2020MNRAS.491.4435H

In a limited sample of isolated solar active regions, we find that the waiting times between flares may correlate well with flare magnitudes as determined by the Geostationary Operational Environmental Satellites (GOES) soft X-ray fluxes. A 'build-up and release' (BUR) scenario for magnetic energy storage in the solar corona suggests the existence of such a relationship, relating the slowly varying subphotospheric energy sources to the sudden coronal energy releases of flares and coronal mass ejections (CMEs). Substantial amounts of research effort had not previously found any obvious observational evidence for such a BUR process. This has posed a puzzle since coronal magnetic energy storage represents the consensus view of the basic flare mechanism. We have revisited the GOES soft X-ray flare statistics for any evidence of correlations, using two isolated active regions, and have found significant evidence for a 'saturation' correlation. Rather than a 'reset' form of this relaxation, in which the time before a flare correlates with its magnitude, the 'saturation' relationship results in the time after the flare showing the correlation. The observed correlation competes with the 'obscuration' effect of reduced GOES sensitivity following a strong event, by which weaker events can be under-reported systematically. This complicates the observed correlation, and we discuss several approaches to remedy this.