The vertical magnetic field strength (white/black being positive/negative, scaled to 500 G) of HARP 833 i.e. NOAA AR 11283 (cf. Fig. 3), showing regions identified as strong-gradient magnetic neutral lines for which the ℛ_nwra parameter is calculated (green boxes) with the 0.68-level contour of the Gaussian-convolved bitmap indicated (purple contours). Similar masks are used for the “magnetic neutral line”-related parametrizations.