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Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 35, 1069-1083, 2017
https://doi.org/10.5194/angeo-35-1069-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Regular paper
07 Sep 2017
Statistical study of auroral omega bands
Noora Partamies1,4, James M. Weygand2, and Liisa Juusola3 1Department of Arctic Geophysics, University Centre in Svalbard, Longyearbyen, Norway
2University of Los Angeles, Department of Earth, Planetary and Space Sciences, California, USA
3Finnish Meteorological Institute, Earth Observations, Helsinki, Finland
4Birkeland Centre for Space Science, Norway
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.

Citation: Partamies, N., Weygand, J. M., and Juusola, L.: Statistical study of auroral omega bands, Ann. Geophys., 35, 1069-1083, https://doi.org/10.5194/angeo-35-1069-2017, 2017.
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Large-scale undulations of the diffuse aurora boundary, auroral omega bands, have been studied based on 438 omega-like structures identified over Fennoscandian Lapland from 1996 to 2007. The omegas mainly occurred in the post-magnetic midnight sector, in the region between oppositely directed ionospheric field-aligned currents, and during substorm recovery phases. The omega bands were observed during substorms, which were more intense than the average substorm in the same region.
Large-scale undulations of the diffuse aurora boundary, auroral omega bands, have been studied...
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