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Title: The spectral characteristics of E-region radar echoes co-located with and adjacent to visual auroral arcs
Authors: Milan, S. E.
Sato, N.
Lester, M.
Yeoman, T. K.
Murata, Y.
Doi, H.
Saemundsson, T.
First Published: 30-Jun-2002
Publisher: European Geosciences Union (EGU), Copernicus Publications, Springer Verlag (Germany)
Citation: Annales Geophysicae, 2002, 20 (6), pp. 795-805 (11)
Abstract: Simultaneous all-sky camera and HF radar observations of the visual and E-region radar aurora in the west-ward electrojet suggest a close relationship between a pair of parallel east-west-aligned auroral arcs, separated by ~ 30 km, and a region of strong radar backscatter. Poleward of this a broader region of radar backscatter is observed, though the spectral characteristics of the echoes in these two regions differ considerably. We suggest that the visual aurorae and their radar counterparts are produced in a region of upward field-aligned current (FAC), whereas the backscatter poleward of this is associated with downward FAC. Relatively low electric fields ( ~ 10 mV m^-1) are observed in the vicinity of the arc system, suggesting that in this case, two-stream waves are not directly generated through the electrodynamics of the arc. Rather, the generation of irregularities is most probably associated with the gradient drift instability operating within horizontal electron density gradients produced by the filamentary nature of the arc FAC system. The observation of high Doppler shift echoes superimposed on slow background flow within the region of backscatter poleward of the visual aurora is argued to be consistent with previous suggestions that the ion-acoustic instability threshold is reduced in the presence of upwelling thermal electrons carrying downward FAC.
DOI Link: 10.5194/angeo-20-795-2002
ISSN: 0992-7689
eISSN: 1432-0576
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: © Author(s) 2002. 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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