First observations of 5fce auroral roars
Article first published online: 13 OCT 2012
©2012. American Geophysical Union. All Rights Reserved.
Geophysical Research Letters
Volume 39, Issue 19, 16 October 2012
How to Cite
2012), First observations of 5fce auroral roars, Geophys. Res. Lett., 39, L19106, doi:10.1029/2012GL053551.(
- Issue published online: 13 OCT 2012
- Article first published online: 13 OCT 2012
- Manuscript Revised: 12 SEP 2012
- Manuscript Accepted: 12 SEP 2012
- Manuscript Received: 11 AUG 2012
- National Science Foundation. Grant Numbers: ANT-1141817, ANT-1043230
- plasma waves;
- radio emissions
 Auroral radio emissions reveal physics of beam-plasma interactions and provide possibilities to remotely sense ionospheric plasma processes.Sato et al. (2012) recently discovered that auroral roar emissions, long known to occur at two and three times the electron gyrofrequency (fce), also occur at 4fce. Using data from wave receivers in the British Antarctic Survey Automatic Geophysical Observatories, we confirm the existence of 4fce-roars and observe for the first time 5fce-roars. A search at higher frequencies did not find higher harmonics. Both 4fce- and 5fce-roars only occur in sunlit conditions near summer solstice. Harmonic roar emission frequencies scale with the strength of the geomagnetic field, and combining data from four observatories suggests that the 4fce-roar source height lies around 245 km, lower than the 275 km estimated for 2fce-roar. These observations show that the auroral roar generation mechanism acts under a broader set of plasma conditions than previously considered.