Initial state of the model AR variables, showing a cut in the x–z plane at y = 0 for the 3D dipole magnetic field with d = 2.5. (a) Initial density, ρ, and selected magnetic field lines. (b) Initial fast magnetosonic speed, V_f. The color map and contours show the spatial dependence of V_f. (c) Initial normalized background temperature, T. (d) Initial values of plasma β.