From pre-storm activity to magnetic storms: a transition described in terms of fractal dynamics

Abstract

Abstract. We show that distinct changes in scaling parameters of the D st index time series occur as an intense magnetic storm approaches, revealing a gradual reduction in complexity. The remarkable acceleration of energy release -manifested in the increase in susceptibility -couples to the transition from anti-persistent (negative feedback) to persistent (positive feedback) behavior and indicates that the occurence of an intense magnetic storm is imminent. The main driver of the D st index, the V B South electric field component, does not reveal a similar transition to persistency prior to the storm. This indicates 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 solar wind variations alone. Our results suggest that the development of an intense magnetic storm can be studied in terms of "intermittent criticality" that is of a more general character than the classical self-organized criticality phenomena, implying the predictability of the magnetosphere.

Intermittency and multifractional Brownian character of geomagnetic time series

“…It is known that the Earth's magnetospheric dynamics is characterized by persistent dynamic correlations (e.g., Dobias and Wanliss, 2009) and near-criticality dynamics (e.g., Consolini, 2002;Wanliss and Uritsky, 2010), which are correlated features in self-organized critical systems in stationary conditions also away from the critical point (Woodard et al, 2007). Furthermore, the persistent character of the magnetospheric dynamics has been shown to undergo dynamical changes during magnetic storms and substorms (e.g., Wanliss, 2005;Balasis et al, 2006;Wanliss and Dobias, 2007). These points suggest that the more complex observed relation between the multifractional nature and the intermittent character of the geomagnetic fluctuations (see, e.g., Figs.…”

“…In particular, it has been noticed that the self-similarity properties of these time series change when an intense magnetospheric/geomagnetic activity event approaches. For instance, Balasis et al (2006) have shown the occurrence of an interesting transition from the anti-persistent to the persistent character in the fluctuations of Dst index, which closely corresponds to a transition from a regime of quiet to one of high magnetospheric activity, characterized by the occurrence of intense geomagnetic storms. A similar behavior has been also documented in the case of the auroral electrojet (AE) index (e.g., Uritsky and Pudovkin,and discussed in a more general scenario, involving a near forced and/or self-organized criticality (FSOC) dynamics (Consolini, 1997;Uritsky and Pudovkin, 1998;Chang, 1999;Chang et al, 2003;Consolini and Chang, 2001;Consolini and De Michelis, 2002;Wanliss and Weygand, 2007;Wanliss and Uritsky, 2010).…”

“…It has been found that the fractal character of several geomagnetic time series, for example those relative to the geomagnetic indices AE, Dst and SYM-H, changes during magnetic storms and substorms (Uritsky and Pudovkin, 1998;Wanliss, 2005;Balasis et al, 2006;Wanliss and Dobias, 2007;Dobias and Wanliss, 2009). In particular, it has been noticed that the self-similarity properties of these time series change when an intense magnetospheric/geomagnetic activity event approaches.…”

Wavelet-based multiscale analysis of geomagnetic disturbance

“…This behaviour indicates that the external geomagnetic field is a multiscale process (Uritsky et al, 2001;Balasis et al, 2006). Considering current efforts in understanding the magnetic geo-environment and improving space weather forecasting, it is evident that the use of classical methods, such as the Fourier Transform for analysing the magnetic signal, or the geomagnetic index Dst, cannot yield any information on the temporal evolution of geomagnetic storm activity .…”

“…Some previous works have demonstrated the statistical self-affinity properties observed in the geomagnetic times series (Chang, 1999;Sitnov et al, 2001;Uritsky et al, 2001Uritsky et al, , 2006Kovacs et al, 2001;Lui, 2002;Wanliss, 2005a;Balasis et al, 2006;Wanliss and Dobias, 2007).…”