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Articles by J.R. de Souza
Total Records ( 2 ) for J.R. de Souza
  L.A. McKinnell , M.W. Paradza , P.J. Cilliers , M.A. Abdu and J.R. de Souza
  The probability of occurrence of spread-F can be modeled and predicted using neural networks (NNs). This paper presents a feasibility study into the development of a NN based model for the prediction of the probability of occurrence of spread-F over selected equatorial stations within the Brazilian sector. The input space included the day number (seasonal variation), hour (diurnal variation), sunspot number (measure of the solar activity), magnetic index (measure of the magnetic activity) and magnetic position. Twelve years of spread-F data from Brazil (covering the period 1978–1989) measured at the equatorial site Fortaleza (3.9°S, 38.45°W ) and low latitude site Cachoeira Paulista (22.6°S, 45.0°W ) are used in the development of an input space and NN architecture for the model. Spread-F data that is believed to be related to plasma bubble developments (range spread-F) was used in the development of the model. The model results show the probability of spread-F occurrence as a function of local time, season and latitude. Results from the Brazilian Sector NN (BSNN) based model are presented in this paper, as well as a comparative analysis with a Brazilian model developed for the same purpose.
  M.A. Abdu , I.S. Batista , C.G.M. Brum , J.W. MacDougall , A.M. Santos , J.R. de Souza and J.H.A. Sobral
  We present the results of a study of the equatorial evening F region prereversal vertical drift enhancement over Brazil as a function of solar flux (F10.7). The vertical drift is measured from true heights obtained from digisondes operated at an equatorial site, Sao Luis, and at an off equatorial site, Fortaleza. The different magnetic inclinations of the two sites cause different degree of dependence of the vertical drift on magnetic meridional winds permitting an evaluation of the solar flux control on both the evening vertical drift (zonal electric field) and meridional winds. The analysis period covers the year 2001 and 2004 during which the monthly mean F10.7 varied from 245 to 80. The solar flux dependence of the vertical drift of the evening F layer as obtained from the data are compared with the representation of such dependence in the IRI model. While the IRI description of such dependence appears comparable to that is determined from observational data there is significant difference between the drift values in the two cases, the IRI representation being an under-estimation of the observed drift for all flux values. The results are discussed from the perspective of validating the IRI model representations of the vertical drift. The results of the study also shows that the HWM description of the evening thermospheric meridional wind in the Brazilian sector, shows agreement with observation for lower F10.7 values, while it significantly deviates from the observed/calculated meridional wind for higher solar flux values.
 
 
 
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