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| Titel |
The electron drift velocity, ion acoustic speed and irregularity drifts in high-latitude E-region |
| VerfasserIn |
M. V. Uspensky, R. J. Pellinen, P. Janhunen  |
| 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 ; 26, no. 11 ; Nr. 26, no. 11 (2008-10-24), S.3395-3409 |
| Datensatznummer |
250016280
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| Publikation (Nr.) |
 copernicus.org/angeo-26-3395-2008.pdf |
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| Zusammenfassung |
| The purpose of this study is to examine the STARE irregularity drift
velocity dependence on the EISCAT line-of-sight (los or l-o-s) electron
drift velocity magnitude, VE×Blos, and the flow angle ΘN,F (superscript N and/or F refer to the STARE Norway and Finland
radar). In the noon-evening sector the flow angle dependence of Doppler
velocities, VirrN,F, inside and outside the Farley-Buneman (FB)
instability cone (|VE×Blos|>Cs and |VE×Blos|<Cs, respectively, where Cs is the ion
acoustic speed), is found to be similar and much weaker than suggested
earlier. In a band of flow angles 45°<ΘN,F<85° it
can be reasonably described by |VirrN,F|∝AN,FCscosnΘN,F, where AN,F≈1.2–1.3 are
monotonically increasing functions of VE×B and the index n is ~0.2
or even smaller. This study (a) does not support the conclusion by
Nielsen and Schlegel (1985), Nielsen et al. (2002, their #[18]) that at
flow angles larger than ~60° (or |VirrN,F|≤300 m/s) the STARE Doppler velocities are equal to the
component of the electron drift velocity. We found (b) that if the data
points are averages over 100 m/s intervals (bins) of l-o-s electron
velocities and 10 deg intervals (bins) of flow angles, then the largest
STARE Doppler velocities always reside inside the bin with the largest flow
angle. In the flow angle bin 80° the STARE Doppler velocity is larger than
its driver term, i.e. the EISCAT l-o-s electron drift velocity component,
|VirrN,F|>|VE×Blos|. Both
features (a and b) as well as the weak flow angle velocity dependence
indicate that the l-o-s electron drift velocity cannot be the sole factor
which controls the motion of the backscatter ~1-m irregularities at
large flow angles. Importantly, the backscatter was collected at aspect
angle ~1° and flow angle Θ>60°, where linear fluid and
kinetic theories invariably predict negative growth rates. At least
qualitatively, all the facts can be reasonably explained by nonlinear
wave-wave coupling found and described by Kudeki and Farley (1989), Lu et
al. (2008) for the equatorial electrojet and studied in numerical simulation
by Otani and Oppenheim (1998, 2006). |
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