The solar wind has an important impact on the Earth and its magnetic field. Among the solar wind perturbations, there can be jumps in the solar wind dynamic pressure as well as strong magnetic excursions in the z-component of the Interplanetary Magnetic Field (IMF B_(Z )). When coronal mass ejections and other solar disturbances take place in the solar wind, there can be clear changes in the global geomagnetic field, as measured by a magnetic index called Sym-H. In this thesis some unusual events were found for which there were large fluctuations either in the solar wind dynamic pressure or in the IMF B_Z but not simultaneously in both. These events suggest that the response of the geomagnetic field to the dynamic pressure fluctuations of the solar wind is variable. In particular, it was found that the earthward component (x-component) of the IMF appeared to influence the magnitude of the Sym-H response. By contrast, there was no visible impact of the y-component of the IMF. In a second exceptional event it was found that the IMF was changing substantially while the solar wind dynamic pressure remained very constant. From this study a time delay between the IMF B_Z component and the resulting Sym-H was found to be of the order of 60 to 90 minutes.

Made available in DSpace on 2015-03-03T15:15:23Z (GMT). No. of bitstreams: 1 RicardoYLCC.pdf: 1891236 bytes, checksum: 8ace5aade037fc65d63b7016813f90c7 (MD5) Previous issue date: 2008-02-29 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Satellites signals present disturbances (scintillations), due to presence of irregularities in the ionospheric plasma. In the present work, we dedicate to the study of the attenuation of these scintillations that is, an improvement in the signal, during the main magnetic storm phase during the period of October 2006 to February 2007. Using amplitude of scintillation 1.5GHz (L1) data of the net of satellites GPS, in the ionospheric station of Natal (5.84o S, 35.20o O, -20o dip) and geomagnetic indices, during the minimum solar cycle (referred to as cycle 23), demonstrating its anti-correlation between magnetic activity (Kp) and index of scintillation (<S4>) (Bonelli2005 method, that works for solar maximum, Bonelli(2005)). These results show that these storms correspond to category I of Aarons (1991). The magnetic storms can generate irregularities when the electric feld of penetration eastward on the pre-reversal hour intensificating that and can too generate irregularities on midnight and sunlight period. The limitation of the method applied here is that it is not considering some storms that had also occurred during equinox and summer in the Brazilian region. For this reason, we will use additional data of the stations of S?o Jo?o de Cariri (Imager and Photometer) and of the station at Fortaleza (Digissonde data), as aid to analyze these storms. The storms that had been left out by the applied method, fit in the other two categories of Aarons, with one only exception (storm of January, 02). We show that in the day of the main phase of the magnetic storm, and with presence of bubbles (according to data of the Imager and Photometer), the speed of vertical drift ~E ~B (hF=t) is below 20m/s, that is the threshold found for Anderson al., (2004) (>20m/s as condition favorable to the formation of irregularities and increase in the scintillation index). This reduction of the speed is due to solar minimum / Sinais de sat?lites apresentam perturba??es (cintila??es), devido ? presen?a de irregularidades no plasma ionosf?rico. No presente trabalho, dedicamo-nos ao estudo da atenua??o dessas cintila??es ou seja, uma melhoria no sinal, durante a fase principal de tempestades magn?ticas presentes no per?odo de outubro 2006 a fevereiro 2007. Usando-se dados de cintila??es na amplitude de sinais de 1.5GHz da rede de sat?lites de GPS, na esta??o ionosf?rica de Natal (5.84o S, 35.20o O, -20o dip) e ?ndices geomagn?ticos, durante o m?nimo do ciclo solar que acaba de terminar (denominado ciclo 23), demostrando-se a anticorrela??o entre atividade magn?tica (Kp) e o ?ndice de cintila??o S4, que ? uma medida das cintila??es na amplitude do sinal de um sat?lite (m?todo Bonelli2005, que foi comprovado para per?odos de m?ximo solar), isto quando a fase principal da tempestade magn?tica acontece durante horas de dia local. Encontra-se, que estas tempestades correspondem ? categoria I de Aarons (1991). As tempestades magn?ticas podem gerar irregularidades quando o campo el?trico de penetra??o ? para leste na hora do pico pr?-revers?o ao intensificando-o e tamb?m podem gerar irregularidades no per?odo entre meia noite e o amanhecer. A limita??o do m?todo aplicado ? que n?o considera algumas tempestades que tamb?m ocorreram durante este per?odo de equin?cio e ver?o na regi?o brasileira. Ent?o, utiliza-se dados adicionais das esta??es de S?o Jo?o de Cariri-PB (Imageador All Sky e Fot?metro) e da esta??o de Fortaleza-CE (dados de digisonda), para analisar estas tempestades. As tempestades que foram deixadas de fora pelo m?todo aplicado, encaixam-se nas outras duas categorias de Aarons, com uma ?nica exce??o (tempestade do 02 de Janeiro). Mostramos que no dia da fase principal, e com presen?a de bolhas (segundo os dados do Imageador e Fot?metro), a velocidade de deriva vertical E ~B ( h F= t) est?o abaixo de 20m/s, que ? o limiar encontrado por Anderson et al., v (2004) (>20m/s como condi??o favor?vel ? forma??o de irregularidades e aumento no ?ndice de cintila??o). Esta diminui??o da velocidade ? devido ao m?nimo solar