  We present three eastward-expanding auroral surge (EEAS) events that were
observed intermittently at intervals of about 15 min in the post-midnight
sector (01:55-02:40 MLT) by all-sky imagers and magnetometers in northern
Europe. It was deduced that each surge occurred just after each onset of a
multiple-onset substorm, which was small-scale and did not clearly expand
westward, because they were observed almost simultaneously with Pi 2 pulsations
at the magnetic equator and magnetic bay variations at middle-to-high latitudes
associated with the DP-1 current system. The EEASs showed similar properties to
omega bands or torches reported in previous studies, such as recurrence
intervals of about 15 min, concurrence with magnetic pulsations with amplitudes
of several tens of nanotesla, horizontal scales of 300-400 km, and occurrence
of a pulsating aurora in a diffuse aurora after the passage of the EEASs.
Furthermore, the EEASs showed similar temporal evolution to the omega bands,
during which eastward-propagating auroral streamers occurred simultaneously in
the poleward region, followed by the formation of north-south-aligned auroras,
which eventually connected with the EEASs. Thus, we speculate that EEASs may be
related to the generation process of omega bands. (Continued)
