Estudo estatístico da variabilidade dos índices geomagnéticos e sua relação com o ciclo solar / Statistical study of the variability of geomagnetic indices and its relation to the solar cicle

AUTOR(ES)
DATA DE PUBLICAÇÃO

2002

RESUMO

A study of the long-term relation between solar and geomagnetic activity is presented. For that purpose we have used of the annual and monthly sunspot number series (Rz) together with the aa geomagnetic index from 1868 to 2000. Furthermore, we have analized the Dst, AE and Ap indices (from 1957 to 2000), and solar wind speed. In this study, statistical analysis techniques and harmonic analysis were used. The most significant periods obtained with the spectral analysis in the aa and Rz time series were those of 11 years in both series, and 4.3 years and 6 months in the aa series. In the long-term analysis of the Rz and aa series it was observed a tendency of increasing of the 11 and 22 years running average, with time, being more intense in the aa series. The cross correlation analysis between Rz and aa, through the cycles, showed that the correlation coefficient diminishes while the lag between both series increase. A multiple regression was also made to obtain the aa index from the Rz series combined with the high-speed solar wind streams (Fpk500), which revealed that approximately 71% of the aa variability can be explained by the variabilities in the Rz and Fpk500 time series. It was observed in the present work that the cross correlation between aa index and Fpk500 is better than the cross correlation between aa index and Rz. The geomagnetic activity represented by the aa index is sensitive to the high-speed stream solar wind related structures. It was also performed a inter correlation between various indices, AE, Dst, Ap and aa for long periods, as well as their relation with Rz and Fpk500. The results of this inter correlation showed that the Dst and the AE indices are well correlated with the aa and Ap indexes. It was found that 75% of the aa variability can be obtained through a linear relation between the Dst and the AE indeces. The Ap index has a similar behavior, 73% of its variability is described through a linear combination of these same both indices.

ASSUNTO(S)

variability índice estatística solar cycles variabilidade geomagnetismo geomagnetism statistics indexes ciclo solar

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