Please use this identifier to cite or link to this item: http://hdl.handle.net/2381/39439
Title: Multi-frequency observations of E-region HF radar aurora
Authors: Milan, S. E.
Lester, M.
Sato, N.
First Published: 31-Mar-2003
Publisher: European Geosciences Union (EGU), Copernicus Publications, Springer Verlag (Germany)
Citation: Annales Geophysicae, 2003, 21 (3), pp. 761-777 (17)
Abstract: Multi-frequency observations of E-region coherent backscatter from decametre waves reveal that auroral echoes tend to comprise two spectral components superimposed, one at low Doppler shifts, below 250 ms-1, and the other Doppler shifted to near the ion-acoustic speed or above, up to 800 ms-1. The low Doppler shift component occurs at all look directions; Doppler shifts near the ion acoustic speed occur when looking at low flow angles along the direction of the electron drift in the electrojet, and Doppler shifts in excess of the ion acoustic speed occur at intermediate flow angles. The latter population appears most commonly at radar frequencies near 10–12 MHz, with its occurrence decreasing dramatically at higher frequencies. The velocity of the high Doppler shift echoes increases with increasing radar frequency, or irregularity wave number k. The velocity of the low Doppler shift population appears to be suppressed significantly below the line-of-sight component of the electron drift. Initial estimates of the altitude from which scatter occurs suggest that the high Doppler shift echoes originate from higher in the E-region than the low Doppler shift echoes, certainly in the eastward electrojet. We discuss these observations with reference to the theories of de/stabilization of two-stream waves by electron density gradients and electrostatic ion cyclotron waves excited by field-parallel electron drifts.
DOI Link: 10.5194/angeo-21-761-2003
ISSN: 0992-7689
eISSN: 1432-0576
Links: http://www.ann-geophys.net/21/761/2003/
http://hdl.handle.net/2381/39439
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: © Author(s) 2003. This work is distributed under the Creative Commons Attribution 3.0 License.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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