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Found 6 entries in the Bibliography.
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2012 |
Equatorial ionospheric responses during two magnetic storms of moderate intensity are investigated, for the first time, by conjugate point observations in Brazil. The study focuses on storm-induced changes in the evening prereversal vertical drift, thermospheric trans-equatorial winds, spread F/plasma bubble irregularity development, electron density/plasma frequency heights, the EIA strength, and zonal plasma drifts. It is based on data obtained from five Digisondes operated in Brazil, three of them being part of a conjugate point equatorial experiment (COPEX) involving a dip equatorial and two magnetic conjugate sites at \textpm12\textdegree. The other two were operated at the equatorial ionization anomaly (EIA) trough and crest locations at nearby magnetic meridians. The results bring out, and clarify, many outstanding aspects of the strong influence of storm time electric fields on the equatorial ionosphere at different phases of the two long lasting storm sequences. During both storms prompt penetration electric fields dominated the ionospheric response features as compared to the disturbance wind dynamo effects that were not very conspicuous. An under-shielding (over-shielding) electric field occurring in the evening hours causes enhancement (suppression) of the prereversal vertical drift and post sunset spread F/plasma bubble generation. The same electric fields cause post sunset EIA enhancement and suppression, respectively. Post sunset (post midnight) spread F can develop from under-shielding (over-shielding) electric fields, while it can be disrupted by over-shielding (under-shielding) electric field. Trans-equatorial winds are found to be ineffective to stabilize the post sunset F region against the destabilizing effect of strong prereversal vertical drift. Storm time westward plasma drifts are found to be driven by prompt penetration eastward electric fields (through their effect of inducing vertical Hall electric fields), rather than by a disturbance westward thermospheric wind during these storms. Abdu, M.; Batista, I.; Bertoni, F.; Reinisch, B.; Kherani, E.; Sobral, J.; Published by: Journal of Geophysical Research Published on: 05/2012 YEAR: 2012   DOI: 10.1029/2011JA017174 Equatorial ionosphere; Magnetic storms; plasma bubbles; plasma drifts; spread F; transequatorial winds |
2009 |
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\textdegree) and from a digisonde operated at another equatorial site (dip angle: -11.5\textdegree) 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. Abdu, M.; Kherani, Alam; Batista, I.; de Paula, E.; Fritts, D.; Sobral, J.; Published by: Annales Geophysicae Published on: Jan-01-2009 YEAR: 2009   DOI: 10.5194/angeo-27-2607-2009 |
Overview and summary of the Spread F Experiment (SpreadFEx) We provide here an overview of, and a summary of results arising from, an extensive experimental campaign (the Spread F Experiment, or SpreadFEx) performed from September to November 2005, with primary measurements in Brazil. The motivation was to define the potential role of neutral atmosphere dynamics, specifically gravity wave motions propagating upward from the lower atmosphere, in seeding Rayleigh-Taylor instability (RTI) and plasma bubbles extending to higher altitudes. Campaign measurements focused on the Brazilian sector and included ground-based optical, radar, digisonde, and GPS measurements at a number of fixed and temporary sites. Related data on convection and plasma bubble structures were also collected by GOES 12, and the GUVI instrument aboard the TIMED satellite.\ Fritts, D.; Abdu, M.; Batista, B.; Batista, I.; Batista, P.; Buriti, R.; Clemesha, B.; Dautermann, T.; de Paula, E.; Fechine, B.; Fejer, B.; Gobbi, D.; Haase, J.; Kamalabadi, F.; Kherani, E.; Laughman, B.; Lima, P.; Liu, H.-L.; Medeiros, A.; Pautet, P.-D.; Riggin, D.; Rodrigues, F.; Sabbas, F.; Sobral, J.; Stamus, P.; Takahashi, H.; Taylor, M.; Vadas, S.; Vargas, F.; Wrasse, C.; Published by: Annales Geophysicae Published on: Jan-01-2009 YEAR: 2009   DOI: 10.5194/angeo-27-2141-2009 |
Takahashi, H.; Taylor, M.; Pautet, P.-D.; Medeiros, A.; Gobbi, D.; Wrasse, C.; Fechine, J.; Abdu, M.; Batista, I.; Paula, E.; Sobral, J.; Arruda, D.; Vadas, S.; Sabbas, F.; Fritts, D.; Published by: Annales Geophysicae Published on: Jan-01-2009 YEAR: 2009   DOI: 10.5194/angeo-27-1477-2009 |
The Spread F Experiment (SpreadFEx): Program overview and first results Fritts, D.; Abdu, M.; Batista, B.; Batista, I.; Batista, P.; Buriti, R.; Clemesha, B.; Dautermann, T.; de Paula, E.; Fechine, B.; Fejer, B.; Gobbi, D.; Haase, J.; Kamalabadi, F.; Kherani, E.; Laughman, B.; Lima, J.; Liu, H.-L.; Medeiros, A.; Pautet, P.-D.; Riggin, D.; Rodrigues, F.; Sabbas, Sao; Sobral, J.; Stamus, P.; Takahasi, H.; Taylor, M.; Vadas, S.; Vargas, F.; Wrasse, C.; Published by: Earth Planets Space Published on: |
2007 |
During the SpreadFEx campaign from September 22 to November 8, 2005, two airglow CCD imagers, located at near Brasilia (14.8S, 47.6W, Mag. 10S) and at Cariri (7.4S, 36.5W, Mag. 9S) were operated simultaneously and measured the equatorial ionospheric bubble structures and their time evolution by monitoring the OI 6300 emission. From the 10 nights of coincident data, we observed that on some nights the bubbles was formed at the west of Cariri, but not seen from the Brasilia site. This suggests that the bubble formation and development started near the Cariri observation site. Identification of a longitudinal zone where the SpF is seeding is very important in order to find the mechanism of formation. The present paper will discuss SpF seeding mechanisms and possible contribution of the mesospheric gravity wave activity. Takahashi*, H.; Pautet, P.-D.; Fechine, J.; Abdu, M.; Batista, I.; Paula, E.; Sobral, J.H.A.; Gobbi, D.; Arruda, D.; Batista, P.; Sabba, F.; Taylor, M.; Medeiros, A.; Buriti, R.; Wrasse, C.; Fritts, D.; Published by: Published on: YEAR: 2007   DOI: 10.1190/sbgf2007-404 |
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