Arrows depict Lorentz (top left: blue) and pressure forces (top right: red) in the z = 0 plane. Bottom left: the combination of Lorentz and pressure forces (green). The solid black lines show a selection of field lines and the “+” sign indicates the null point position. Bottom right: field lines traced from around the null in 3D. Taken at t = 2.0 for the case of one pulse with v₀ = 0.04, τ = 1.8, A_d = 80 and η = 5 × 10^-4. (This figure is available in color in the electronic form.)