Short Term Memory and Clustering of Solar Flares

The solar magnetic activity cycle provides energy input that is released in intense bursts of radiation known as solar flares. As such, the dynamics of the activity cycle is embedded in the sequence of times between the flare events. Recent analyses [Snelling et al., 2020, Ashwanden and Johnson, 2021] show that solar flares exhibit memory on different timescales. Information theory analysis shows that the time ordering of flare events is not random, but rather that there is dependence between successive flares. The increased mutual information results from the clustering of flares, which we demonstrate by comparing the cumulative distribution function of successive flares with the cumulative distribution function of surrogate sequences of flares obtained by random permutation of flares within rate-variable Bayesian blocks during which it is assumed that the flare rate is constant. Differences between the cumulative distribution functions are substantial on a timescale of around 3 hours, suggesting that flare recurrence on that timescale is more likely than would be expected if the waiting time were drawn from a nonstationary Poisson process.