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| Titel |
Observations of day-to-day variability in precursor signatures to equatorial F-region plasma depletions |
| VerfasserIn |
P. R. Fagundes, Y. Sahai, I. S. Batista, M. A. Abdu, J. A. Bittencourt, H. Takahashi |
| 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 ; 17, no. 8 ; Nr. 17, no. 8, S.1053-1063 |
| Datensatznummer |
250013799
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| Publikation (Nr.) |
 copernicus.org/angeo-17-1053-1999.pdf |
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| Zusammenfassung |
In December 1995, a campaign was carried out
to study the day-to-day variability in precursor signatures to large-scale
ionospheric F-region plasma irregularities, using optical diagnostic techniques,
near the magnetic equator in the Brazilian sector. Three instruments were
operated simultaneously: (a) an all-sky (180° field of view) imaging system for
observing the OI 630 nm nightglow emission at Alc-ntara (2.5°S, 44.4°W); (b)
a digisonde (256-Lowell) at São Luis (2.6°S, 44.2°W); and (c) a multi-channel
tilting filter-type zenith photometer for observing the OI 630 nm and
mesospheric nightglow emissions at Fortaleza (3.9°S, 38.4°W). During the
period December 14-18, 1995 (summer in the southern hemisphere), a good sequence
of the OI 630 nm imaging observations on five consecutive nights were obtained,
which are presented and discussed in this study. The observing period was
geomagnetically quiet to moderate
(Kp = 0+ to 5+; Dst = 18 nT to -37 nT). On four nights, out of the
five observation nights, the OI 630 nm imaging pictures showed formations of
transequatorial north-south aligned intensity depletions, which are the optical
signatures of large-scale ionospheric F-region plasma bubbles. However,
considerable day-to-day variability in the onset and development of the plasma
depleted bands was observed. On one of the nights it appears that the rapid
uplifting of the F-layer in the post-sunset period, in conjunction with gravity
wave activity at mesospheric heights, resulted in generation of very strong
plasma bubble irregularities. One of the nights showed an unusual formation of
north-south depleted band in the western sector of the imaging system field of
view, but the structure did not show any eastward movement, which is a normal
characteristic of plasma bubbles. This type of irregularity structure, which
probably can be observed only by wide-angle imaging system, needs more
investigations for a better understanding of its behaviour.
Key words. Atmospheric composition and structure
(airglow and aurora) · Ionosphere (equatorial ionosphere; ionospheric
irregularities) |
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