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 dis tribution with exponent alpha similar or equal to 2.4. This is an indicatio n of an underlying complex dynamics with long correlation rimes. The observ ed scaling behavior is in contradiction with the self-organized criticality models of solar flares which predict Poisson-like statistics. Chaotic mode ls, including the destabilization of the laminar phases and subsequent rest abilization clue to nonlinear dynamics, are able to reproduce the power law for the quiescent times. A shell model of MWD turbulence correctly reprodu ces all the observed distributions.