HIGH-LATITUDE UNSTRUCTURED PC1 EMISSIONS GENERATED IN THE VICINITY OF THE DAYSIDE AURORAL OVAL

Three months of ground-based recordings of high latitude dayside Pc1 magnetic variations at auroral oval stations Syowa (MLAT = 67-degrees) and Mawson (MLAT = 70-degrees) are compared. Dynamic spectra reveal that banded unstructured Pc1 emissions (0.2-0.4 Hz) may be separated into pre-noon and post-noon activity. Although the pre-noon activity is common at Mawson, its observation at Syowa is associated with low altitude cleft-like ions being present at lower than normal latitudes, i.e. 75-degrees MLAT. These ions are determined from DMSP satellite observations. The Pc1 emissions at both stations are interpreted as arising from ion cyclotron waves generated in the equatorial plasmatrough region. We regard the dayside cleft as the free energy source of the pre-noon Pc1 activity by supplying the equatorial magnetosphere with ions. It is believed that the ion cyclotron waves enter the ionosphere within the auroral oval, poleward of Mawson and Syowa, and fast Alfven mode waves, which then arise, propagate to the stations in the F2-region ionospheric waveguide.