Thinning of a vertical current layer as derived from the NLFFF extrapolations. (a) 3D iso-surface (in green) of jΔ/B = 0.2 (i.e., a thin current layer on top of the flare PIL). The black lines show sampled magnetic field lines of the MFR; most of these field lines cross through the current layer. (b) 3D view of the current layer. (c) Vertical slice cutting perpendicularly through the current layer at the largest value of jΔ/B. The arrows show magnetic field vectors on the slice. (d)–(f) Time evolution of the jΔ/B in a vertical cross section as denoted by the red line in (a). The arrows in the different panels give the same location of the current layer.