On the Complex Nature of Magnetic Field Fluctuations During Geomagnetic Tail Current Disruption

One of the phenomena occurring at the onset of magnetospheric substorms is the disruption of the cross-tail current. In the course of the years, this phenomenon has been clearly shown to be characterized by a large spectrum of fluctuations occurring over a large scale interval. Here, the multiscale nature and the complex features of the cross-coupling between the different scales is investigated in the case of an already studied magnetotail current disruption event, observed by a THEMIS satellite on 29 January 2008, by means of the Hilbert-Huang Transform (HHT) and an information theory approach. A particular attention is devoted to the presence of a dual cascading process: an inverse cascading process in the MHD domain (already suggested in several works) and a direct cascading process toward non-MHD scales.