Statistical study of auroral omega bands

TL;DR

This study statistically analyzes auroral omega bands using all-sky camera data, confirming their occurrence during intense substorm phases and supporting the theory that they are produced by fast earthward plasma flows.

Contribution

It introduces a semi-automatic method for identifying auroral omega bands and provides the first extensive statistical analysis of their occurrence and characteristics.

Findings

Omega bands occur during intense substorm phases.

Average peak emission height corresponds to a few keV precipitation energies.

Omega occurrence aligns with fast earthward plasma flows during substorms.

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.