a) indicates the number of nulls present in the Hall MHD simulations. The remaining figures illustrate the evolution of current at each null; the values of b) J_z and c)  | J |  −  | J_z |  at an individual null are shown, comparing the single null case (λ_i = 0.0072, in red) with values at every null in the λ_i = 0.072 simulations. When multiple nulls are present, each null is uniquely identified by a combination of colour and symbol, identical to that outlined in Fig. 5 (e.g. 7 nulls, ordered according to location along the B_y = 0 line, would be identified by  ×  +  △    (in   blue)    ∗    (in   black)   □ +  ×    (in   green)).