engleski

Investigation of geomagnetic and solar activity over time span 1960-2001

The solar-terrestrial relationship has been widely studied by means of space weather indices and various solar wind parameters. In this study we perform such an investigation over four decades (1960--2001) on the global scale, and for the first time on the regional scale as well. The variations regarded as the remaining external field signal (thereafter RES) and present in the European observatory annual means of the Northward, X, magnetic component is used as an indicator of the regional geomagnetic activity and are investigated regarding different processes occurring on the Sun. In order to understand how various geomagnetic activity indices respond to the interplanetary disturbances during different periods of the solar cycle, the annual means of the solar activity index, F10.7, and geomagnetic Ap and Dst indices, are studied. The indices are inherently complex since they include contributions from different solar phenomena. By studying the cross-correlations we aim to distinguish between different generation mechanisms. The relationships between the solar parameter F10.7 and RES, Dst, Ap, characterized by high cross-correlation coefficients, suggest the possibility to evaluate the behaviour of these geomagnetic parameters on short timescale. We found finite time lags among the investigated parameters. Our study suggests a one year delay of both RES and Dst after F10.7. The Ap is clearly delayed for about two years with respect to F10.7 and about one year with respect to Dst and RES. This indicate that the Ap responds to the solar activity in a different manner than Dst and RES, which are dominated by the coronal mass ejections activity. On the other hand, it seems that Ap is more sensitive to the high--speed streams (HSS) and Alfvenic waves present in HSS. The existence of time lags gives us the possibility to forecast different parameters. Importantly, the proposed forecasting procedure offers the possibility to reconstruct the F10.7 from the inferred geomagnetic activity for the epochs prior to solar activity monitoring. This study contributes to understanding some physical processes on the Sun that cause the perturbations in the near-Earth interplanetary space and consequently in the Earth's magnetic field. Moreover such investigations may provide a better insight into the time evolution of the open and closed solar magnetic field, and into long term changes in the solar activity with related physical processes.

solar physics; astrophysics; and astronomy

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