Effect of Solar Wind Fluctuations on Geomagnetic Activity

Abstract

The term space weather refers to conditions on the Sun and in the solar wind, the magnetosphere, ionosphere and thermosphere that can influence the performance and reliability of space-borne and ground-based technological systems and pose danger on human life or health. The time scales of interest in space weather processes are determined by the intrinsic nature of the processes themselves and the lead time that the predictions can be given. In order to predict an event, some indications of it must be observed in advance. Due to the distance between the Sun and the Earth, the solar wind and energetic particles' speed etc, our capability in predicting the solar wind properties impacting the Earth is poor. We are currently limited to at best warnings 80 hours in advance and predictions at maximum 1 hour before the event starts.

This thesis studies the relationship between the solar wind ULF power fluctuations and the magnetospheric activity using the known solar wind - magnetosphere coupling functions and the activity indices. The magnetospheric activity index AL has been presented as a function of different solar wind driving parameters and their level of fluctuations to deduce the significance of the fluctuations in generating magnetospheric activity. In order to examine the effects of specific fluctuation frequencies, the power at different frequencies was integrated using wavelet analysis with the Morlet mother wavelet.

Our results show some points about the solar wind-magneotsphere coupling: 1)They approve the difference between the northward and southward IMF in driving the magnetospheric activity; 2)They demonstrate that the ULF IMF fluctuations can noticeably increase the activity level such that the higher the fluctuation power, the stronger the activity level; 3)The results provide further evidence to the previous findings indicating that under certain circumstances, northward IMF can also trigger activity; 4)Our results indicate that fluctuations in the solar wind speed can also have a small enhancing effect on the AL index; however, this effect is not isolated to the ULF range.