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| Titel |
STARE velocities: 2. Evening westward electron flow |
| VerfasserIn |
M. Uspensky, A. Koustov, P. Janhunen  , E. Nielsen, K. Kauristie, O. Amm, R. Pellinen, H. Opgenoorth, R. Pirjola |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 22, no. 4 ; Nr. 22, no. 4 (2004-04-02), S.1077-1091 |
| Datensatznummer |
250014824
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| Publikation (Nr.) |
 copernicus.org/angeo-22-1077-2004.pdf |
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| Zusammenfassung |
Four evening events and one morning event of joint EISCAT/STARE observations during
~22h are considered and the differences between observed STARE line-of-sight
(l-o-s) velocities and EISCAT electron drift velocities projected onto the STARE beams are
studied. We demonstrate that the double-pulse technique, which is currently in use in
the STARE routine data handling, typically underestimates the true phase velocity as
inferred from the multi-pulse STARE data. We show that the STARE velocities are
persistently smaller (1.5–2 times) than the EISCAT velocities, even for the multi-pulse
data. The effect seems to be more pronounced in the evening sector when the Finland
radar observes at large flow angles. We evaluate the performance of the ion-acoustic
approach (IAA, Nielsen and Schlegel, 1985) and the off-orthogonal fluid approach
(OOFA, Uspensky et al., 2003) techniques to predict the true electron drift velocity for
the base event of 12 February 1999. The IAA technique predicts the convection
reasonably well for enhanced flows of >~1000m/s, but not so well for slower ones. By
considering the EISCAT N(h) profiles, we derive the effective aspect angle and
effective altitude of backscatter, and use this information for application of the OOFA
technique. We demonstrate that the OOFA predictions for the base event are superior
over the IAA predictions and thus, we confirm that OOFA predicts the electron
velocities reasonably well in the evening sector, in addition to the morning sector, as
concluded by Uspensky et al. (2003). To check how "robust" the OOFA model is and
how successful it is for convection estimates without the EISCAT support, we analysed
three additional evening events and one additional morning event for which information on N(h)
profiles was intentionally ignored. By accepting the mean STARE/EISCAT velocity
ratio of 0.55 and the mean azimuth rotation of 9° (derived for the basic event), we
show that the OOFA performs reasonably well for these additional events.
Key words. Ionosphere (ionospheric irregularities, plasma
waves and instabilities, auroral ionosphere) |
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