Temporal evolution of the area covered by active region NOAA 10930 over the 16-h period from 02:30–18:30 UT. The area enclosed by umbral cores and pores is displayed with a dashed line. The dash-dot-dotted line refers to the penumbra, whereas the solid line denotes the total area. The times t₀, t₁, t₂, and t₃ delimit time intervals over which the linear photometric decay rates were computed (see Table 2). The gray bars depict the duration of flares (Table 1), where the thin black line marks the peak time for flares.