WLFs in NOAA AR 11515. Panel a: 70 flares (C- and M-classes) occurred between E45° and W45°. The solid line is GOES soft X-ray (1–8 Å). The red dashed lines mark the peak times of WLFs, and the black dotted lines mark the peak times of normal flares. Panels b–e: locations of these WLFs in the active region. The circles in panels b and c show WLFs 1–12, while the circles in panels d and e show WLFs 13–20. Panels b and d: HMI continuum images at two different times, panels c and e: HMI line-of-sight magnetograms at two different times. The black boxes R1, R2, and R3 in panels b and d mark the quiet-Sun regions we selected to estimate the error in the measured continuum intensity. The size of each box is 20 × 20 pixels.