Contours of ξ _⊥  (top and middle) and v_z (bottom) seen through snapshots in time, for λ_i = 0.0072 (top), and λ_i = 0.072 (middle and bottom). Each case is overplotted with selected flux surfaces (contours of A_z – in white), the lines of B_x = 0 (dark green) and B_y = 0 (light green), and also the location of the null-point (indicated by a white star). (NB. while the first two columns display (x,y) ∈  [  − 6,6] , the final column zooms in to illustrate a range of only (x,y) ∈  [  − 2,2]  of the entire simulated range, (x,y) ∈  [  − 20,20] ).