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Fig. 5 | Earth, Planets and Space

Fig. 5

From: Simultaneous observation of auroral substorm onset in Polar satellite global images and ground-based all-sky images

Fig. 5

Ground-based all-sky images (ASIs) near the substorm onset location on December 7, 1999. Auroral brightness at a wavelength of 557.7 nm (green-line) observed at Muonio (MUO) in Finland is shown. a Selected images that represent three intervals as labeled, shown in the geodetic coordinates. The white reference lines represent MLTs and MLATs. The red line indicates 23.2 MLT, the approximate location of the initiation of the Akasofu initial brightening (AIB) and the poleward expansion. b Auroral keograms sliced along the onset meridian (23.2 MLT, ± 0.2 h average), which correspond to the red lines in a. c Time series of auroral brightness near the onset location (23.2 MLT, 64.6 MLAT), averaged over 23.0–23.4 MLT and 64.5–64.7 MLAT. The red vertical lines in b and c indicate the times of the AIB (2124:50 UT) and the poleward expansion (2127:50 UT) in the ASIs

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