Further investigation of auroral roar fine structure

In April 1996, a downconverting receiver was operated in Churchill, Manitoba, Canada, to increase the statistics about the recently discovered fine structure of auroral roar emissions. Auroral roar is found to be both structured and unstructured., A wide variety of previously unknown tonal features drifting in a complicated manner were recorded. These structured features can be classified according to their duration, frequency dl:ift, and grouping with like features. Typically, 95% of the structured features last less than 1 s. The slope of drifting features is more commonly negative than positive with a magnitude typically less than a few kHz s(-1) and a maximum of similar to 800 kHz s(-1). The minimum bandwidth of features is 6 Hz or less, and typical separation between similar features is similar to 400 Hz. These measurements form a basis for reviewing proposed generation mechanisms of auroral roar including a localized source model and laser cavity mechanism.