|
|
 |
|
|
Ann. Geophys., 19, 189-204, 2001
www.ann-geophys.net/19/189/2001/
© European Geosciences Union 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)
Full Article in PDF (16545 KB) |
|
|
