(a) Azimuthal velocity field shown on both spherical surfaces and meridional cross-sections at ϕ=0 and 3 π/2 at time t=0.53 t_η. The flow takes the form of a strong prograde equatorial surface jet, with retrograde motion near the poles and in the interior. (b) Spatial structure of the magnetic field, with b_r shown on the outer boundary, and ∣b∣ in the interior. The radial field at the surface is strongly dipolar, and the interior field shows very localised activity. The surface field is much weaker than in the interior.