Panel a: relationship between WL enhancement (, the average enhancement of WL emission in the WLF region) and AIA 1600 Å intensity (, the ratio between the average AIA 1600 Å intensity in the WLF region and the maximum 1600 Å intensity in the whole flare region) for 20 WLFs in NOAA AR 11515. The positive correlation indicates that a WLF has a stronger WL emission if it occurs closer to the center of the whole flaring region. Panel b: relationship between WL enhancement () and magnetic field change (|dB_l|, the absolute change of the unsigned B_l in WLF region). A greater enhancement of the WL emission is often accompanied by a greater change in the line-of-sight magnetic field.