Self-excitation in the solar flare waiting time distribution

Abstract

Solar flares release high amounts of energy into the solar system and can negatively impact earth based systems through their effects on satellites and power systems. It is hence important to understand and forecast their occurrence. The solar flare waiting time distribution (WTD) defines the amount of time which elapses between the occurrence of successive flares and hence provides a starting point for forecasts and risk assessment. Previous research has hypothesized that the observed WTD can be derived from a simple model which posits that flares follow a nonstationary Poisson process. This Poissonian assumption has implications for fundamental physical theories about the origin of flares, since it is a direct consequence of the widely studied avalanche model. However in this paper we call the Poissonian assumption into question, by showing that the occurrence of solar flares seems to have a substantial amount of burstiness and self-excitation that continues to exist even when controlling for the solar cycle. This leads to a strong non-Poissonian dependence between the occurrence time of successive flares.