Fitting parameters of the nanoflare frequency distributions as a function of time and correlated to the ISN. Top: power-law index α (left) and frequency at 10²⁵ erg (right) as a function of time along with the 13-month smoothed monthly mean ISN. The fitting error for both parameters is shown as red vertical lines. Bottom: scatter plots of both fitting parameters against ISN. A linear function (blue) was fitted to the data, yielding the indicated Pearson correlation coefficient r together with the uncertainty range.