Waiting time statistics in solar flares

Solar flares activity is investigated by looking at the statistics of the waiting times between hard X-ray bursts. It is found that the distribution has a power-law tail which indicates the existence of nontrivial dynamics with long-range correlations. A shell model for MHD turbulence is capable to reproduce the power-law distribution through an identification of the intermittent bursts of dissipation with solar flares. This result suggests that the nonlinear dynamics could play a role more relevant than the particular topology associated with the field configuration. Comparisons with results from models based on self-organized criticality are made.