Nonstationary Fast-driven, Self-organized Criticality in Solar Flares

The original concept of self-organized criticality, applied to solar flare statistics, assumed a slow-driven and stationary flaring rate, which implies timescale separation (between flare durations and interflare waiting times). The concept reproduces power-law distributions for flare peak fluxes and durations, but predicts an exponential waiting time distribution. In contrast to these classical assumptions, we observe (i) multiple energy dissipation episodes during most flares, (ii) violation of the principle of timescale separation, (iii) a fast-driven and nonstationary flaring rate, (iv) a power-law distribution for waiting times Delta t, with a slope of alpha(Delta t) approximate to 2.0, as predicted from the universal reciprocality between mean flaring rates and mean waiting times, and (v) pulses with rise times and decay times of the dissipated magnetic free energy on timescales of 12 +/- 6 minutes, and up to 13 times in long-duration (less than or similar to 4 hr) flares. These results are inconsistent with coronal long-term energy storage, but require photospheric-chromospheric current injections into the corona.