An Information Theory Approach to Storm-Substorm Relationship

The storm-substorm relationship is one of the most intriguing and debated aspects of the global magnetospheric response to solar wind changes. Although since the early 90s several studies on the O+ ions of ionospheric origin ions evidenced the relationship between magnetospheric substorms and large magnetic storms, this link is still under investigation. Here, we present the first results on the existence of a clear transfer of information among these two classes of magnetospheric phenomena by approching this problem via the information theory. In detail, the investigation of transfer entropy [Schreiber, Phys. Rev. Lett., 85, 465, 2000] between two proxies of these phenomena (AL-index and Dst-index) clearly suggests the existence of a statistical evidence for the driving of geomagnetic storms from substorms. The characteristic time delay in transfer of information is found to be below 1hr.