On the Generative Process of Solar Flares: Non-Poisson Behavior
The number of solar flares occurring in the corona is strongly correlated with the phase of the solar cycle. It is common practice to describe the yearly flare count distributions with a Poisson distribution. We find that the observed distributions are overdispersed relative to that expected from Poisson, and thus conclude that a Poisson generative model is not appropriate to fit to flare data aggregated in that manner. We propose that only those flares that occur within a given active region should be modeled as a Poisson process, finding that this is only the case for about 50% of active regions from which a considerable number of flares originate. The accumulation of flares from several concurrent active regions explains the observed properties of flares counts. This result has a limiting impact on assumptions for describing the physical processes of solar flare occurrences, as well as the analysis and modeling of the distribution of flares energies, which are known to be distributed as power-laws.