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Browsing Artículos Científicos by Author "Abreu, A. J. de"
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Item Restricted Effects of the intense geomagnetic storm of September–October 2012 on the equatorial, low- and mid-latitude F region in the American and African sector during the unusual 24th solar cycle(Elsevier, 2015-12-30) Jesus, R. de; Fagundes, P. R.; Coster, A.; Bolaji, O. S.; Sobral, J. H. A.; Batista, I. S.; Abreu, A. J. de; Venkatesh, K.; Gende, M.; Abalde, J. R.; Sumod, S. G.The main purpose of this paper is to investigate the response of the ionospheric F layer in the American and African sectors during the intense geomagnetic storm which occurred on 30 September–01 October 2012. In this work, we used observations from a chain of 20 GPS stations in the equatorial, low- and mid-latitude regions in the American and African sectors. Also, in this study ionospheric sounding data obtained during 29th September to 2nd October, 2012 at Jicamarca (JIC), Peru, São Luis (SL), Fortaleza (FZ), Brazil, and Port Stanley (PST), are presented. On the night of 30 September–01 October, in the main and recovery phase, the h´F variations showed an unusual uplifting of the F region at equatorial (JIC, SL and FZ) and mid- (PST) latitude stations related with the propagations of traveling ionospheric disturbances (TIDs) generated by Joule heating at auroral regions. On 30 September, the VTEC variations and foF2 observations at mid-latitude stations (American sector) showed a long-duration positive ionospheric storm (over 6 h of enhancement) associated with large-scale wind circulations and equatorward neutral winds. Also, on 01 October, a long-duration positive ionospheric storm was observed at equatorial, low- and mid- latitude stations in the African sector, related with the large-scale wind circulations and equatorward neutral winds. On 01 and 02 October, positive ionospheric storms were observed at equatorial, low- and mid-latitude stations in the American sector, possibly associated with the TIDs and an equatorward neutral wind. Also, on 01 October negative ionospheric storms were observed at equatorial, low- and mid-latitude regions in the American sector, probably associated with the changes in the O/N2 ratio. On the night of 30 September–01 October, ionospheric plasma bubbles were observed at equatorial, low- and mid- latitude stations in the South American sector, possibly associated with the occurrence of geomagnetic storm.Item Restricted Numerical modeling of ionospheric effects in the middle‐ and low‐latitude F region during geomagnetic storm sequence of 9-14 September 2005(American Geophysical Union, 2011-05-27) Klimenko, M. V.; Klimenko, V. V.; Ratovsky, K. G.; Goncharenko, L. P.; Sahai, Y.; Fagundes, P. R.; Jesus, R. de; Abreu, A. J. de; Vesnin, A. M.This study presents the Global Self‐Consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) numerical simulations of the 9–14 September 2005 geomagnetic storm effects in the middle‐ and low‐latitude ionosphere. Recent modifications to the GSM TIP model include adding an empirical model of high‐energy electron precipitation and introducing a high‐resolution (1 min) calculation of region 2 field‐aligned currents and a cross‐cap potential difference. These modifications resulted in better representation of such effects as penetration of the magnetospheric convection electric field to lower latitudes and the overshielding. The model also includes simulation of solar flare effects. Comparison of model results with observational data at Millstone Hill (42.6°N, 71.5°W, USA), Arecibo (18.3°N, 66.8°W, Puerto Rico), Jicamarca (11.9°S, 76.9°W, Peru), Palmas (10.2°S, 48.2°W, Brazil), and San Jose Campos (23.2°S, 45.9°W, Brazil) shows good agreement of ionospheric disturbances caused by this storm sequence. In this paper we consider in detail the formation mechanism of the additional layers in an equatorial ionosphere during geomagnetic storms. During geomagnetic storms, the nonuniform in height zonal electric field is generated at the geomagnetic equator. This electric field forms the additional layers in the F region of equatorial ionosphere.