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| Titel |
Velocity shear and current driven instability in a collisional F-region |
| VerfasserIn |
P. J. G. Perron, J.-M. A. Noël, J.-P. St.-Maurice |
| 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 ; 27, no. 1 ; Nr. 27, no. 1 (2009-01-23), S.381-394 |
| Datensatznummer |
250016379
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| Publikation (Nr.) |
 copernicus.org/angeo-27-381-2009.pdf |
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| Zusammenfassung |
| We have studied how the presence of collisions affects the behavior of
instabilities triggered by a combination of shears and parallel currents in
the ionosphere under a variety of ion to electron temperature ratios. To this
goal we have numerically solved a kinetic dispersion relation, using a
relaxation model to describe the effects of ion and electron collisions. We
have compared our solutions to expressions derived in a fluid limit which
applied only to large electron to ion temperature ratios. We have limited our
study to threshold conditions for the current density and the shears. We have
studied how the threshold varies as a function of the wave-vector angle
direction and as a function of frequency. As expected, we have found that for
low frequencies and/or elevated ion to electron temperature ratios, the
kinetic dispersion relation has to be used to evaluate the threshold
conditions. We have also found that ion velocity shears can significantly
lower the field-aligned threshold current needed to trigger the instability,
especially for wave-vectors close to the perpendicular to the magnetic field.
However the current density and shear requirements remain significantly
higher than if collisions are neglected. Therefore, for ionospheric
F-region applications, the effect of collisions should be included in
the calculation of instabilities associated with horizontal shears in the
vertical flow. Furthermore, in many situations of interest the kinetic
solutions should be used instead of the fluid limit, in spite of the fact
that the latter can be shown to produce qualitatively valid solutions. |
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