11:45 AM - 12:00 PM
[PEM14-22] Simultaneous observation of auroral substorm onset in Polar satellite global images and ground-based all-sky images
Keywords:substorm, auroral breakup, aurora, global image, all-sky image
We first identified the substorm onset brightening at 2127:49 UT in the global images and then searched for corresponding signatures in the all-sky images. The Akasofu initial brightening (2124:50 UT) and the poleward expansion (2127:50 UT) were observed in the all-sky images, indicating that the onset in global images was not simultaneous with the actual onset but rather with the poleward expansion in the all-sky images. The Akasofu initial brightening was not observed in the global images, which may possibly be attributed to the limited sensitivity of global images for thin auroral arc brightenings. This result suggests that substorm onset identified in global images does not necessarily represent the Akasofu substorm onset, but rather corresponds to the poleward expansion a few minutes later.