Magnetic storms are a central element of space weather: they have severe impacts on both space-borne and ground-based technological systems and therefore their prediction is a major goal of the space community. The most widely used statistical describer of magnetic storm activity is the Dst index. Balasis et al. (2006) applied a wavelet analysis technique to the Dst time series and showed that distinctive alterations in the scaling parameters of the index occur as an intense magnetic storm approaches. A similar spectral signature, i.e., transition from anti-persistent to persistent behavior prior to the storm, was not found for the main driver of the Dst index, the VBSouth electric field component. Therefore it was indicated that while the magnetosphere is mostly driven by the solar wind the critical feature of persistency in the magnetosphere is the result of a combination of solar wind and internal magnetospheric activity rather than interplanetary variations alone. Physical mechanisms originating in the magnetosphere and possibly related to the revealed behavior will be discussed.