Statistical and case studies of 2fce auroral roar observed with a medium frequency interferometer

The medium frequency interferometer (MFI) is the first direction-sensitive instrument to observe auroral radio emissions in the frequency range 2500-3000 kHz. The MFI has observed many auroral roar events since operations began at the Sondrestrom Research Facility near Kangerlussuaq, Greenland, in April 1999. The MFI data reveal that individual auroral roar events often propagate to the MFI from multiple directions and that the source locations show interesting time-variable features such as drifting and oscillations with a period of a few minutes in both azimuth and zenith angles. Most events have a direction of arrival from the local magnetic south, with the latitude distribution of the apparent source regions peaked near the poleward edge of the statistical auroral oval. The altitude distribution of apparent source locations has a bimodal form, which may be interpreted as evidence for two distinct well-separated sources, one on the topside F region and one on the bottomside.