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 drift, 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
and a maximum of
800 kHz s. The minimum bandwidth of features
is 6 Hz or less, and typical separation between similar
features is 400 Hz. These measurements form a basis
for reviewing proposed generation mechanisms of auroral
roar including a localized source model and laser cavity
mechanism.
AGU Index Terms: 2407 Auroral Ionosphere; 2471 Plasma waves and instabilities; 2704 Auroral phenomena; 2772 Plasma waves and instabilities
Keywords/Free Terms: Fine structure, auroral roar, HF emissions, Radio waves
JGR-Space 97JA03171
Vol. 103
, No. A2
, p. 2219