Variability of the Occurrence Frequency of Solar Flares and the Statistical Flare
Abstract
Self-Organized Criticality (SOC) embedded in cellular automata models has been so far acknowledged as an adequate qualitative way of studying the statistical behaviour of flaring activity in solar active regions. These models are able of producing robust power laws featuring the frequency distributions of the events obtained, which are closely consistent with observations of flares, as well as much steeper power-law cut-offs, which may indicate the existence of the presently unobserved nanoflares. SOC models are based on the substantial concept that active regions are driven dissipative nonlinear dynamical systems. The role of the external driver is attributed to the feedback of magnetic flux that is injected to the system through the photospheric boundary and to the random shuffling of the footpoints of coronal loops taking place on the upper photosphere. In previous numerical studies, the driver used was an infinitesimal perturbation acting on localized magnetic topologies due to which avalanche-type instabilities were triggered. Furthermore, the resulting power-law indices were unique. Recent observations, however, have shown that the scaling indices of flares' frequency distributions are not kept constant during certain phases of the solar activity, such as the 154-day periodicity. To tackle this problem we investigate the role of the driver used, by introducing a highly variable driving mechanism. We show that the variability of the driver induces a respective variability in the resulting power-law indices. The variability of the indices can be well represented by a linear dependence between them and the driver's scaling index for both "nanoflaring" and "flaring" activity. Furthermore, a first attempt of connecting the driver with certain statistical properties of active regions is introduced. The results stand closely in favor of the observations of flaring activity during the 154-day periodicity.
- Publication:
-
Joint European and National Astronomical Meeting
- Pub Date:
- 1997
- Bibcode:
- 1997jena.confE..39G