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| Titel |
Observations and modeling of post-midnight uplifts near the magnetic equator |
| VerfasserIn |
M. J. Nicolls, M. C. Kelley, M. N. Vlasov, Y. Sahai, J. L. Chau, D. L. Hysell, P. R. Fagundes, F. Becker-Guedes, W. L. C. Lima |
| 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 ; 24, no. 5 ; Nr. 24, no. 5 (2006-07-03), S.1317-1331 |
| Datensatznummer |
250015549
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| Publikation (Nr.) |
 copernicus.org/angeo-24-1317-2006.pdf |
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| Zusammenfassung |
| We report here on post-midnight uplifts near the magnetic equator. We present
observational evidence from digital ionosondes in Brazil, a digisonde in
Peru, and other measurements at the Jicamarca Radio Observatory that show
that these uplifts occur fairly regularly in the post-midnight period,
raising the ionosphere by tens of kilometers in the most mild events and by
over a hundred kilometers in the most severe events. We show that in general
the uplifts are not the result of a zonal electric field reversal, and
demonstrate instead that the uplifts occur as the ionospheric response to a
decreasing westward electric field in conjunction with sufficient
recombination and plasma flux. The decreasing westward electric field may be
caused by a change in the wind system related to the midnight pressure bulge,
which is associated with the midnight temperature maximum. In order to agree
with observations from Jicamarca and Palmas, Brazil, it is shown that there
must exist sufficient horizontal plasma flux associated with the pressure
bulge. In addition, we show that the uplifts may be correlated with a
secondary maximum in the spread-F occurrence rate in the post-midnight
period. The uplifts are strongly seasonally dependent, presumably according
to the seasonal dependence of the midnight pressure bulge, which leads to the
necessary small westward field in the post-midnight period during certain
seasons. We also discuss the enhancement of the uplifts associated with
increased geomagnetic activity, which may be related to disturbance dynamo
winds. Finally, we show that it is possible using simple numerical techniques
to estimate the horizontal plasma flux and the vertical drift velocity from
electron density measurements in the post-midnight period. |
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