Nonlinear Processes in Geophysics www.nonlin-processes-geophys.net 1023-5809 1607-7946 9 5/6 2002 10.5194/npg-9-419-2002 http://www.nonlin-processes-geophys.net/9/419/2002/ http://www.nonlin-processes-geophys.net/9/419/2002/npg-9-419-2002.html http://www.nonlin-processes-geophys.net/9/419/2002/npg-9-419-2002.pdf 419 423 0000-00-00 Fractal time statistics of AE-index burst waiting times: evidence of metastability G. Consolini P. De Michelis Istituto di Fisica dello Spazio Interplanetario – CNR, Roma, Italy Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy Recent observations and analyses evidenced that the magnetotail, as well as the magnetospheric dynamics are characterised by a scale-free behaviour and intermittence. These results, along with numerical simulations on cellular automata, suggest that the observed scale-invariance may be due to <i>forced and/or self-organised criticality </i>(FSOC), meaning that the magnetotail operates near a marginally stable state (Chang, 1999). On the other hand, it was underlined that a complex magnetic field topology in the geotail regions may play a relevant role in the impulsive energy relaxation (Consolini and Chang, 2001.