Omega bands

spaceweb@oulu.fi - last update: 11 May 1998, 1830 UT (RR)

Omega bands are large scale, discrete auroral folds or wavy structures that may sometimes develop into torch-like structures extending toward the pole (Akasofu and Kimball, 1964; Akasofu, 1974). Their main properties are:

They occur typically during the recovery phase of a substorm at the poleward boundary of a diffuse aurora (equatorward oval of the double oval structure typical for the recovery phase)
The size of the structures can vary from a few hundred to several thousand kilometers
They drift typically eastward at the velocity of 0.4 - 2 km/s (e.g., Opgenoorth et al., 1983), although torches have sometimes seen drifting also westward
The central regions of torch structures can be activity centers of pulsating auroras
The omega bands are accompanied by Ps 6 pulsations (T = 5 - 40 min)

For some recent modeling and observation of the omega bands, see Yamamoto et al. (1997) and Pulkkinen et al. (1998), respectively.

References

Akasofu, S.-I., A study of auroral displays photographed from the DMSP-2 satellite and from the Alaska meridian chain of stations, Space Sci. Rev., 16, 617-, 1974.
Akasofu, S.-I. and D. S. Kimball, The dynamics of aurora, 1, Instabilities of the aurora, J. Atmos. Terr. Phys., 26, 205-, 1964.
Opgenoorth, H., J. Oksman, K. U. Kaila, E. Nielsen, and W. Baumjohann, On the characteristics of eastward drifting omega bands in the morning sector, J. Geophys. Res., 88, 9171-9185, 1983.
Pulkkinen, T. I., D. N. Baker, L. A. Frank, J. B. Sigwarth, H. J. Opgenoorth, R. Greenwald, E. Friis-Christensen, T. Mukai, R. Nakamura, H. Singer, G. D. Reeves, and M. Lester, Two substorm intensifications compared: Onset, expansion, and global consequences, J. Geophys. Res., 103, 15-27, 1998.
Yamamoto, T., S. Inoue, and C.-I. Meng, Formation of auroral omega bands in the paired region 1 and region 2 field-aligned current system, J. Geophys. Res., 102, 2531-2544, 1997.