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| Titel |
Gravity wave initiation of equatorial spread F/plasma bubble irregularities based on observational data from the SpreadFEx campaign |
| VerfasserIn |
M. A. Abdu, E. Alam Kherani, I. S. Batista, E. R. Paula, D. C. Fritts, J. H. A. Sobral |
| 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. 7 ; Nr. 27, no. 7 (2009-07-01), S.2607-2622 |
| Datensatznummer |
250016574
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| Publikation (Nr.) |
 copernicus.org/angeo-27-2607-2009.pdf |
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| Zusammenfassung |
| The data from ground based experiments conducted during
the 2005 SpreadFEx campaign in Brazil are used, with the help of theoretical
model calculations, to investigate the precursor conditions, and especially,
the role of gravity waves, in the instability initiation leading to
equatorial spread F development. Data from a digisonde and a 30 MHz coherent
back-scatter radar operated at an equatorial site, Sao Luis (dip angle:
2.7°) and from a digisonde operated at another equatorial site (dip
angle: −11.5°) are analyzed during selected days representative of
differing precursor conditions of the evening prereversal vertical drift, F
layer bottom-side density gradients and density perturbations due to gravity
waves. It is found that radar irregularity plumes indicative of topside
bubbles, can be generated for precursor vertical drift velocities exceeding
30 m/s even when the precursor GW induced density oscillations are marginally
detectable by the digisonde. For drift velocities ≤20 m/s the presence of
precursor gravity waves of detectable intensity is found to be a necessary
condition for spread F instability initiation. Theoretical model
calculations show that the zonal polarization electric field in an
instability development, even as judged from its linear growth phase, can be
significantly enhanced under the action of perturbation winds from gravity
waves. Comparison of the observational results with the theoretical model
calculations provides evidence for gravity wave seeding of equatorial spread
F. |
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