Title: Statistical study of auroral omega bands,
Abstract: The presence of very few statistical studies on auroral omega bands motivated
us to test-use a semi-automatic method for identifying large-scale undulations
of the diffuse aurora boundary and to investigate their occurrence. Five
identical all-sky cameras with overlapping fields of view provided data for 438
auroral omega-like structures over Fennoscandian Lapland from 1996 to 2007. The
results from this set of omega band events agree remarkably well with previous
observations of omega band occurrence in magnetic local time (MLT), lifetime,
location between the region 1 and 2 field-aligned currents, as well as current
density estimates. The average peak emission height of omega forms corresponds
to the estimated precipitation energies of a few keV, which experienced no
significant change during the events. Analysis of both local and global
magnetic indices demonstrates that omega bands are observed during substorm
expansion and recovery phases that are more intense than average substorm
expansion and recovery phases in the same region. The omega occurrence with
respect to the substorm expansion and recovery phases is in a very good
agreement with an earlier observed distribution of fast earthward flows in the
plasma sheet during expansion and recovery phases. These findings support the
theory that omegas are produced by fast earthward flows and auroral streamers,
despite the rarity of good conjugate observations.