Ionospherica F-layer nocturnal zonal drift studies over Brazilian region / Estudos das derivas zonais da camada F da ionosfera noturna sobre a região brasileira

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

This study focused on the nocturnal zonal plasma drifts of the ionosphere (F layer) at equatorial and low latitude regions of the Brazil. The analysis is interpreted using the simple plasma drift model (coupled ionosphere-electric field model of Eccles, 1998) and monochromatic digital images of the OI630nm emission, which allow direct visualization of the ionospheric bubbles. The digital images were obtained by two optical imager systems operating at São João do Cariri (equatorial geographic latitudes: 7.4°S; 36.5°W; 19oS dip latitude) and Cachoeira Paulista (low geographic latitudes: 22.5°S; 45°W; 31oS dip latitude) from October 1998 to December 2003 (peak of maximum solar activity: 2001, F10.7cm=181.4). In the total, 498 nights were observed of which 192 nights occurred ionospheric bubbles being 145 nights in geomagnetically quiet nights (&#931;KP<24+). The ionospheric bubble zonal drifts were calculated and grouped seasonally. Then, the geophysical conditions of each quiet night were considered in the equations of the model of Eccles (1998) in order to obtain the theoretical ionospheric plasma drifts between 18LT and 6LT (30 minutes intervals). The theoretical results were also grouped seasonally. The zonal ionospheric plasma drifts result from low-latitude electrodynamics with a mix of influences from E and F region conductivities and neutral wind shears in altitude and latitude. Analysis of the zonal drifts of the ionospheric bubbles suggests that postsunset zonal drifts are strongly influenced by the F layer dynamo. The statistical results showed that during the maximum solar cycle the ionospheric bubbles occur with high frequency between September and April. The low frequency between May and August was mainly associated with magnetic storms. The maximum frequencies, at Cachoeira Paulista (100%) and at São João do Cariri (96%), occurred in the Spring at 22LT-23LT. One important result is that, in quiet nights, the ionospheric bubbles (fully developed) and the ionospheric plasma derive eastward with zonal neutral winds. The maximum zonal drift velocities were observed between 20LT and 22LT. After 0LT, the zonal drift velocities decrease more rapidly at Cachoeira Paulista than at São João do Cariri. Another characteristic observed is a significant latitudinal variation in the ionospheric bubble zonal drift velocities in the equatorial and low latitude regions, which may be related to the latitudinal gradients of the zonal neutral winds.

ASSUNTO(S)

earth ionosphere derivas ionosféricas plasma bubbles ionospheric drift bolhas de plasma space geophysics região f geofÍsica espacial f region ionosfera terrestre imagens óticas optical images

ACESSO AO ARTIGO

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