Journal cover Journal topic
Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 19, 189-204, 2001
http://www.ann-geophys.net/19/189/2001/
doi:10.5194/angeo-19-189-2001
© Author(s) 2001. This work is distributed
under the Creative Commons Attribution 3.0 License.
 
28 Feb 2001
A classification of spectral populations observed in HF radar backscatter from the E region auroral electrojets
S. E. Milan and M. Lester Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
Correspondence to: S. E. Milan (steve.milan@ion.le.ac.uk)
Abstract. Observations of HF radar backscatter from the auroral electrojet E region indicate the presence of five major spectral populations, as opposed to the two predominant spectral populations, types I and II, observed in the VHF regime. The Doppler shift, spectral width, backscatter power, and flow angle dependencies of these five populations are investigated and described. Two of these populations are identified with type I and type II spectral classes, and hence, are thought to be generated by the two-stream and gradient drift instabilities, respectively. The remaining three populations occur over a range of velocities which can greatly exceed the ion acoustic speed, the usual limiting velocity in VHF radar observations of the E region. The generation of these spectral populations is discussed in terms of electron density gradients in the electrojet region and recent non-linear theories of E region irregularity generation.

Key words. Ionosphere (ionospheric irregularities)


Citation: Milan, S. E. and Lester, M.: A classification of spectral populations observed in HF radar backscatter from the E region auroral electrojets, Ann. Geophys., 19, 189-204, doi:10.5194/angeo-19-189-2001, 2001.
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