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Ann. Geophys., 22, 15-23, 2004
www.ann-geophys.net/22/15/2004/
© European Geosciences Union 2004
Generation of large-scale equatorial F-region plasma depletions during lowrange spread-F season
Y. Sahai1, P. R. Fagundes1, J. R. Abalde1, A. A. Pimenta2, J. A. Bittencourt2, Y. Otsuka3, and V. H. Rios4
1Universidade do Vale do Paraiba (IPD), Av. Shishima Hifumi 2911,12244-000 S. J. Campos, SP, Brazil
2Instituto Nacional de Pesquisas Espaciais, Av. dos Astronautas 1758, 12227-010 S. J. Campos, SP, Brazil
3STELAB, Nagoya University, 3-13 Honohara, Toyokawa 442-8507, Japan
4Physics Department, University of Tucuman, Av. Independencia 1800, 4000 San Miguel de Tucuman, Argentina
Abstract. All-sky imaging observations of the F-region OI 630nm nightglow emission allow us to
visualize large-scale equatorial plasma depletions, generally known as trans-equatorial plasma
bubbles. Strong range type spread-F is the radio signature of these (magnetically) north-south
aligned plasma depletions. An extensive database of the OI 630nm emission all-sky imaging
observations has been obtained at Cachoeira Paulista (22.7°S, 45.0°W; dip latitude ∼16°S),
Brazil, between the years 1987 and 2000. An analysis of these observations revealed that
relatively few large-scale ionospheric plasma depletions occur during the months of May to
August (southern winter, June solstice) in the Brazilian sector. Of the few that are observed
during these months, some occur in association with geomagnetic storms and some do not. In
this paper, a detailed analysis of the events when large-scale ionospheric plasma depletions were
initiated and evolved during the June solstice periods are presented and discussed.
Key words.
Atmospheric composition and chemistry (airglow and aurora).
Ionosphere (equatorial ionosphere; ionospheric irregularities)
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