees N), and Darwin, Australia (magnetic latitude 22degrees S), using two 630-nm airglow imagers. The apex height of the bubbles reached similar to1500km. The upward velocity of the evolution was faster in the evening (similar to170m/s at 20:00-21:00 LT) than around midnight (similar to28 m/s at 23:00-00:00 LT). Bifurcating features of the bubbles into a smaller scale size of similar to50 km were clearly seen for both the evening and midnight bubbles, showing fairly good conjugacy between the Northern and Southern Hemispheres.