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Ann. Geophys., 19, 205-217, 2001
www.ann-geophys.net/19/205/2001/
© European Geosciences Union 2001
On the altitude dependence of the spectral characteristics of decametre-wavelength E region backscatter and the relationship with optical auroral forms
S. E. Milan1, M. Lester1, N. Sato2, and H. Takizawa3
1Department of Physics and Astronomy, Leicester University, Leicester LE1 7RH, UK
2National Institute of Polar Research, Tokyo 173, Japan
3Tohoku University, Sendai 980–8578, Japan
Correspondence to: S. Milan (Steve.Milan@ion.le.ac.uk)
Abstract. Observations of E region
backscatter by the Ice-land East SuperDARN HF radar from the 30 minute period
2330 to 2400 UT on 13 September 1999 are presented, along with simultaneous
observations of auroral luminosity from two all-sky cameras. Interferometric
techniques are employed to estimate the altitude of origin of each echo observed
by the radar. Under investigation is a region of backscatter which is L-shell
aligned and exists in a region of low auroral luminosity bounded to the north
and the south by two auroral arcs. The spectral characteristics of the
backscatter fall into three main populations: broad, low Doppler shift spectra;
narrow, high Doppler shift spectra; and exceptionally narrow, low Doppler shift
spectra. The first two populations are similar to type II and type I spectra
observed with VHF radars, respectively. These populations scatter from near the
peak of the E region. The high Doppler shift population appears to exist in a
region of sub-critical electric field. The third population originates below the
E region peak at altitudes between 80 and 100 km. We argue that a non-coherent
scattering process is responsible for this backscatter.
Key words. Ionosphere (auroral ionosphere; ionospheric
irregularities)
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