Statistical and case studies of 2f(ce) auroral roar observed with a mediumfrequency interferometer

The medium frequency interferometer (MFI) is the first direction-sensitive instrument to observe auroral radio emissions in the frequency range 2500-3 000 kHz. The MFI has observed many auroral roar events since operations beg an at the Sondrestrom Research Facility near Kangerlussuaq, Greenland, in A pril 1999. The MFI data reveal that individual auroral roar events often pr opagate to the MFI from multiple directions and that the source locations s how interesting time-variable features such as drifting and oscillations wi th 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 latitu de distribution of the apparent source regions peaked near the poleward edg e of the statistical auroral oval. The altitude distribution of apparent so urce 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 o n the bottomside.