Multi-instrument observations of the electric and magnetic field structureof omega bands

High time resolution data from the CUTLASS Finland radar during the interva l 01:30-03:30 UT on 11 May, 1998, are employed to characterise the ionosphe ric electric field due to a series of omega bands extending similar to 5 de grees in latitude at a resolution of 45 km in the meridional direction and 50 km in the azimuthal direction. E-region observations from the STARE Norw ay VHF radar operating at a resolution of 15 km over a comparable region ar e also incorporated. These data are combined with ground magnetometer obser vations from several stations. This allows the study of the ionospheric equ ivalent current signatures and height integrated ionospheric conductances a ssociated with omega bands as they propagate through the field-of-view of t he CUTLASS and STARE radars. The high-time resolution and multi-point natur e of the observations leads to a refinement of the previous models of omega band structure. The omega bands observed during this interval have scale s izes similar to 500 km and an eastward propagation velocity similar to 0.75 km s(-1). They occur in the morning sector (similar to 05 MLT), simultaneo usly with the onset/intensification of a substorm to the west during the re covery phase of a previous substorm in the Scandinavian sector. A possible mechanism for omega band formation and their relationship to the substorm p hase is discussed.