Coupling between substorms and ULF disturbances at polar latitudes

The trans-Antarctic search-coil magnetometer network has been used to study a possible coupling between the nighttime substorm activity and the behavior of ULF pulsations in the dayside cusp and nightside polar cap in frequency bands from Pc5/Pi2 to Pc2/Pil. During the summer period January-March 1997 11 substorms with steep onsets as observed at station AGO P3 have been analyzed. The data analysis has indicated a global coherency in the dynamics of substorm expansion and displayed unanticipated features in ULF wave activity. The extension of breakup-related ULF noises deep into the polar cap, up to latitudes 87 degrees has been observed. Trans-polar transmission of ULF waves from the dayside cusp region across the pole to 85 degrees could be seen. Simultaneous enhancement of ULF wave activity on the nightside and in the dayside cusp/mantle has been revealed during breakup. The observations also indicated the occurrence in the dayside cusp of a wave "substorm precursor" in the Pc4-5 frequency bands. Probably, long-period turbulence in the dayside boundary layers and lobe may stimulate the expansion phase of substorm