ANGEO Annales Geophysicae ANGEO 1432-0576 Copernicus GmbH Göttingen, Germany 10.5194/angeo-22-3211-2004 Response of the equatorial and low-latitude ionosphere during the space weather events of April 2002 Lima W. L. C. 1 Becker-Guedes F. 2 Sahai Y. 2 Fagundes P. R. 2 Abalde J. R. 2 Crowley G. 3 Bittencourt J. A. 4 Centro Univ. Luterano de Palmas (CEULP), Universidade Luterana do Brasil (ULBRA), 77054-970 Palmas, TO, Brazil Universidade do Vale do Paraíba (UNIVAP), 12244-000 São José dos Campos, SP, Brazil Southwest Research Institute, San Antonio, TX 78238-5166, USA Instituto Nacional de Pesquisas Espaciais (INPE), 12201-970 São José dos Campos, SP, Brazil 23 09 2004 22 9 3211 3219 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.ann-geophys.net/22/3211/2004/angeo-22-3211-2004.html The full text article is available as a PDF file from http://www.ann-geophys.net/22/3211/2004/angeo-22-3211-2004.pdf

A digital ionosonde, of the type known as Canadian Advanced Digital Ionosonde (CADI), has been in routine operation at S&#227;o Jos&#233; dos Campos (23.2&deg; S, 45.9&deg; W; dip latitude 17.6&deg; S), Brazil, since August 2000. A new CADI was installed at Palmas (10.2&deg; S, 48.2&deg; W; dip latitude 5.5&deg; S), Brazil, in April 2002. The two CADIs are part of a new network being established in a collaborative program between UNIVAP and CEULP/ULBRA, to study the equatorial and low-latitude ionospheric regions in Brazil. In this paper we present and discuss the effects of the space weather events during 17-20 April 2002, as evidenced by the ionospheric parameter changes from simultaneous observations at S&#227;o Jos&#233; dos Campos and Palmas. A comparison of the observed ionospheric parameters (<i>h'F</i>, <i>hpF2</i> and <i>foF2</i>) at the two stations, separated only by about 1460km, shows both similarities and differences associated with the geomagnetic disturbances. Also, a comparison of the observed <i>F</i>-region parameters with the ASPEN-TIMEGCM model results is presented. The model results show reasonable agreement during the quiet period of observations, but some discrepancies have been observed during the geomagnetic disturbances.