Power laws in solar flares: Self-organized criticality or turbulence?

The statistics of quiescent times tau(L) between successive bursts of solar hares activity, performed using 20 years of data, displays a power law distribution with exponent alpha similar or equal to 2.4. This is an indication of an underlying complex dynamics with long correlation rimes. The observed scaling behavior is in contradiction with the self-organized criticality models of solar flares which predict Poisson-like statistics. Chaotic models, including the destabilization of the laminar phases and subsequent restabilization clue to nonlinear dynamics, are able to reproduce the power law for the quiescent times. A shell model of MWD turbulence correctly reproduces all the observed distributions.